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Investigation of the mechanism of failure of neat cement and mortar specimens Urruela, Juan Francisco 1954

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INVESTIGATION. OF THE MECHANISM OF FAILURE OF NEAT CEMENT AND MORTAR SPECIMENS; by JUAN FRANCISCO URRHSLA A THESIS. SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n the Department of CIVIL ENGINEERING We accept this thesis as conforming to the standard required from candidates for the degree of MASTER OF APPLIED SCIENCE. Members of the Department of C i v i l Engineering. THE UNIVERSITY OF BRITISH COLUMBIA February, 1954-ABSTRACT The problem of the investigation of the mechanism of failure i n compression of neat cement and mortar specimens i s considered i n this thesis. The study was made on two hundred specimens of cement paste and mortar, of which approximately one half were tension briquets and the other half compression cylinders. The underlying theory which led to this study was that failure i n compression i n specimens with aggregate (mortar and concrete) i s due to the wedging action of the particles of aggregate within the matrix of cement paste. Steam-curing was used to avoid delay i n the hardening of cement. I t was found that the cement used was of the type which continues hardening after being steam-cured. The importance of having the specimens at a constant tempe-rature throughout their mass and at room temperature when the tests were performed was realized. An investigation of the effect of end conditions on test cylinders i n compression was conducted. I t i s considered that the confined rubber end conditions used were an improvement on testing with lubricated ends only. Observations were made on the effect of the bursting action of water i n compression tests of moist specimens. A study of the effect of stress concentration around voids was made on tension specimens. Compression specimens made of neat cement, mortar and cement with inclusions i n the form of balls were studied. Inclusions were placed i n cement cylinders to imitate the action of the aggregate i n mortar and concrete specimens. Tests on compression specimens with inclusions were useful i n the interpretation of results of tests on neat cement and mortar cylinders and in the study of the stress-strain curves. Transverse bending tests of cylinders were made with the purpose of investigating the presence of transverse cracks formed in the cylinders as a consequence of the application of compressive loads. They did not provide a good method of investigation but were very useful i n that they were an aid to realizing the effect of the horizontal cracks i n the stress-strain curves. 1 TABLE OF CONTENTS INTRODUCTION. i Brief Description of the Wedging Action Theory i i PART L  MAKING OF SPECIMENS A) COMPOSITION AND PREPARATION OF THE CEMENT PASTE AND MORTAR USED 1 a) Reasons for Proportions 1 b) Brief Description of the Components 1 c) Mixing 2 B) TYPES OF SPECIMENS USED 3 a) Identification and Marking of the Specimens 3 b) Tension Specimens 3 c) Compression Specimens 4 d) Forms 5 C) DESCRIPTION OF THE DIFFERENT KINDS OF INCLUSIONS AND THE PROCEDURES FOLLOWED TO CLEAN THEM BEFORE USE 6 a) General 6 b) Description of the different inclusions used 7 c) Cleansing of the Inclusions 7 D) MAKING OF TENSION SPECIMENS 9 a) Tension specimens without inclusions 9 b) Tension Specimens with Inclusions 9 E) MAKING OF COMPRESSION SPECIMENS 10 a) Making Cylinders without Inclusions 10 b) Capping 11 c) Making of Cylinders with Inclusions 12 F) REMOVING THE SPECIMENS FROM THE FORMS 15 a) Tension Specimens 15 b) . Compression Specimens 16 2 G) CURING THE SPECIMENS 16 a) Curing in the Moist Closet 17 b) Steam-Curing 17 H) METHOD OF DRYING THE SPECIMENS WITHOUT CRACKING. WAXING . . . 18 a) Reasons for Waxing 19 b) Type of Wax Used 19 c) Application of the Wax 19 d) How the Briquets were Waxed 19 e) How the Cylinders Were Waxed 20 I) DRYING THE SPECIMENS 20 a) Process of Drying 20 b) Precautions Before Testing Dry Specimens 22 PART II  TESTING A) TENSION TESTS 23 B) COMPRESSION TESTS 2A a) Description of the Apparatus Used 24 b) End Conditions in Compression Tests 25 c) Types of Failures Presented by Cylinders whose End Conditions at Testing were Rubber Pads Confined in Steel Caps 28 C) TESTS OF CYLINDERS IN BENDING 29 D) REPEATED LOADING IN COMPRESSION TESTS 30 E) GENERAL DESCRIPTION OF THE STRESS-STRAIN CURVES OBTAINED IN COMPRESSION TESTS 31 a) Shape 31 b) Modulus of Elasticity 31 c) How to obtain the Modulus of Elasticity from the Stress-Strain Curves 33 d) Creep 34 e) Effects of the Speed of Testing . 35 f) Shapes of the Curves of Specimens under Repeated Loading 35 g) Effects of Cracks in the Cylinders, Previous to the Tests, in the Shape of the Stress-Strain Curves 36 3; F) INVESTIGATION OF THE BURSTING ACTION OF WATER IN COMPRESSION TESTS OF MOIST SPECIMENS 3 8 PART III.  RESULTS OBTAINED A), TENSION TESTS 40 1) BRIQUETS WITHOUT INCLUSIONS 40' a) Neat Cement Briquets, Steam-Cured and Dried 4 1 b) Neat Cement Briquets, Steam-Cured and Moist 41 2) BRIQUETS WITH INCLUSIONS 4 2 I) Study of Adhesion Between Cement Paste and Glass . . 42 a) Cement Briquets with Glass Plates 4 2 b) Cement Briquets With Glass Balls 43 II) Study of Adhesion Between Cement Paste and Steel . . 44 a) Cement Briquets with Steel Plates 44 b) Cement Briquets with Steel Balls 45 III) Conclusions from Tension Tests i n Specimens with Inclusions 46 3) STUDY OF STRESS CONCENTRATION AROUND VOIDS 46 B) COMPRESSION TESTS 50. Types of Cylinders Tested 50 l ) Compression Tests on Cylinders Steam-Cured and Dry . . . 51 a) Age-Strength Relation 52 b) Relation Between the I n i t i a l Modulus of E l a s t i c i t y and the Shape of the Stress-Strain Curve 52 c) Relationship between the process of Drying the Specimens and the Shape of the Curve 53 d) Observations on the I n i t i a l Moduli of E l a s t i c i t y , Strength, Shape of Failure and Deformation of Dry Neat Cement Cylinders 54 e) Observations on Repeated Loading of Dry Neat Cement Cylinders 55 u 2) Neat Cement C y l i n d e r s Steam-Cured and M o i s t 55 a) Age-S t reng th and Age-Modulus o f E l a s t i c i t y R e l a t i o n s i n Steam-Cured M o i s t C y l i n d e r s 56 b) R e s u l t s o f T e s t s . S t r e s s - S t r a i n Curves o f Steam-Cured M o i s t C y l i n d e r s 56 I ) S i n g l e Loading Case 56 I I ) Neat Cement C y l i n d e r s , Steam-Cured and M o i s t , Tested Under Repeated Loading . . . . 58 c) S t r e n g t h , I n i t i a l Modulus o f E l a s t i c i t y , Deformat ion and Shape o f F a i l u r e o f Neat Cement C y l i n d e r s Steam-Cured and M o i s t 61 3) Neat Cement C y l i n d e r s Cured i n the M o i s t C l o s e t Only . . . 61 A) Mor ta r C y l i n d e r s , Steam-Cured and Dry 63 5) M o r t a r C y l i n d e r s , Steam-Cured and M o i s t 65 6) Cement C y l i n d e r s , Steam-Cured and D r y , w i t h G l a s s I n c l u s i o n s P l a c e d as i n P a t t e r n " I I " 67 7) Cement C y l i n d e r s , Steam-Cured and D r y , w i t h Glas s I n c l u s i o n s p l aced as i n P a t t e r n " I " 68 8) Cement C y l i n d e r s , Steam-Cured and D r y , w i t h S t e e l B a l l I n c l u s i o n s P l aced as i n P a t t e r n " I I " 72 9) Cement C y l i n d e r s , Steam-Cured and M o i s t , w i t h S t e e l B a l l I n c l u s i o n s P laced as i n P a t t e r n " I I " 73 10) Cement C y l i n d e r s , Steam-Cured and M o i s t , w i t h S t e e l B a l l I n c l u s i o n s P l aced as i n P a t t e r n " I " 76 11) Cement C y l i n d e r s , Steam-Cured and M o i s t , w i t h S t e e l I n c l u s i o n s P l a c e d as i n P a t t e r n " I I I " 77 12) Cement C y l i n d e r s , Steam-Cured and M o i s t , w i t h S t e e l I n c l u s i o n s as i n P a t t e r n " I V " 80 C) TESTS OF CYLINDERS I N BENDING. RESULTS OBTAINED 81 D) CONCLUSIONS 83 BIBLIOGRAPHY 88 TABLES Table To f o l l o w Page 1 Neat Cement B r i q u e t s , Steam-Cured and D r i e d , Waxed Around t h e i r Necks A l 2 Neat Cement B r i q u e t s , Steam-Cured and M o i s t . . . . . . . 41 3 Cement B r i q u e t s w i t h Glass P l a t e I n c l u s i o n s . . . . . . . 43 4 Cement B r i q u e t s w i t h Glass B a l l I n c l u s i o n s 44-5 Cement B r i q u e t s w i t h S t e e l P l a t e I n c l u s i o n s . 45 6 Cement B r i q u e t s w i t h S t e e l B a l l I n c l u s i o n s 45 7 Cement B r i q u e t s w i t h Cork B a l l I n c l u s i o n s 48 8 Neat Cement C y l i n d e r s , Steam-Cured and Dry 52 9 Neat Cement C y l i n d e r s , Steam-Cured and Dry . 52 10- Neat Cement C y l i n d e r s , Steam-Cured and M o i s t 56 11 Neat Cement C y l i n d e r s Cured i n the M o i s t C l o s e t Only . . . 61 12 Mor ta r C y l i n d e r s , Steam-Cured and Dry 63 13 Mor ta r C y l i n d e r s , Steam-Cured and M o i s t 65 14 Cement C y l i n d e r s Steam-Cured and Dry , w i t h G l a s s B a l l I n c l u s i o n s P l a c e d as i n P a t t e r n " I I " 67 15 Cement C y l i n d e r s Steam-Cured and Dry , w i t h Glass B a l l I n c l u s i o n s P l a c e d as i n P a t t e r n " I " 68 16 Cement C y l i n d e r s , Steam-Cured and Dry w i t h S t e e l B a l l I n c l u s i o n s P l a c e d as i n P a t t e r n " I I " 72 17 Cement C y l i n d e r s , Steam-Cured and M o i s t , w i t h S t e e l B a l l I n c l u s i o n s P l a c e d as i n P a t t e r n " I I " 73 18 Cement C y l i n d e r s Steam-Cured and M o i s t , w i t h S t e e l B a l l I n c l u s i o n s P l a c e d as i n P a t t e r n " I " 76 19 Cement C y l i n d e r s Steam-Cured and M o i s t w i t h S t e e l B a l l I n c l u s i o n s P l a c e d as i n P a t t e r n " I I I " 77 20 Cement C y l i n d e r s , Steam-Cured and M o i s t , w i t h S t e e l B a l l I n c l u s i o n s P l aced as i n P a t t e r n " I V " 80 21 C y l i n d e r Tested i n Bending 82. PHOTOGRAPHS To follow page INTRODUCTION This paper describes a series of tests on two hundred specimens of cement paste and mortar, of which approximately one half were tension briquets and the other half compression cylinders two inches i n diameter and four indies long. The object was to investigate the mechanism of failure i n compression of neat cement and mortar. The underlying theory which led to this study was that failure i n specimens with aggregate (mortar and concrete) i s due to the wedging action of the particles of aggregate within the matrix of cement paste. Compression specimens made of neat cement, of mortar, and of cement with inclusions i n the form of balls were studied. Inclusions were placed i n cement cylinders to imitate the action of the aggregate i n mortar and concrete specimens. Preliminary studies were made i n order to learn satisfactory procedures of making, curing and testing the specimens. An effective procedure of cleaning the inclusions was necessary to obtain good adhesion between the b a l l inclusions and the cement paste. The degree of adhesion attained with the different methods of cleaning was measured i n tension briquets with inclusions. Steam curing was used to avoid delay i n the hardening of cement. i i Dry and moist specimens were studied. Drying did not give satisfactory results i n specimens with inclusions, which always cracked, but the behaviour and the stress-strain curves of cracked cylinders proved useful i n the interpretation of results. An investigation of the effect of end conditions on test cylinders i n compression was conducted, and observations were made on the effect of the bursting action of water i n compression tests of moist specimens. A description of what has been done, of the results obtained and their interpretation i s presented here. In a l l probability, research along the same lines w i l l be continued i n this University. Before approaching the core of this work a brief description of the Wedging Action Theory w i l l be of assistance. BRIEF DESCRIPTION OF THE WEDGING ACTION THEORY. It was considered that compression failure i n mortar and concrete specimens could be the consequence of a bursting action due to the wedge-shaped aggregate particles, assuming the particles to be of higher modulus of e l a s t i c i t y than the cement paste. The deformation caused by the compressive load w i l l occur mostly i n the paste and very l i t t l e i n the particles, which are very r i g i d , causing mutual approach of the particles and consequently, interaction i l l stresses along their shortest lines of distance. This causes tension i n the paste between the particles,-' unless the particles are confined or held from the outside. The following i l l u s t r a t i o n w i l l help i n giving a better under-standing: Assume a small cylinder f i l l e d with sand and loaded axially. In this case the particles are held lateitlly by the walls of the cylinder, without which they can not support the load. Now, suppose the cylinder i s f i l l e d up with concrete, assuming i t to be a combination of very r i g i d particles and a much less r i g i d matrix or f i l l e r . In this case the compressive load i s partly carried by compression lengthwise through the f i l l e r , but also partly carried by the skeleton of r i g i d particles pressing on each other, which for equilib-rium would require the lateral pressure of the cylinder walls. I f the walls of the cylinder are absent the restraining effect holding the particles from spreading appart i s provided by tension i n the matrix between the particles. Failure of the specimen i s l i k e l y to be due to this l a t e r a l tension i n the matrix, rather than to shear i n an inclined plane. Under compressive stress the failure of the specimen would start, either on the outer part near the surface or as a result of unfavourable positioning of the particles inside. I t can be se'en i n the figure that the particles at A may be held l a t e r a l l y from the outside by their neighbours, but the particles at B. have no neighbours to hold them, and therefore must be held by tension i n the paste between them. Failure w i l l occur when the tension stresses developed reach the ultimate tension stress of the paste matrix. Indications that the cause of failure of concrete and mortar specimens loaded i n axial compression only, may be due to other causes rather than shear on an inclined plane, are given by the results obtained i n a series of experiments conducted at the University of Washington ( 6 ) . In tests conducted on 4-inch by 8-inch cement-mortar cylinders, i t was found that for large late r a l confining pressures (800 to 2400 lb per sq in) , the failure i n compression was due only to sliding action on a diagonal plane, and that the cohesive and compressive strengths and the angle of internal f r i c t i o n were i n accordance with Mohr's theory of stress. I t was also found that with l i t t l e or no l a t e r a l pressure the failure took the form of spl i t t i n g of the sides with the formation of a cone at either end, and the stresses developed did not f i t the trend of the Mohr's circles. V I f the wedging action of the particles of aggregate i s the cause of failure i n compression of the specimens axially loaded only, the following would be significant factors: a.) The modulus of e l a s t i c i t y of the grains compared to the cement paste. The higher the modulus of the aggregate, the lower the strength of the specimen. b) The shape of the particles and their mutual arrangement. Their arrangement i n a more closely packed and wedge-like manner would result i n weaker specimens. To investigate these factors, inclusions of two materials (glass and steel) with different moduli were used, placed i n various patterns. P a r t 1 MAKING OF SPECIMENS A) COMPOSITION AND PREPARATION OF THE CEMENT PASTE AND MORTAR USED a) Reasons f o r P r o p o r t i o n s I n order to make specimens whose r e s u l t s cou ld be compared i t was dec ided to use the same mix throughout t h i s s tudy . I t was d e s i r a b l e t o o b t a i n a mix f l u i d enough to be workable but w i t h a minimum o f water thereby r educ ing i t s escape when i t was pressed i n the forms, and r educ ing shr inkage o f the paste w i t h i t s i nhe ren t p o s s i b i l i t i e s o f c r a c k i n g . I t was a l s o impor tan t t o use the same water cement r a t i o i n the making o f mor ta r , t o observe the e f f e c t o f aggregate on s t r e n g t h . The p ropo r t i ons o f the mix chosen f u l f i l l e d the above requirements and were: P o z z o l i t h Water Cement Ottawa Sand f o r cement pa s t e : .003 .24 1 f o r mor ta r : .003 .24 1 2 b) B r i e f D e s c r i p t i o n o f the Components i ) " P o z z o l i t h " i s the t rade name f o r a d i s p e r s i n g agent f o r p o r t l a n d cement, c o n t a i n i n g c a l c i u m l i g n o s u l f a t e as the b a s i c i n g r e d i e n t . The d i s p e r s i n g agent i n c r e a s e s the degree o f h y d r a t i o n o f the cement and the p l a s t i c i t y o f the mix , making i t p o s s i b l e t o mix the paste w i t h l e s s wa te r . T h i s reduces the escape o f water from the forms when the specimens are be ing molded, and decreases the number o f v o i d s r e s u l t i n g from the e v a p o r a t i o n o f the water not 2 used i n the hydration process. i i ) Elk Cement, from the British Columbia Cement Company Ltd., Victoria, was used. i i i ) Standard Ottawa Sand #20-30 was used i n a l l mortar specimens. It i s natural quartz, sand from Ottawa, 111., screened to pass a No. 20 sieve and to be retained i n a No. 30 sieve. c) Mixing The paste was mixed i n circular watertight metal pans three and a half inches deep. A pan nine inches i n diameter was used to mix quantities of paste with up to 750 grams of dry materials. For batches with more solid matter pans eleven inches i n diameter were employed. Five inch masons' trowels were used to knead the paste. Two trowels were used, one to scrape the other when necessary, thus avoiding contact with the hands. A l l the materials for each batch were carefully measured. The proportions of cement, sand and Pozzolith were weighed i n grams and the quantities of water measured i n m i l l i l i t r e s . One scale was reserved for Pozzolith and another one for cement and sand. The dry materials were placed i n the pan, mixed thoroughly, and a crater was formed i n the centre into which the water was poured. Once the water was poured, the material on the outer edge was turned into the crater and the whole vigorously mixed with one trowel which was frequently scraped with the other to ensure good mixing of the paste. I t was found 3 that ten minutes of vigorous kneading gave a thorough mixing, and there-fore this period was kept as the time of kneading throughout. It was noted that i f the paste was allowed to set for ten or fift e e n minutes after mixing, i t was easier to place i t i n the forms and more uniform specimens were obtained. This time was given over to oi l i n g and preparing the forms. Bi) TYPES OF SPECIMENS USED. This study was made on tension briquets and compression cylinders. a) Identification and marking of the specimens. The specimens were identified by one letter and two numbers. The mark of identification on top of each specimen was made with ordinary black pencil. The letter and the f i r s t number identified the series to which the specimen belonged, the last number showed the individual number of said specimen i n i t s series. The meanings of the letters remained constant throughout. They weret Tension Specimens A: Briquets with shiny glass plate inclusions B: Briquets with frosted glass plate inclusions Ct. Neat cement briquets E: Briquets with two steel balls as inclusions F: Briquets with one steel plate as inclusion Gr. Briquets with one cork b a l l as inclusion H: Briquets with glass b a l l inclusions Compression Specimens At Cylinders with inclusions of glass balls, not frosted. ° Pattern II,, f i g . 7 B:, Cylinders with inclusions of frosted glass balls, placed i n the same manner as i n cylinders "A". Ct. Neat cement cylinders. Et Cylinders with rows of steel balls placed i n the same manner as i n cylinders "A". Ft- Cylinders with steel b a l l inclusions. Pattern I, f i g . 7 Js Cylinders with glass balls arranged the same way as steel balls i n cylinders "F". K:-. Cylinders with only one central column of steel balls. Pattern IV, f i g . 7 Lt Cylinders with only one central column of steel balls. Pattern III, f i g . 7 Mt Mortar cylinders. b) Tension Specimens were standard briquets with one inch by one inch cross-section at the neck, as seen i n f i g . 1. c) . Compression specimens were standard cylinders 2-inch by A-inch, .(.fig.A) Forms Tension Specimens Standard bronze gang molds as seen i n photograph # 1 were used to make briquets. The forms were placed on smooth-surfaced steel plates (12" x 5" x 1/8"). The interior of the forms and upp_er surface of the plate were covered with a thin coat of mineral o i l (SAE # 20) to prevent adhesion between metal and paste. The o i l i n g was done carefully to put only the right amount; an excess of o i l i f mixed with the paste, would have affected the properties of the specimens. Compression Specimens Standard bronze forms (photograph # 2, "A") for 2" x A" cylin-ders were used. They were set on glass plates (9" x 3" x 1/4") (Photograph # 2 "B"). To prevent displacements of the bronze form on the glass, during the manufacture of specimens, i t was inserted i n the groove of the wooden platform (Photograph # 2 "C") and kept i n place by means of a steel wedge. The bronze form i n i t s turn, was held i n place on top of the glass with paper wedges as shown i n Photograph # 3. Two metal clamps attached to the bronze mold are seen i n this photograph; they are of the band and bolt type and their purpose was to tighten the molds so that the mixing water would not escape during molding and also to prevent separation of the ends of the forms caused by the tamping down of the paste inside them. 6 The forms and plates were covered with a thin layer of mineral o i l to prevent their adhesion to the cement paste or mortar. C) DESCRIPTION OF THE DIFFERENT KINDS OF INCLUSIONS AND OF THE  PROCEDURES FOLLOWED TO CLEAN THEM BEFORE USE. a) General. The object of this work, as has been mentioned before, was to study the mechanism of failure i n compression of neat cement and mortar, and for this purpose numerous compression specimens were studied. In order to investigate their failure, mortar and concrete specimens were imitated by neat cement cylinders with inclusions placed at w i l l reproducing the action of the aggregate. Spherical inclusions of glass and steel were employed. The wedging action, produced by the aggregate, causes tension i n the cement paste and between cement and aggregate. So tension tests were made i n briquets with spherical and f l a t plate inclusions of glass and steel. A study was made of the effect of stress concentration caused by a i r bubbles on tension strengths i n briquets, and for this purpose voids were created at w i l l i n the necks of the briquets by placing there cork balls one-half inch i n diameter. 7 b) Description of the different inclusions used. The following types of inclusions were used in tension specimens i-1) Glass plates, frosted surfaces, 7/8" x 1" x 5/6A" 2) Glass plates, smooth surfaces, 7/8" x 1" x 5/64." 3) Steel plates 7/8" x 1" x l/A" 4) Glass balls, only one in the center of each briquet, diameters of the balls in the neighborhood of 5/8". 5) Steel balls, 5/8" i n diameter, only one i n the center of each briquet. • 6) Steel shapes, obtained by f i l i n g the ends of steel balls with the purpose of placing two side by side i n the neck of each briquet, see figure 2. 7) Cork balls, -g-" i n diameter, one only placed in the neck of each briquet. In compression specimens the only inclusions used were steel balls 5/8" i n diameter and glass balls of various diameters, ranging from .610." to. .640", carefully graded i n order that the variation in their diameters in a given cylinder would be of the order of .005". c) Cleansing of the inclusions. Except in the case of the cork inclusions where the adhesion between the cork and the cement paste was of no consequence, i t was important to obtain good adhesion between the inclusions and the paste. 8 For this reason i t was essential to have the inclusions free from grease, o i l or any other foreign substance. Three different cleansing procedures were tested. Two of them did not prove successful and therefore are worthy only of mention. They vereJ- l ) cleansing the inclusions by immersing them i n carbon tetra-chloride . 2) washing the inclusions thoroughly with soap and hot water and rinsing them i n water. The third procedure, which gave satisfactory results both for steel and glass, consisted of immersing the inclusions i n a solution of hydrochloric acid for about one hour, then rinsing them thoroughly. Afterwards they were l e f t immersed i n water for several hours. Before making the specimens the inclusions were dried i n the a i r at room tem-perature. In order not to s o i l the inclusions, special rubber gloves were used for handling them while they were being cleaned. Frosted glass inclusions Glass inclusions which were frosted with hydrofluoric a d d gave satisfactory results. On the other hand, glass plates which were frosted by being rubbed with emery, powder on another glass, gave very low adhesion between glass and cement. This was probably due to tiny particles of powder which remained on the frosted surface. 9 D) MAKING. OF TENSION SPECIMENS. m) Tension specimens without inclusions. Each briquet was f i l l e d up i n three layers, and each layer was: pressed hard with the thumbs over i t s entire surface area. The pressure of the simultaneous application of both thumbs varied between fif t e e n to twenty pounds. As each form had three briquets, one layer was placed i n each one of the three briquets before proceeding with the next layer i n order to obtain uniform specimens from each mold. When the briquets were f i l l e d up, some paste was heaped above the mold and smoothed off with a trowel. The forms were then taken to the curing room where they were kept for twenty-four hours i n such manner that the upper faces were exposed to the moist a i r but protected from dripping water. b) Tension SpaniTnans with Inclusions. Three different types of inclusions were used i n the tension specimens: 1. - One plate of 7/8" x l " 1 placed at the neck of the briquet. 2. - A single b a l l placed at the neck. 3. - Two balls, side by side placed at the neck. In each case there were two conditions to be fulfilled:., to obtain good contact between the inclusion and the paste, and to place the inclusions i n the right position. 10 Enough paste was placed i n the forms i n the same manner as described for specimens without inclusions, so that when the inclusion was placed i n the briquet the mold was almost f i l l e d up. To achieve good contact between the paste and the inclusion, the l a t t e r had previously been covered with a layer of paste and pressed with the fingers so as to expel, any ai r which might have been trapped. Once the inclusion was i n the briquet, the paste around i t was pressed gently with the thumbs. Then the briquet was f i l l e d up and levelled with a trowel. In this way i t was possible to obtain good results, avoiding the undesirable movements of the inclusions which are l i k e l y to occur i f large pressures are applied to the briquet when the inclusions are already i n place. E) MAKING OF COMPRESSION SPECIMENS. a) Making Cylinders without Inclusions. The paste was placed i n seven layers i n the forms and each layer was compacted with a cylindrical bronze "tamper" (Photograph # 4,, "A"). A layer of cement paste or mortar was placed and compacted i n each one of the jjylinders of the form before proceeding with the next layer. This was done to obtain uniform specimens from each from but also proved to be advantageous because the tamping caused vibrations which smoothed the surfaces of the paste already i n the forms. The paste was placed and compacted i n seven layers i n order to obtain results comparable with the Photograph # 4 . to follow page 10 11 cylinders with inclusions which usually had six or seven rows of inclusions and were compacted before each row was inserted i n position. The paste was compacted by l i f t i n g the bronze tamper "A" (weight 1600 grams) from one half to> one inch above the paste and then letting i t f a l l . This was repeated several times u n t i l the surface of the paste was smooth and even. In the case of cylinders, the convenience of leaving the paste to set for some fifteen minutes after mixing, before beginning to f i l l up. the forms, was more apparent than i n the case of briquets. When this was not done the paste had a tendency to adhere to the bronze tamper creating a vacuum. The result was then a large number of voids and, consequently, poor specimens. The cylinders were f i l l e d up this way to about one sixteenth of an inch from the upper end of the form, then they were taken to the curing room and l e f t there i n such a way that the upper faces were exposed to the moist air , but protected from dripping water. b) Capping. After a lapse of two to four hours, i n order to allow the paste to set and harden to some extent, the cylinders were capped. The cement paste, used for capping, was of the same composition as that used throughout this work. 12 Heaped to a height of approximately l / 8 " , a small amount of paste was placed on top of each cylinder. The heap of the centre c y l i n -der was purposely made somewhat larger than the other two, i n order to prevent trapping a i r when pressure was applied. A clean sheet of glass, l/A" thick, covered with mineral o i l , was pressed on top of the cylinders, avoiding l a t e r a l movement, u n t i l the tops of the three cylinders were smooth and no a i r bubbles or cracks could be observed. Then the cylinders w i t h i n the form, with one glass plate on each end, were returned to the moist closet where they were l e f t for twenty four hours under a load of ten pounds. c) Making of Cylinders with Inclusions. Only one type of i n c l u s i o n was used. Spheres, approximately f i v e -eights of an inch i n diameter, were placed within the cement cylinders with the purpose of imit a t i n g the action of the aggregate i n mortar and concrete. The b a l l s within the cylinders were arranged i n four d i f f e r e n t patterns, as shown i n figure 7 . i ) Manufacture of cylinders with horizontal rows of b a l l s , patterns  I and I I . I . The manufacture of cylinders of pattern I was as follows: 1.- In order to place the rows of b a l l s i n t h e i r correct horizontal positions, v e r t i c a l scales l i k e the ones shown i n F i g . 8 were used, attached to two opposite sides of the bronze tamper "A", with trans-parent • adhesive tape. 13 2 . - Pas te was i n s e r t e d i n the form and compacted w i t h the tamper, so t h a t the upper surface was a t he igh t of l i n e 1. ( F i g . 8 ) . 3 . - The f i r s t row of s i x b a l l s was p l aced above the compacted pas t e , p u t t i n g them i n such manner t h a t a l i n e j o i n i n g t h e i r cen t res would form a symmet r i ca l hexagon. U.- W i t h the tamper, the b a l l s were pushed i n t o the paste u n t i l t h e i r tops came to l i n e 2 . ( F i g . 8 ) . 5 . - Above the b a l l s was pu t a new l a y e r o f paste wh ich , when compacted, came to the he igh t o f l i n e 3, ( F i g . 8 ) . Compacting when there was some paste on top o f the b a l l s gave good r e s u l t s , and d i d no t cause d isp lacement of the i n c l u s i o n s below. 6. - A new row of b a l l s was p l aced on top o f the paste i n such a way t h a t the center of each b a l l was i n a v e r t i c a l l i n e w i t h the middle o f the space between the centers of the b a l l s i n the row below. And then the process was repeated from stage 4 on . The amount of pas te t o be put i n the form p rev ious to the p l a c i n g o f each row o f b a l l s was c a l c u l a t e d w i t h a v i ew to a v o i d i n g c o v e r i n g the b a l l s when they were pushed i n t o t h e i r f i n a l p o s i t i o n . The s c a l e s were a t t ached t o tamper " A " i n an i n v e r t e d p o s i t i o n , so t ha t the p a r t which pro t ruded from the form, cou ld be r e a d . ( F i g . 5 ) . i 4 C y l i n d e r s of p a t t e r n " I I " had the h o r i z o n t a l rows of b a l l s p l a c e d i n such a way t h a t the cent re l i n e s o f the b a l l s i n every row were i n the same v e r t i c a l l i n e s . T h i s i s shown i n both c y l i n d e r s o f photograph No. 6 and i n the cores o f c y l i n d e r s E - 4 and E-5 o f photograph No. 5. S c a l e s s i m i l a r t o those o f the c y l i n d e r s o f p a t t e r n I were used to p l ace the rows o f b a l l s i n t h e i r c o r r e c t h o r i z o n t a l p o s i t i o n s . See F i g . 8. I n the making o f these c y l i n d e r s type " I I " i t was d i f f i c u l t t o keep the b a l l s d i r e c t l y above each o t h e r . Th i s d i f f i c u l t y was s o l v e d by the method i l l u s t r a t e d i n f i g u r e 6, where " F " a r e cement paste wedges ( a l s o seen i n photograph # 4 under "F" ) whose c r o s s - s e c t i o n s are e q u i l a t e r a l t r i a n g l e s w i t h s i d e s approx ima te ly e i g h t e e n - s i x t y f o u r t h s o f an i n c h , made to f i t w i t h i n the grooves o f the tamper mentioned below. These wedges were cas t i n cement forms s p e c i a l l y made f o r t h i s purpose, two days i n advance. I n making the c y l i n d e r s , a l a y e r o f paste o f .27 o r .30 inches was compacted i n the mold . Then the two wedges were p l aced i n p o s i t i o n , be ing kept v e r t i c a l and d i a m e t r i c a l l y opposed by p u t t i n g them adjacent to the v e r t i c a l l i n e s which mark the j o i n t o f the two ha lves of the form. The tamper used (Photograph # 4 . - " A " ) , had two l o n g i t u d i n a l t r i a n g u l a r grooves o f e q u i l a t e r a l c ross s e c t i o n w i t h s i d e s measuring to follow page 14. 15 20/6A"^ two sixtyfourths of an inch larger than those of the wedges.. I t was placed i n the form with the cement wedges f i t t i n g i n i t s grooves, then i t was moved with a vertical motion, the cement wedges acting as r a i l s . Apart from this, the process of manufacture was similar to the one explained for cylinders type "I 1 1. i i ) . Manufacture of Cylinders Type "ITT" pnri "IV". Cylinders type "III" had only one central column i n which the balls were one on top of each other. The procedure followed was basically the same as i n the manu-facture of cylinders type " I " . The balls were centered by sighting through a two-inch hollow pipe f i t t e d at one end with a cross of trans-parent tape. As i n previous cases, scales to determine the horizontal position of the balls were attached to the tamper. Cylinders +.ype "IV" were made following practically the same procedure. The sighting device was used to place the single b a l l i n position. The rows of three balls were carefully placed so that the balls, would be i n the same ver t i c a l line with those above and below them. F) REMOVING THE SPECIMENS FROM THE FORMS, a) Tension Specimens. The briquets were kept i n their molds i n the curing room from 16 twenty to twentyfour hours after being made. Then they were taken out, the clamps of the gang mold loosened, and the supporting metal plate h i t l i g h t l y and repeatedly with a metal rod u n t i l the vibration separated the briquets from the farms. Then they were marked and weighed. b) Compression Specimens. The cylinders were kept i n their forms i n the moist closet with both ends of the molds covered with glass plates. They were taken out from twenty to twentyfour hours later. The glass plates were separated from the paste by hitting them l i g h t l y with a wooden stick on alternate edges of the plate i n such way that the impact did not cause tension between the paste and the plates. After removing the glass plates, the clamps were released and the forms h i t l i g h t l y with a metal rod to separate them from the cylin-ders by means of the resultant vibration. The specimens were then marked and weighed. G). CURING THE SPECIMENS.. Curing i s the process during which the cement paste, mortar or concrete hardens, and the "method of curing" i s the procedure used to obtain this hardening. Two methods of curing were followed i n this study: a.) Curing i n the moist closet b) Steam-curing. 17 a) Curing i n the moist closet. The object of curing the specimens i n moist conditions i s to prevent or replenish the loss of moisture, mostly during the early, relatively rapid stage of hydration. Immediately after removing the specimens from the forms they were returned to the moist closet or curing room. The moist closet is; a tightly closed room where a constant spray of luke warm water keeps a. saturated atmosphere at a temperature of seventy degrees Fahrenheit. The specimens which were cured by this procedure were l e f t i n the moist closet during a desired number of days. b) Stqunr) ynr-Snfr, Steam curing i s a method used to obtain a quicker hardening of the specimens. It consists of keeping the specimens immersed i n steam at 212° F. during a period of five hours. The time of immersion of the samples i n steam and the standard apparatus recommended by the American Society for Testing Materials (5) for soundness tests were adopted. A view of the apparatus i s shown i n photograph #7. The apparatus, a copper container 12" x 2A" and 12" high, was provided with a l i d which could be sealed with adhesive tape. To do the steam-curing, one quarter of a cubic foot of cold Photograph # 7 to follow page la-water was placed inside the container, the samples were placed on a wire rack one inch above the water level and the l i d was put on. Then the apparatus was subjected to the heat of a gas burner. I t took from one hour to one hour and fifteen minutes to bring the water to boi l , and then the boiling was continued for five hours. To raise their temperature gradually, the specimens were placed i n the container when cold. After five hours of boiling, the grooves between the boiler and the l i d were sealed with adhesive tape to keep the inside atmosphere -.• saturated. The apparatus was l e f t to cool at room temperature. After steam-curing some specimens were returned to the moist closet u n t i l they were tested. Others were waxed and dried i n the oven. H) METHOD OF DRYING THE SPECIMENS WITHOUT CRACKING. WAXING. In drying specimens suffer a certain amount of irreversible shrinkage which does not occur simultaneously i n the mass as a whole. As the drying proceeds from the surface inwards, the exterior layers suffer more shrinkage than those near the center of the specimens. This unequal shrinkage produces internal tension and compression stresses with the result that cracks are formed. The cracks formed during this process, of drying w i l l be referred to i n this work, as "drying cracks". "Drying cracks" were observed only i n neat cement, not i n mortar specimens. 19 a) Reasons for waxing. Dr. Alexander Hrennikoff found that by painting the specimens, with wax, drying cracks could be prevented. b) Type of wax.used. The wax "Cerise", recommended by the Baldwin Locomotive Works to cover their SR-4 Strain Gauges when exposed to moisture, gave satis-factory results for temperatures up to 160° F. Above that i t melted and vaporized. The specimens were warmed making the waxing easier. They were then l e f t overnight at an oven temperature of 160° F., i n a i r tight containers with some water to keep them warm and moist. They were kept moist to prevent the formation of incipient cracks. c) Application of the wax. The wax was melted i n a small double-boiler pan, and then applied with an artist's brush. Keeping the water temperature below boiling prevented evaporation of the wax. d) How the briquets were waxed. The only cracks of consequence i n briquets were those formed near their necks, where the stresses were to be measured. Therefore the coat of wax-was applied only at their centers i n a width of approximately one and a half inches. 20 When the briquets were waxed this way, the evaporation of water occured only through the ends and the shrinkage at the necks was uniform. The procedure proved to be satisfactory because none of the neat cement briquets waxed showed any indication of cracking. e) How the cylinders were waxed. On the cylinders, the wax was- applied to form a g r i l l on the surface, with lines of wax approximately one quarter of an inch wide and one quarter of an inch apart. This was done i n order that the water would escape only through the unwaxed windows, placing the i n i t i a l shrinkage i n small squares distributed evenly over the surface, i n this way the shrinkage forces, developed were small and no. cracking took place. X) DRYING THE SPECIMENS a) Process of drying. A study was made of the behaviour of specimens tested i n moist and dry conditions. The samples which were to be tested when moist were either cured i n steam and then stored i n the moist closet or stored i n the moist closet and l e f t there during the required number of days. The specimens which were to be tested dry were cured i n steam, 21 waxed, and then placed i n a thermostatically controlled el e c t r i c oven. It was found convenient to keep the temperature at 160°F. which was just below the melting point of the wax. The specimens dried at this temperature gave satisfactory results not showing cracks or incipient failures which could be due to sudden drying. The specimens were kept i n the oven u n t i l reaching a constant weight. It was noticed that i f the oven temperature was raised or lowered the specimens correspondingly lost or gained weight. The term dry specimens i n this work refers to those that come to a constant weight at 160°F. The weight the specimens lost by being dried at 160°F. was approximately f i f t y per cent of the weight of the water used i n making the paste. The cement paste made from 180 c.c. of water was just enough to make six briquets or two cylinders, consequently each briquet lost approximately fifteen grams and each cylinder forty-five grams. It took from twenty to twenty-five days to bring to a constant weight the neat cement briquets waxed at the necks only, and from thir t y to thirty-five days the neat cement cylinders covered with a g r i l l pattern of wax. As has been mentioned before, drying cracks were observed only i n neat cement, not i n mortar specimens. Consequently mortar specimens 22 were not waxed and the time required by them to come to a constant weight when dried was shorter, from fifteen to eighteen days. b) Precautions before testing dry Specimens. To obtain a temperature uniform throughout their mass the speci-mens after being removed from the oven, were l e f t at room temperature for a period of six to twelve hours. When the temperature throughout the specimen i s not even, the surface i s cooling down faster than the centre and also contracting faster*; thus producing tension stresses near the surface of the specimen. 23 Part 2 TESTING. A) TENSION TESTS. The tension tests were made in a standard tension testing machine which was in accordance with the requirements of the American Society for Testing Materials. The briquets were carefully centered in the clips and the load was applied at a constant rate. The only data to be obtained using this machine was the u l t i -mate tension strength of the briquets, therefore the observations in the different specimens were based on this and on the shape of the failure. The briquets in moist condition were taken out from the curing room immediately before testing, the excess of water being removed from their surface with a clean cloth. As mentioned above dry specimens were left at room temperature from six to twelve hours before testing. The following criterion of the A.S.T.M. (5) was observed in the interpretation of results: "Briquets that are manifestly faulty, or which give strengths differing more than fifteen per cent from the aver-age value of a l l test specimens made from the same sample and tested at the same period, shall not be considered in determining the tensile strength."1 24 B) COMPRESSION TESTS. a) Description of apparatus used. i ) Testing Machine. The compression tests were made on a Baldwin-Lima, Southwark Tate-Emery Universal Testing Machine with a capacity of sixty thousand pounds. i i ) Stress-Strain Recorder. The stress-strain curves were plotted by a Southwark-Templin Stress-Strain Recorder connected to the testing machine. This apparatus was designed to be used on cylindrical specimens two inches i n diameter by four inches i n length and consisted essentially of two parts, the compressometer which was attached to the test cylinder and the microformer type recorder equipment which produced autographic stress-strain records of the compression tests. The function of the compressometer, i n combin-ation with the recorder was to provide a record of load versus specimen deformation measured over a gauge length of two inches. The compresso-meter was comprised of two gauge rings, a heavy base which supported a frame, two pairs of measuring arms and a microformer measuring unit. The compressometer attached to the test cylinder, transmitted through i t s microformer the deformations which were recorded by the gauge to the microformer type recording equipment. The specimen deformation occuring within the gauge length could 25 be recorded at any one of three magnifications: 250, 500 and 1000 to one, when the selector was set in the "Low", "Intermediate" or "High" position respectively. The strain record showed the deformation per inch of gauge length times the magnification ratio. Using always a gauge length of two inches, the intermediate magnification of 500 to one represented specimen strains of .001 inches per inch, and high magnification of 1000 to one represented strains of .0005 inches per inch. Only these two magnification ratios were used in this work. A view of the compressometer is seen in photograph # 8, and photographs #9 and #10 show the compressometer attached to a specimen. Load Maintainer The Baldwin-Lima compression testing machine is equipped with a "Load Maintainer", whose object, as its name indicates, is to maintain a given load for any period of time. b) End Conditions in Compression Tests In compression tests, the stress is transmitted from the heads of the testing machine to the cylindrical sample through the ends of the cylinder. This action of the machine on the test cylinder is important and in many cases responsible for the ultimate strength of the specimen and for its type of failure. The importance of the end conditions has already been realized and studied by several investigators (7). 26 Four different types of end conditions were studied i n the preliminary part of this work. 1. - The ends of the cylinder were carefully lubricated with mineral o i l S.A.E. # 10 and covered with graphite powder. 2. - One layer of thin and soft rubber was placed between each end of the cylinder and the machine. Rubber of about one sixty fourth of an inch i n thickness was used. 3. - One layer of thicker and harder rubber (gasket rubber "Garlock 22", one eigth of an inch thick) was placed between each end of the cylinder and the machine. 4 . - One circular layer of the same gasket rubber (Trade name of gasket rubber used:."Garlock 22") one eigth of an inch thick, confined i n a steel cap of the shape and dimensions shown i n figure 9 was placed at each end of the cylinder. The advantages or disadvantages of these four different types of end conditions were judged by the ultimate strengths of the speci-mens and by their types of failure. The cylinders tested under end Conditions #1 (lubricated ends only) failed by formation of a cone i n one end which s p l i t the rest of the cylinder i n several parts with ve r t i c a l cracks. (Photograph 11). End conditions # 2 and # 3 gave low strengths (from 50 to. 60 per-cent of the strength of similar cylinders tested with condition # 4.). Photograph # 12 a ii A • MJLM Photograph # 13 to follow page 26 27 The specimens fai l e d by s p l i t t i n g as i s shown i n photograph # 12. What rubber was free to flow from the surfaces i n compression, produced out-ward f r i c t i o n forces on the ends of the cylinders. This caused tension on diametrical planes and was responsible for the failure by s p l i t t i n g . Finally, end conditions # 4 (gasket rubber one eigth of an inch i n thickness confined i n circular steel caps), was the one which gave best results. The results were considered more satisfactory because the stresses developed by the specimens were higher, because i n several instances i t could be clearly seen that the failure of the cylinder did not begin at i t s ends, and because larger deformations at failure were obtained. The object of placing rubber within a steel cap was to prevent i t s flow under the pressure, thus avoiding tension at the ends of the specimen. The steel caps were not completely successful i n this because i f the recesses for caps had been made larger than the specimens there would have been a gap between the cylinder and the steel cap where the rubber could have flowed, and i f the diameter of the recesses had been close to two inches the l a t e r a l expansion of the cylinder could have been p a r t i a l l y restricted. By making caps to the dimensions shown, the results obtained were satisfactory, though there was always some flow of rubber and there-fore there was some tension i n the ends and some later a l compression. Apparently, within certain ranges of load, these forces neutralized each other, and i n several instances i t was possible to obtain failures which 28 did not begin at the ends of the specimen. This i s seen i n photograph # 13 showing three cylinders which began f a i l i n g i n the same manner though.they were cured under different conditions: Cylinder C-5-2, steam cured and moist. Cylinder C-7-2, steam cured and dry. Cylinder C-8-3, cured i n moist closet only. c) Types of Failures Presented by Cylinders whose End Conditions at  Testing were Rubber Pads Confined i n Steel Cans. i ) Neat Cement Cylinders. By running the tests slowly i t was possible to stop them at different stages of failure of the specimens. In some instances a. chip came off away from the ends, when a cylinder began f a i l i n g (Photograph # 13); i n most cases however, the failure followed the pattern described below. See photograph # I4. F i r s t one or several cracks appeared i n the cylinder and almost instantly more cracks appeared pointing to the nearest end (Stage l ) , then a whole chip came off (Stage 2), and sometimes (not always) was after-wards enlarged i n the same place (Stage 3). In obtaining failures i n these three stages the loads were removed before the cylinder had reached i t s ultimate strength. I f the load was increased u n t i l the ultimate strength was reached, i n most cases the shape of the failed specimen was that shown i n stage A. After the cylinder had failed i n one side i t failed i n the other side of the same end, leaving a cylindrical base which ended i n Photograph # 1 4 . Photograph #15 - t o f o l l o w page 28 29 a cone with steep sides. Three more failures of this type are shown in photograph # 15. Almost a l l neat cement cylinders tested failed in the described manner, there were several examples of a chip coming out away from the ends and many of stages 2, 3 and four. Only in one case was there a failure which occured in opposite sides of both ends (photograph 16, cylinder C-9-3). i i ) Mortar Cylinders. In mortar specimens the presence of cracks at failure wa3 not as evident as in neat cement cylinders. In every case the failure started at one of the ends of the cylin-der or very near to i t so that i t was never possible to stop the tests before one of the ends was already damaged. When the failure had begun, i t always continued enlarging as i f by crumbling at the plane of failure. In no. case was there formation of cones. Photograph # 17 shows the progressive stages of failure of four different mortar cylinders. C) TESTS OF CYLINDERS IN BENDING. As shall be mentioned later in the interpretation of the results of this work, as the testing of compression specimens proceeded, a hypo-thesis was developed that there were cracks forming in the cylinders during the process of compression previous to their failure. t o f o l l o w page 2 9 30 The transverse bending tests of cylinders were done with the purpose of verifying the presence of such cracks. The two different set-ups of bending-tests devised, are shown i n f i g . 12. There were some tests made with set-up # Z, but the results were not considered reliable because there was no special head of the compression machine by which equal loads could be applied at the two loading points. These bending tests were carried on i n the same machine used for compression tests. D) REPEATED LOADINGS IN COMPRESSION TESTS. Repeated loading i n compression tests did not actually constitute a different type of testing, i t was only a variation of the compression tests which have been described above. Repeated loading is the process i n which a specimen i s loaded to a certain point, unloaded, and loaded again. This same process was re-peated two or more times. In order that the different curves and results of the repeated tests would give comparable results, the end conditions and speed of the machine were kept as constant as possible. Repeated loading was another aid i n investigating the mechanism 31 of failure i n compression. The purpose i n doing i t was to study the sequence of the different curves obtained. E) GENERAL DESCRIPTION OF THE STRESS-STRAIN CURVES OBTAINED IN  COMPRESSION TESTS. a) Shape. Neat cement cylinderst The„general characteristics of shape of the stress-strain curves obtained can be seen i n graph. # 1 , of cylinder C - l - 1 , steam-cured and dry. Neat cement i s not a truly elastic material, i t s graphic stress-strain relation for a continuously increasing load i s generally i n the form of a curved line concave downwards which begins far a l l practical purposes as a straight l i n e . When the loads are increased beyond a. certain point, the stress-strain curve deviates from the straight l i n e , this i s called "flattening of the curve". In some specimens the curve flattened so much that i t was practically horizontal at failure, i n most cases how-ever, failure occured when the curve was s t i l l going upwards. Mortar:. A typical curve i s shown i n graph # 1 9 , of cylinder M - 2 - 9 . Stress-strain curves for mortar were also concave downwards but straighter and steeper than those for neat cement. b) Modulus of El a s t i c i t y . In elastic structural materials subjected to direct tension or compression stresses, within certain limits, the deformation suffered 32. i s proportional to the force applied. This simple linear relationship between the force and the de-formation which i t produces i n a prismatic specimen was f i r s t formulat-ed by the English scientist Robert Hooke and bears his name. Hooke's law i s given by the following equation:. PL. wherei & — total deformation of the specimen E: — Force Applied L — Length of the specimen E — Elasti c constant of the material, called i t s "Modulus of E l a s t i c i t y " . In neat cement and mortar compression tests, only the f i r s t part of the stress-strain curve i s a straight line, indicating direct propor-tionali t y between stress and strain. The i n i t i a l modulus of e l a s t i c i t y "E" also called the "true modulus of el a s t i c i t y " i s the slope of the tangent to the curve at the origin. In this work, when modulus of e l a s t i c i t y i s mentioned, i n i t i a l tangential modulus of e l a s t i c i t y i s meant, unless otherwise stated. For clar i t y and brevity i t w i l l usually be represented by "E". 33 The "secant modulus" or slope of the line drawn from the origin to some point on the curve, i s merely the ratio of stress to total strain. In most tests of this work the i n i t i a l E varied from 1,500,000 to 6,000,000 pounds per square inch. c) How to Obtain the Modulus of E l a s t i c i t y From the Stress-Strain Curves The formula E = PL AS can be written E = P A-e where •€ = & i s deformation per unit length L or unit strain. A l l the graphs presented i n this work correspond to tests on two by four inches cylinders, whose cross-sectional area was: 3.14 s . i . The ordinates of the graphs represent the force P i n kips, and the abscissas the unit strains. Two different scales were used, corresponding to the "intermediate" and "high" magnifications of the stress-strain recording apparatus. In the intermediate magnification each inch of the abscissas i n the graph represents 1000 micro-inches per inch of deformation of the specimen, and i n the high magnification each inch i n the abscissas represents 500 micro-inches per inch, which i s to say that two inches i n the graph correspond to 1000 micro-inches per inch. 3A Therefore measuring the abscissas of the graph i n inches, the following two proportions were found: 1) for intermediate magnification: E = P. _ 1000P A, r x Ar . U000 ; 2) and for high magnification: E = P _ 2000P A, r ~ Ar ^2000 ; i n both cases: r i s the abscissas of the tangent E line, i n inches, d) Creep. Neat cement, mortar and concrete (concrete i s mentioned though i t did not form part of this study) when subjected to loads, i n addition to the instantaneous deformations proportional to the load also suffer "creep" or "time flow". Creep may be defined as the time dependent deformation produced i n solids subjected to stress. In neat cement and mortar i t occurs under constant stress, and at normal temperatures. Therefore the deformation produced by the load may be divided i n two parts: the immediate one which consists of elastic and plastic deformations, and the creep which deve-lops gradually. Under a sustained load, the creep or flow of the material (cement or mortar) continues for an indefinite time. However, i t proceeds at a continuously diminishing rate and approaches an ultimate or limiting value. 35 e.) Effects of the speed of testing. As a consequence of the "creep", the speed at which the test is. run has a considerable effect upon the shape of the stress-strain dia-grams (This effect has been shown by several investigators, see Ref. A, page 61). In this study, these effects were easily detected by running a test at different speeds. When there was a change i n the speed of loading, i t reflected as a change i n the curvature of the stress-strain curve. c Slower speeds of loading produced f l a t t e r curves. The effects of "creep" could be decreased by running the tests quickly. On the other hand, to obtain curves starting smoothly i t was considered advisable to run the tests slowly.(The Baldwing Locomotive Works, Automatic Stress-Strain Recording, Bulletin 162, page 18, #5). To. have comparable results i t was better to run a l l tests at the same speed. The testing machine used does not have provisions to run tests at a constant rate f o r the low speeds of testing which were desired. Therefore, i n order to obtain results as uniform as possible, the tests were run with the same opening of the control valve of the compression machine. The opening was small so that when desired, the load maintainer apparatus could be set with the same opening. f) Shapes of curves of specimens under repeated loading. Both i n neat cement and mortar the curves of cylinders which were loaded several times without bringing them to failure were similar i n 36 shape t o the f i r s t s t r e s s - s t r a i n curve, but the moduli and the creep s u f f e r e d s i g n i f i c a n changes. When the specimens were subjected t o l o a d s w e l l below t h e i r u l t i m a t e s t r e n g t h s , the modulus g e n e r a l l y was h i g h e r i n the second l o a d i n g , and the curve f o r the second a p p l i c a t i o n o f the l o a d more n e a r l y approached a s t r a i g h t l i n e than t h a t of the f i r s t a p p l i c a t i o n . When the f i r s t l o a d i n g was t o a p o i n t near the u l t i m a t e s t r e n g t h of the c y l i n d e r , the succesive l o a d i n g s showed s m a l l e r moduli and s h o r t e r i n i t i a l s t r a i g h t p a r t s of the s t r e s s - s t r a i n curve, making i t apparent t h a t the m a t e r i a l had been i n j u r e d and the p r o p e r t i e s of the m a t e r i a l had been permanently changed. In some cases the secant moduli of the o r i g i n a l and the r e l o a d -i n g curves up to the maximum l o a d o f the f i r s t l o a d i n g , were v e r y s i m i l a r , but t h i s d i d not occur i n every case and t h e r e f o r e can not be g e n e r a l i z e d . In general i t appears t h a t when the neat cement and mortar c y l i n -ders are compressed under a l o a d low enough not t o b e g i n causing f a i l u r e , they present h i g h e r "E" i n the curve of the f o l l o w i n g l o a d i n g , but when the l o a d i s high enough t o produce some i n i t i a l f a i l u r e o f the m a t e r i a l , the moduli become p r o g r e s s i v e l y s m a l l e r . g) Effects of cracks i n the c y l i n d e r s , previous to the t e s t s , i n the  shape o f the s t r e s s - s t r a i n curves. I t was observed t h a t a l l c y l i n d e r s which had t r a n s v e r s e cracks ( e i t h e r as a r e s u l t o f the c o n d i t i o n s o f d r y i n g or produced i n t e n t i o n a l l y O 37 presented s t r e s s - s t r a i n curves wh ich began w i t h an upwards c o n c a v i t y . Such upwards d i r e c t i o n o f curvature cont inued u n t i l the cracks were c l o s e d . C y l i n d e r s which were t e s t e d i n bending f a i l e d suddenly be ing d i v i d e d i n two p a r t s by a crack a t r i g h t angles or i n a s m a l l angle t o t h e i r a x i s . The two p a r t s o f the specimen thus t e s t e d , cou ld be f i t t e d toge ther i n eve ry case and i t was always p o s s i b l e t o t e s t them i n comp-r e s s i o n a f t e rwards . I n every one o f these cases the s t r e s s - s t r a i n curves s t a r t e d concave upwards, sometimes they were v e r y f l a t w i t h s t r a i n s o f .010 o r .015 i nches per i n c h before s t r a i g h t e n i n g o u t . A good example o f t h i s was g i v e n by curves 7A and 7B o f c y l i n -der M-2-2 (graph # 13) t e s t e d i n compression a f t e r bending f a i l u r e . Curve 7A. i s concave upwards and i r r e g u l a r f o r a cons ide rab le l e n g t h , u n t i l a t f ou r t een k i p s the l o a d was decreased s l o w l y down to f i v e k i p s and then i n c r e a s e d a g a i n , the curve ob ta ined then was 7B, s i m i l a r t o curves 1 t o 6, w i t h a t a n g e n t i a l E from 5 t o 9 k i p s w i t h a va lue between the i n i t i a l E o f curves 2 and 3. A l l c y l i n d e r s w i t h i n c l u s i o n s , which were steam-cured and d r i e d , were cracked i n the process o f d r y i n g . The cracks were l a r g e enough to be seen w i t h the naked eye and r u n bo th l o n g i t u d i n a l l y and t r a n s v e r s e l y . When the c y l i n d e r s w i t h rows o f i n c l u s i o n s arranged as i n types " I " and " I I " f a i l e d i n compression, u s u a l l y the p a r t o f the c y l i n d e r w i t h the b a l l s was comple te ly crumbled or so b a d l y cracked t h a t i t was v e r y e a s i l y removed l e a v i n g o n l y the c e n t r a l cores l i k e those shown i n photograph # 5. 38 When the cylinders had been previously dried these central cores broke i n two or three parts under a very slight pressure, but when the cylin-ders had not been dried the central core remained i n one piece even after applying considerable force i n bending. This was taken as an indication that the dry cylinders with inclusions had transverse cracks i n every case. A l l the stress-strain curves of dry cylinders with inclusions were concave upwards at the beginning, as can be seen i n graphs # 16, 17, 18 and 19. When mortar cylinders were loaded to incipient failure and then unloaded, the reloading curves started i n several instances being con-cave upwards, but after some load had been applied became "normal". This fact gave place to the suspicion that cracking had occured, either trans-verse or at such an angle that the cracks could be closed by further application of load. Curve # 6 of graph # 13 (Cylinder M-2-2) gives a good example of this shape or reloading curve. F) INVESTIGATION OF THE BURSTING ACTION OF WATER IN COMPRESSION TESTS OF MOIST SPECIMENS. If two neat cement or mortar specimens are cured under the same conditions and tested respectively wet and dry, the strengths are found to differ. One cause contributing to the smaller strength of wet compression specimens could be a bursting action produced by the water entrapped 39 within i t , not free to flow out when the specimen is compressed. The presence of the bursting action of water was investigated by running tests at different speeds on moist specimens immediately after taking them out of the curing room. If bursting action was. present the quicker tests should give lower results and the sudden failure should reflect in the stress-strain curve. Actually the strengths obtained were higher in the quicker tests where less creep took place, and where free water which could cause failure was not detected in the failed specimens. Escape of water was not observed on the surface of the specimens tested slowly. This summary investigation showed that bursting action does not take place in compression specimens kept in the moist closet. For the purpose of hydration the paste is saturated because the whole cement structure is completely moist, but the specimen as a whole is not satur-ated, a l l the bubbles of air entrapped during the making remain there. The free water which is forced to flow during the compression test can do so freely into the numerous air voids, without producing internal stresses in the specimen. The lower strength of moist specimens is a consequence of phy-sical changes in the cement paste, as i t occurs also in tension tests. This was corroborated by the results obtained in tests of cylinders which were partially dry. 40 Part 3 RESULTS OBTAINED A) TENSION TESTS Tension tests were performed only i n neat cement specimens, and can be divided i n two main groups: briquets without inclusions and briquets with inclusions. 1) BRIQUETS WITHOUT INCLUSIONS In neat cement briquets without inclusions the following properties were studied: Tensile strength of the cement paste when the specimens were steam-cured and dried and when steam-cured and stored i n the moist closet. Relation of strength to age i n briquets which were steam-cured and then stored i n the moist closet. Cracking i n the specimens which were waxed around the neck and dried i n the oven.. The results obtained were also useful as reference for briquets with inclusions made of the same batch of paste and cured under the same conditions and as a means of control for the quality of the paste of compression cylinders made from the same batch. 4 1 The results of tests i n neat cement briquets without inclusions are shown i n tables # 1 and # 2 , for briquets steam-cured and dry and for briquets steam-cured and moist, respectively. a) Meat Cement Briquets Steam-Cured and Dried The results obtained i n the tests performed i n briquets which were steam-cured and dried are shown i n table # 1 . A l l these briquets were waxed around their necks. In table # 1, lines 1 to 5 inclusive show the results of tests performed i n the briquets immediately after they were taken out of the oven. The results, as can be seen, d i f f e r widely from one to another. Lines 7 to 1 4 show the high tensile strength of briquets which were dried to a constant weight at a temperature of 1 6 0 ° F and tested when they were at room temperature. The lower strength of briquet C -5-1 (line 15) which broke at the line between the waxed and the unwaxed parts, indicates that some cracking had taken place there. b) Neat Cement Briquets Steam-Cured and Moist The results obtained i n the tests of this type of briquet are given i n table # 2 . The specimen whose results are to be found i n lines 1 to 1 2 gave higher strengths than the others of the same table. The reason for this appears to be that the atmosphere within the boiler, used to steam-cure Table 1 NEAT CEMENT BRIQUETS, STEAM-CURED AND DRIED WAXED AROUND THEIR NECKS Une S r i f e t tSe S t r 6 4 S S slresf Observations: Number days p.s.i p.s.i 1 C-3-5 5 358 2 C-3-11 5 457 3 C-3-2 6 464 4 C-3-1 6 621 5 E-2-A 7 343 6 G-2-3 7 703 7 C-A-l 21 986* 8 H-lr-1 31 938* 9 C-9-5 37 1153 10 C-9-7 37 1373 11. C-9-9 37 1398 12 C-9-11 37 1439 13 C-9-1 39 1530 U C-9-3 39 1150 15 C-51 45 754 The briquets i n lines 1 to 5 were tested when their temperature was not uniform, 1340.5 * Nbt considered i n the average because i t s strength differs from the average by more than 15$. - to follow page 41 Table 2 NEAT CEMENT BRIQUETS, STEAM-CURED AND MOIST Line Briquet Age Stress Number days p.s.i 1 C-2-1 2 681 2 C-2-3 2 671 3 C-2-4 2 744 A C-2-5 2 726 5 C-2-6 2 749 6; E-l-6 2 753 7 C-l-1 3 786 8 C-l-2 3 850 9 C-l-3 3 882 10 C-l-4 3 774 11 C-1-5 3 748 12 C-l-6 3 798 13 E-4-6 4 607 14 C-3-3 5 576 15 C-3-6 5 558 16 C-3-9 5 483* 17 C-3-12 5 572 18 G-2-6 6 637 19 G-l-6 6 648 20 C-9-13 26 . 747 21 C-6-1 28 677 22 C-6-3 28 619 23 C-6-5 28 653 24 C-9-4 37 675 25 C-9-6 37 684 26 C-9-8 37 689 27 C-9-10 37 676 28 C-9-12 37 645 29 C-9-2 39 629 Average Stress p.s.i 714.2 Observations: The briquets i n lines 1 to 12 were tested when taken out from the boiler, therefore they were p a r t i a l l y dry when tested and that accounts for their higher strength. 806.3 532.3 649.7 666.3 Not considered i n the average. - to follow page 4 1 42 the specimens, did not remain saturated after the boiling was over, even when the grooves between the boiler and the l i d were sealed with adhesive tape. These specimens were tested Immediately after removing them from the boiler and were therefore partially dry, though their loss i n weight must have been small. It is interesting to note the increase in strength resulting from a small amount of drying and also to observe that these briquets did not show indications of cracking, which indicates that the drying cracks do not begin forming at the beginning of the process of drying. Observing lines 13 to 29, i t is seen that the strength of tension briquets steam-cured and moist did show• some increase with age. 2) BRIQUETS WITH INCLUSIONS The purpose in making neat cement briquets with different types of inclusions of glass and steel was to study the adhesion of these materials to the neat cement paste. The data obtained was useful in the interpre-tation of results of compression specimens with inclusions. The different types of inclusions used have already been described. The results will now be presented. Study of Adhesion Between Cement Paste And Glass a) Briquets With Glass Plates Two types of plates were used, frosted and plain. As was mentioned before, the specimens with frosted glass plates gave very low strengths; 43 this i s believed to be due to the way i n which the glass was frosted. A l l the results obtained are shown i n table # 3. Two different sets of briquets with plain glass plate inclusions were made. Both were steam-cured and tested i n moist conditions. In the f i r s t one (Series A-l) the glass used was not cleaned with any special chemical agent. Three of the specimens gave varied results, but the strength of the other three was consistent and had an average value of 567 p . s . i . In the second set of three briquets (Series A-2) the glass plates were cleaned with carbon tetrachloride. The strength of one of the briquets was low, but the other two averaged 535 p . s . i . b) Cement Briquets With Glass Balls The investigation was carried on three different sets of briquets, Series H-l, H-2 and H-3, a l l of them with glass b a l l inclusions whose diameters varied from .625 to .640 inches. Each briquet had one glass b a l l centered i n the neck. Sets H-l and H-2 were made with the purpose of investigating the adhesion between the glass balls and dry cement paste. They were steam-cured and dried. A l l these briquets cracked at their necks and consequently their strengths were very low, never over 150 pounds. Of the nine briquets with glass b a l l inclusions, steam-cured and dried, four had their glass balls s p l i t i n two with the plane of breakage Table 3 CEMENT BRIQUETS WITH GLASS ELATE INCLUSIONS AH, these briquets were steam-cured and tested moist. Observations. Line Briquet Number Age days Strength lb . 1 B-l-1 3 107 2 B-l-2 3 I 4 O 3 B-I-.4 3 80 A B-1-5 3 64 5 B-l-6, 3 131 6 B-2-1 7 323 7 B-2-2 7 B.E. 8 B-2-3 7 259 9 A-.1-1 3 564 10 A-l-2 3 297 * 11 A-l-3 3 B.E. 12 A-I - 4 3 594 13 A-l - 5 3 434* H A-l-6 3 543 15 A-2-1 7 206 * 16 A-2-2 7 501 17 - A-2-3 7 569 Average Strength lb . 567 535 Series (B-l) had frosted glass plate inclusions, which were not cleaned specially before making the briquets. Series (B-2): frosted glass plates cleaned with carbon tetra-chloride Series (A-l): Shiny glass plates, not cleaned specially before making the briquets. Series (A-2): Shiny plates cleaned with carbon tetrachloride. *Not considered i n the average B.E. means:- the specimen was broken while placing i t i n the testing machine. - to follow page 43 44 perpendicular to the axis of the briquet. It appeared that the glass balls had cracked during the process of drying. A third set of briquets, Series H-3, was steam-cured and stored i n the moist closet. The balls i n this case were immersed i n hydrochloric acid and rinsed with water. The results obtained were consistent, a l l within fifteen per cent of their average strength which was 6 1 7 pounds; they are shown i n table # 4 . The area of cement at the neck of these,briquets was 0 . 7 s . i . , and the average strength of comparable neat cement briquets (lines 1 9 to 24, table # 2 ) was 663 p.s.i., therefore the cement paste i n briquets of Series H-3 developed an average strength of approximately 464 pounds and the difference with the total strength indicates that an average adhesion of 5 1 0 p.s.i. did develop between the paste and the glass. This value i s comparable with the adhesion of 5 3 5 p.s.i. obtained between cement paste and glass plates cleaned by immersion i n a solution of hydrochloric acid. II) Study of Adhesion Between Cement Paste And Steel a) Cement Briquets With Steel Plates The f i r s t two sets of six briquets, each Series F - l and F - 2 were steam-cured and kept i n the moist closet, the steel plates were cleaned with carbon tetrachloride. The results showed l i t t l e adhesion, five of the briquets broke while being placed i n the testing machine, three gave strengths below 2 0 0 pounds, and the average of the remaining four was 2 3 8 pounds. Table 4 CEMENT BRIQUETS WITH GLASS BALL INCLUSIONS Curing Conditions!. Steam cured and moist. Inclusions: One glass b a l l centered i n the neck of each briquet. Diameter:; from .625 i n . to .640 i n . Cleaning of the balls: Immersion i n hydrochloric acid and rinsing with water. Number days l b . 1 H-3-1 4 597 2 H-3-2 4 615 3 H-3-3 13 622 4 H-3-4 13 626 5 H-3-5 13 618 6 H-3-6 13 624 617 - to follow page 44 45 A third set of six briquets, Series F - 3 , was also steam-cured and tested moist. In this case the plates were immersed i n a solution of hydrochloric acid and rinsed with water. Three of the briquets gave very low strengths and the average of the other three was 256.6 pounds. Table # 5 shows the results of the tests i n the eighteen briquets of this series. b) Cement Briquets With Steel Balls Three sets of briquets with two steel balls arranged as i n Fig. 2 were made, Series E - l , E-2 and E-4, a l l of which were steam-cured and tested moist. The results are shown i n table # 6. The balls i n the briquets of Series E - l and E-2 had been cleaned with carbon tetrachloride. The balls used i n Series E-4 were cleaned by immersion i n a solution of hydrochloric acid. In the three sets the average strength of the briquets was almost only that developed by the cement paste present at their necks. In the case of Series E - l for example, the average stress i n the paste was of 723 p.s.i., and the average stress of neat cement briquets i n the same conditions (Series G-2) was 714 p . s . i . It i s suspected that the explanation for the small adhesion between steel and the cement paste l i e s i n the fact that i n steam-curing there i s an i n i t i a l separation between the paste and the inclusions. Professor T. Thorvalson (11) found that when cement mortars are subjected to steam-curing, they f i r s t suffer a slight contraction which Table 6 CEMENT BRIQUETS WITH STEEL BALL INCLUSIONS Curing conditionst Steam-cured and moist Inclusions:- Two steel balls placed as i n f i g . 2 Area of steel at neck:. .4872 s.in Area of cement at neck: .5128 s.in Briquet Age Strength Average U n e Number days l b ! Strength Observations. 1 E-l - 1 2 387 Series (E-l), balls 2 E-l - 2 2 347 cleaned with carbon 3 B-l -3 , 2 293* 370 tetrachloride 4 E-l - 4 2 374 5 E-l-5 2 375 6 E-2-1 7 317 Series (E-2) , balls 7 E-2-2 7 322 cleaned with carbon 8 E-2-3 7 338 329.4 tetrachloride 9' E-2-4 7 359 10 E-2-5 7 312 11 E-A-l 7 344 Series (E-4) , balls 12 E-4-2 7 319 cleaned by immersion i n a 13 E-4-3 7 372 355 solution of hydrochloric 14 E-4-4 7 357 acid. 15 E-4-5 7 381 Not considered i n the average. - to follow page 45 Table 5 CEMENT BRIQUETS WITH STEEL PLATE INCLUSIONS Curing Conditionst Steam cured and moist. Steel Plates: 7/8 » x 1 " Average Line f ^ e t A * e Strength S t r e n ^ h Observations Number days lb. it? 1 F-l-1 2 215 2 F-l-5 2 142 3 F-l-3 12 254 4 F-2-3 7 147 5 F-2-5 7 78 6 F-2-4 30. 220 7 F-2-6 30 263 $ F-3-1 4 61 9 F-3-2 4 78 10 F-3-3 4 120 11 F-3-4 4 273 12 F-3-5 4 248 13 F-3-6 4 249 256.6 Series (F-l): Plates cleaned with carbon tetrachloride Series (F-2): Plates cleaned with carbon tetrachloride Series (F-3): Plates immersed i n hydrochloric acid. Not considered in the average. (F-l-2), (F-l-4), (F-l-6), (F-l-2), (F-2-2) failed while being placed in the testing machine. - to follow page 45 46 i s f o l l o w e d by a subsequent expansion. I n the case of specimens w i t h i n c l u s i o n s , t h i s i n i t i a l c o n t r a c t i o n of the paste may cause separations between the m a t r i x and the i n c l u s i o n s . This suggests t h a t a b e t t e r procedure of c u r i n g the specimens f o r i n v e s t i g a t i o n of adhesion between cement paste and other m a t e r i a l s could be by storage i n the moist c l o s e t o n l y , t e s t i n g them while moist. I l l ) Conclusions From Tension Tests i n Specimens With I n c l u s i o n s 1) I t was not p o s s i b l e t o d r y b r i q u e t s w i t h i n c l u s i o n s without o c c a s i o n i n g " d r y i n g c r a c k s " . The reason was the c o n t r a c t i o n of the paste while the volume of the i n c l u s i o n s remained constant. 2) Of a l l procedures t r i e d , the best way t o c l e a n the i n c l u s i o n s from o i l and grease was immersion i n a s o l u t i o n of h y d r o c h l o r i c a c i d , r i n s i n g them afterwards w i t h water. 3) STUDY OF STRESS CONCENTRATION AROUND VOIDS The s t r e s s e s developed i n e l a s t i c m a t e r i a l s subjected t o t e n s i o n or compression, when there are holes i n the s e c t i o n subjected t o s t r e s s , are not uniform over the net c r o s s - s e c t i o n but higher s t r e s s e s occur i n the immediate v i c i n i t y of the h o l e s . This phenomenon i s c a l l e d s t r e s s c o n c e n t r a t i o n . 4 7 Investigations of stresses around a small circular hole i n a rectangular plate subjected to tension under elastic conditions have shown that the distribution of stresses over the cross-section through the centre of the whole occurs as i n Fig. 10 (6). The stresses are highly localized at points "m" and "n,,:, where Omlai - 30o , and decrease rapidly with the increase i n the distance from these over stressed points. 0o i s the uniform stress at the ends of the plate. It was interesting to know the extent to which the presence of a i r bubbles affected the strength and behaviour of tension and compression specimens. To investigate i f strength i s affected by possible concentration of stresses around voids i n neat cement briquets (brittle material) subjected to tension, i t was necessary to be able to produce holes or voids at w i l l . This was done by placing cork balls i n the necks of the briquets. The cork decays during the curing process, not having appreciable tension strength when the tests are performed. Two sets of briquets were made, with cork balls one half inch i n diameter placed at their necks. In set G-l the balls were centered at the necks, i n set G-2 they were purposely placed off-centre. * Both sets of briquets were cured i n steam and then kept i n the moist closet for six days. The resulting strengths are l i s t e d i n table # 7. It can be seen that i n series G-l the strength of a l l briquets was within f i f t e e n per cent of their average; i n series G-2 only one was not taken into consideration. 48 a) B r i q u e t s G - l . W i t h the Cork B a l l s Centered i n T h e i r Necks The average s t r e n g t h o f these b r i q u e t s was 600 pounds, and the a rea o f cement a t t h e i r necks was 0 .804 s . i . , the s t r e s s on the cement was then 696 p . s . i . . T h i s i s o f a h ighe r s t r e n g t h than average 636 p . s . i . i n the neat cement b r i q u e t s t e s t e d under s i m i l a r c o n d i t i o n s ( l i n e s 14 t o 30, t a b l e # 2). The e f f e c t o f s t r e s s c o n c e n t r a t i o n would have been to make the b r i q u e t s c o n s i d e r a b l y weaker, but i n s t e a d those o f S e r i e s G - l were somewhat s t ronge r . Th i s i n d i c a t e s t h a t l i t t l e o r no s t r e s s c o n c e n t r a t i o n must have taken p l a c e . Photograph #18 shows the s i x b r i q u e t s o f S e r i e s G - l a f t e r they were t e s t e d . I t can be seen t h a t the cork b a l l s were f a i r l y w e l l cen te red . b) S e r i e s G-2. B r i q u e t s W i t h Cork B a l l s P l aced Of f - cen t r e a t T h e i r Necks I n the s i x b r i q u e t s of S e r i e s G-2, the cork spheres were p l a c e d to one s i d e o f the neck as can be seen i n photograph #19. The purpose o f t h i s was t o have e c c e n t r i c l o a d i n g t o i n v e s t i g a t e the presence o f s t r e s s c o n c e n t r a t i o n i n t h i s case . The s t reng ths developed are l i s t e d i n t a b l e # 7. To o b t a i n the maximum s t r e s s , the bending moments due to the e c c e n t r i c i t y o f the l o a d i n g caused by the presence o f the ho le o f f - c e n t r e , were cons idered and the f o l l o w i n g formula f o r maximum s t r e s s was used : Table 7 CEMENT BRIQUETS WITH CORK BALL INCLUSIONS Curing Conditions: A l l specimens steam-cured and moist. Inclusions: One cork b a l l " i n diameter placed i n the neck of each briquet. Line piquet Age Strength strength Observations. Number days lb. Average rengl l b . 1 G-l-1 6 545 2 G-l-2 6 5 2 5 3 G-l-4 6 537 4 G-l-5 6 5 9 2 5 G-l-7 6 611 6 G-l-8 6 548 7 G-2-1 6 421 3 G-2-2 6 363 9 G-2-4 6 285* 10 G-2-5 6 430 11 G-2-7 6 402 12 G-2-8 6 332 559.66 389.6 Series (G-l): One cork b a l l centered i n the neck of each briquet. Series (G-2)r One cork b a l l off-centre i n the neck of each briquet. Not considered i n the average. - to follow page 48 to follow page 48 49 f = _P_ + Mc A I To find the bending moment "M", the distance from the neutral axis to the line of maximum stress "c", and the moment of inertia of the cross section with respect to i t s neutral axis, the following calculations were made: Position of the Neutral Axis (Fig. 3) Area of the neck: 1 s . i . Cross sectional area of a b a l l : r 2 = ( l / 4 ) 2 = 0.19635 s . i . . Distance from N.A. to axis A-A: = K . 5 ) - (.19635)(.75) = 0.439 0.44 i n . 1. - .19635 d o A Section I di s t . to d 2 Area Ad 2 I Neutral A. s . i . BH3 = .0833 .06 .0036. 1 .0036 .087 12 _pi = .00307 .31 .0961 .1963 .01898 .023 64 .8037 .064 Distance from the N.A. to the points of maximum stress: c = .5 + .06 = ,56 50 The average strength of the briquets of Series G-2, not considering G-2-4 was 389.6 pounds. The T n g T r i T t r m n stress using the formula above mentioned was: f = 389.6 + (-06H 389.6H.56) = 689.5 p . s . i . .8037 .06A-As i n the case of Series G-l the value of this average stress was somewhat larger than that of briquets without voids, indicating l i t t l e or no stress concentration which could have affected the strength. B) COMPRESSION TESTS Compression tests were performed with twelve different types of specimens, as l i s t e d below. In the l i s t that follows, the patterns of specimens with inclusions refer to the patterns described i n Part 2. As has been mentioned before, the inclusions were either steel balls five-eighths of an inch i n diameter or glass balls with diameters ranging from .610 inches to .640 inches, but graded so that the variation i n diameters was of the order of .005 inches i n any given cylinder. Types of Cylinders Tested 1) Neat Cement Cylinders, steam-cured and dry. 2) Neat Cement Cylinders, steam-cured and moist. 3) Neat Cement Cylinders, cured i n the moist closet only. 4) Mortar Cylinders, steam-cured and dry. 51 5) Mortar Cylinders, steam-cured and moist. 6) Cement Cylinders, steam-cured and dry, with glass inclusions placed as i n pattern I I . 7) Cement Cylinders, steam-cured and dry, with glass inclusions placed as i n pattern I. 8) Cement Cylinders, steam-cured and dry, with steel inclusions placed as i n pattern II. 9) Cement Cylinders, steam-cured and moist, with steel inclusions placed as i n pattern I I . 10) Cement Cylinders, steam-cured and moist, with steel inclusions placed as i n pattern I. 11) Cement Cylinders, steam-cured and moist, with steel inclusions placed as i n pattern III. 12) Cement Cylinders, steam-cured and moist, with steel inclusions placed as i n pattern IV. 1) COMPRESSION TESTS IN NEAT CEMENT CYLINDERS STEAM-CURED AND DRY A total of sixteen cylinders which can be grouped under this heading were studied. Four cylinders were tested during the investigation of the end conditions. Two other cylinders were tested when they were not com-pletely dry, and the remaining ten cylinders were tested dry, with the standard end conditions previously stated. 52 Cylinders Which Were Partially Dry Two cylinders were tested with the purpose of having an indication of the increase of the strength of the cylinder with the increase of the degree of dryness. The result of the tests on these two cylinders showed that, as was to be expected, there is a relationship between the degree of dryness and the strength of the cylinders. This investigation was not carried further and the results of the tests performed in these two specimens are shown in the,first two lines of table # 8. They were compared with the results of the third cylinder of the same series, C-3-3, which are in the fourth line of the same table. a) Age-Strength Relation The ten cylinders studied are listed in order of increasing age in lines 3 to 12 of table # 8. It can be seen that neither the strengths, moduli of elasticity or deformations appear to bear a relationship to the age of the cylinders, therefore, these results indicate that when the specimens are dried their characteristics of strength, modulus of elasticity and maximum deformation are independent of their ages. A similar result in regard to strength was obtained i n tension specimens, as was mentioned before. b) Relation Between the Initial Modulus of Elasticity and the Shape of  the Stress-Strain Curve Table # 9 was prepared to study the relation between the i n i t i a l modulus of elasticity and the shape of the curve. The third column gives the i n i t i a l moduli of elasticity of the different cylinders arranged i n Table 8 NEAT CEMENT CYLINDERS, STEAM-CURED AND DRY. Line Age Drying F f e F £ l u r e _ * , S t a f n Cylinder ^ of Load Stress I n i t i a l J ^ r . u a j r o w u w j . u i . Loadings kips k.s.i. k . s . i . i n ^ i n 1 C-3-2 15 not waxed 1 38.670 12.310 2940 .00530 2 C-3-1 19 not waxed 1 41.700 13.270 2980 .00555 3 C-4-2 21 not waxed 1 40.250 13.120 3180 .00519 4 C-3-3 24 not., waxed 1 44.650 14.100 3320 .00510 5 C-7-2 32 waxed 1 39.475 12.580 3410 .OO505 6 C-8-6 32 waxed 4 44.000 14.000 406O .00525 7 C-8-1 33 waxed 2 42.750 13.600 4300 .00540 8 C-7-5 34 waxed 2 39.600 12.600 3090 .00478 9 C-7-8 34 waxed 1 a . 500 13.200 3230 .00545 10 C-l-1 41 waxed 1 43.500 13.850 3747 .00492 11 C-l-3 54 not waxed 1 42.825 13.640 3280 .00565 12 C-l-6 71 waxed 1 42.400 13.500 3820 .00465 Averages: (lines 3 to 12) 42.095 Line Cylinder Table 9 NEAT CEMENT CYLINDERS, STEAM-CURED AND DRY E i n i t i a l k . s . i . E f i n a l k.s.i. Curve Straight kips Failure Failure Load kips Stress k.s. i . Strain at Age Failure days i n / i n 1 C-7-5 3130 1965 17.0 39.600 12.600 .00478 34 2 C-7-8 3230 1445 11.0 41.500 13.200 .00545 34 3 C-l-3 3280 1200 14.5 42.825 13.640 .00565 54 4 C-3-3 3320 1910 12.0 44.650 14.100 .00510 24 5 C-7-2 3410 1930 9.0 39.475 12.580 .00515 32 6 C-l-1 3747 1850 8.5 43.500 13.850 .00492 41 7 C-l-6 3820 1975 6.5 42.400 13.500 .00465 71 8 C-8-6 4060 2270 6.0 44.000 14.000 .00525 32 9 C-8-1 4300 1637 4.0 42.750 13.600 .00540 33 Averages:.. 42.300 .00515 - to follow page 52 53 order of increase, and the fourth column gives the length i n which the curve remained straight. For convenience this length i s measured with reference to the ordinates of the stress-strain diagram. Table # 9 indicates that there exists a relationship between the i n i t i a l modulus of e l a s t i c i t y and the length for which the curve remains straight. The higher the i n i t i a l modulus, the sooner the curve begins deviating from the straight l i n e . c) Relationship Between the Process of Drying the Specimens and the  Shape of the Curve Of the twelve specimens l i s t e d i n table # 8, five were not waxed and a l l the others were. The stress-strain curve of cylinder C-l-1 (Graph # l ) i s typical of the cylinders which were waxed when dried. The curves of cylinders which were not waxed started by being concave upwards. See graph # 2 for cylinder C-3-1. This characteristic was common to four of the five cylinders which were dried without waxing. The f i f t h cylinder, C-3-3, showed irregularities i n the beginning of the curve which do not reveal the direction of the i n i t i a l curvature. A l l the cylinders which were waxed had curves which started concave downwards. This observation indicates that cracking occurs i n neat cement cylinders which are dried i n the oven, though the cracks either do not come to the surface, or are too small to be observed with the naked eye-i t also indicates that waxing the cylinders as was done i n this work i s an appropriate procedure to prevent the formation of "drying cracks". 54 d) Observations on the I n i t i a l Mr>d"1,i, of E l a s t i c i t y . Strength. Shape of Failure and Deformation of Drv Neat Cement Cylinders i ) The observations on the moduli were made on a l l the specimens of table # 9 . It was considered that the cylinders C-l - 3 and C-3-3 which were not waxed could be included because the upward concavity of curve C-l - 3 i s very small and none i s shown by curve C-3-3. The i n i t i a l moduli of e l a s t i c i t y varied from 3130 to 4300 k . s . i . The E at failure was i n a l l cases but one from I4OO to 2000 k.s.i., the only exemption was cylinder C-l - 3 which had the largest deformation of the group. Its modulus of e l a s t i c i t y at failure was 1200 k.s.i., and i t s total deformation .00565 inches per inch. i i ) Cylinders steam-cured and dry had the highest strength at failure of a l l types of cylinders studied. Their average i s used as the standard to which the strengths of a l l other types are compared i n this work. The average strength of the cylinders of table # 9 was 42300 pounds (13470 p . s . i . ) . The maximum variation from the average, above or below was only 6.7 per cent. This indicates that this group had a very even strength. i i i ) The shape of the failure of a l l the cylinders of this group was considered normal for neat cement cylinders tested with confined rubber for end conditions. There was one cylinder whose failure was away from the ends (C-7-2, photograph 13)j four cylinders whose test was stopped 55 at what can be considered stages 2 and 3 and the tests of three remaining cylinders were continued u n t i l stage four. (See photograph I4). iv) The deformation of cylinders of table # 9 has an average value of .00515 inches per inch. The variation i n deformation of the different specimens i s not large. I t i s 9.7 per cent i n either direction. e) Observations on Repeated Loading of Dry Heat Cement Cylinders Only the cylinders, C-8-1 and C-8-6, were tested i n repeated loading. The/observations which follow were made on the graphs of those two specimens alone and therefore must not be considered general. See graph # 3 for cylinder C-8-6. 1) The reloading curves have lower i n i t i a l modulus of el a s t i c i t y than the curve of the f i r s t loading. 2) In each successive reloading there i s a longer straight part of the curve. 2) MEAT CEMENT CYLINDERS. STEAM-CURED AND MOIST Eighteen cylinders which were steam-cured and kept i n the moist closet were tested. Nine of these cylinders were tested with a single loading and nine were tested under repeated loading. Apart from these, four cylinders steam-cured and moist, had been tested previously i n the investigation for end conditions. 56 a) Age-Strength and Age-Modulus of E l a s t i c i t y Relations i n Steam-Cured Moist Cylinders The results of the strengths and i n i t i a l moduli of e l a s t i c i t y obtained i n the tests performed i n ten of the specimens with the "standard" end conditions are given i n table # 10, where the specimens are l i s t e d i n order of increasing age. Curves "A" and "B" of Fig.13 were drawn joining the average values of the strengths of cylinders at the ages of six, eight, fourteen and thirty-two days. They indicate a continuous increase of strengths and moduli of e l a s t i c i t y . It i s to be noted here that three cylinders, after being steam-cured, were l e f t inside the sealed boiler for approximately sixteen hours, and then were tested. They had higher strengths than those l e f t i n the moist closet for some days after being steam-cured. I t appears that a certain amount of drying had taken place as i n the case of tension specimens. For this reason these three cylinders were not included i n table # 10 or i n Fig. 13. *>) Results of Tests. Stress-Strain Curves of Steam-Cured Moist Cylinders I) Single Loading Case I-a) Cylinders Tested When Taken Out From the Boiler These cylinders were not saturated with moisture. Graph # A for cylinder C-2-2 can be considered representative of the tests performed on the three cylinders i n this condition. Table 10 NEAT CEMENT CYLINDERS, STEAM-CURED AND MOIST A Number Failure Failure Line Cylinder d ^ y g of Load Stress Loadings kips k.s.i. E Strain at i n i t i a l Failure k.s . i . i n / i n 1 C-9-1- 6 8 23.300 7.410 2400 .00422 2 C-9-2. 6 2 22.550. 7.170 2590 .00470 3 C-5-1 8 1 26.000 8.270 2750 .00518 4 C-5-2 8 1. 24.050 7.650 2790 .00465 5 C-6-1 14 1. 27.570 8.760 3120 .00490 6 C-6-2 14 1 29.100, 9.250 2800 .00530 7 C-9-3 14 9 28.600 9.100 2730 .00480 8 C-7-3 30 1 33.400 10.630 2860 .00530 9 C-7-6 32 2. 35.625 11.330 3200 .00560 10 C-7-9 32 4 35.450 11.280, 3330 .00515 - to follow page 56 57 In the three cases they had very large strains at failure as compared with a l l the other tests of neat cement specimens, dry and moist. The average strain of the three tests was .00658 in . / i n . , and the strain of C-2-2 whose graph i s shown was .00775 i n . / i n . . Another characteristic peculiar only to these three specimens among a l l neat cement cylinders, was that the stress-strain curve became very f l a t and i n i t s last part completely horizontal. I-b) Cylinders Kent i n the Moist Closet Before Testing. Single Loading Case. Two graphs, # 5 and # 6, for cylinders C-5-1 and C-6-2, eight and fourteen days old at test, respectively, are presented as good representatives of this group. The stress-strain curves were smooth. The i n i t i a l moduli increased with the age of the cylinders. Older cylinders had straighter curves. The strains at failure were similar, regardless of age. It i s interesting to note i n cylinders C-5-1 and C-6-2 that their i n i t i a l E ' s were very similar (slightly higher i n the older cylinder), their curves were straight at the beginning for approximately the same length and their strains were almost identical. Nevertheless the curve of the younger cylinder was increasingly f l a t t e r after i t deviated from the straight l i n e . Other characteristics of the cylinders of this group were: The stress-strain curve was not f l a t but s t i l l had a measurable modulus of e l a s t i c i t y at fa i l u r e . 58 In cylinders of the same age, the curves with lower i n i t i a l moduli had a larger straight part at the beginning. None of the cylinders tested had graphs starting concave upwards. As i t was to be expected, none of the cylinders showed indications of cracking while curing. II) Neat Cement Cylinders. Steam-Cured and Moist. Tested Under  Repeated Loading In order to discuss the effect of repeated loading on neat cement specimens steam-cured and moist, two graphs are presented. Il-a) Graph # 7 (cylinders C-7-6) is a good representative of the cylinders which were loaded the fi r s t time to a point very near their failure. The second loading curves in these cases had lower i n i t i a l tangential moduli than the f i r s t curve. Il-b) Graph # 8 (cylinders C-9-3) is a good example of specimens which were tested under repeatedly increasing loads, beginning with loads far below their maximum strengths. In this case the i n i t i a l tangential E (measured as near the beginning of the curve as the irregularities permitted) was larger in the successive loadings. One of these cylinders which was loaded the second time to a point near its maximum (C-7-9) had a lower i n i t i a l tangential E in its third curve and s t i l l smaller in its fourth. 59 The two cylinders, C-9-1 and C-9-3, were loaded several times, increasing the load by five kips each time*' Their i n i t i a l B did not vary very much after the second loading until the load came to a limiting value (20 k. in C-9-1 and 24 k. in C-9-3). In the successive loadings the moduli became progressively smaller. II-c) Cylinder C-ll-3 (Graph #9), on which the load was main-tained for one hour in two different tests twenty hours apart, presented peculiarities which are worth mentioning. i) Initial E On the fi r s t test a load of 20.65 kips was maintained for one hour. The second curve had a smaller i n i t i a l E than the f i r s t one and was straight for a longer partj its modulus decreased rather abruptly at around seven kips and from then on the curve was practically straight up to twenty kips, when the load was removed. The specimen was then kept for twenty hours in the moist closet and tested again. This time (curve 3) the i n i t i a l E was higher than the second but smaller than the f i r s t . The curve was straight for approximately six kips. , The secant modulus from zero to twenty kips of curves 2 and 3 i s practically the same, and smaller than the one of curve 1. The fourth test was performed immediately after the third. The i n i t i a l E was very high (even higher than curve 1) and the curve was straight up to five kips, then the modulus decreased abruptly and the curve continued straight to 22.6 kips where the load was maintained. 60 The f i f t h test had a straight curve, except for the beginning, where the upward concavity could be interpreted as meaning that some cracking had already taken place. The ultimate compressive strength of this cylinder was 2A.A5 kips. i i ) Effects of maintained loading. Creep. Two. tests i n which the load was maintained for one hour were made on this cylinder, the second one approximately twenty hours after the f i r s t . The progress of the creep was observed i n both cases several times during the hour and the results are shown i n the graphs of f i g . IA;; curve 1 corresponds to the creep, during the f i r s t time the load was maintained and curve 2 to the second. The following observations were:. 1) Stress-strain curves of tests after the load had been maintained consisted mainly of two straight lines connected by an abrupt change i n curvature. 2) The i n i t i a l E increased after the specimen had "rested" for twenty hours, and, after the second maintained loading, increased to a. value larger than the i n i t i a l E of the f i r s t curve. 3 ) These results may indicate that when a high load (near to the ultimate strength of a cylinder,) which has not produced failure i s maintained, a rearrangement of the cement particles within the cylinder takes place. After that and for loads not larger than 61 the original, the specimen behaves as i f more nearly elastic. Also smaller amounts of "creep" take place when the cylinder i s tested again under maintained loading. c) Strength. I n i t i a l Modulus of E l a s t i c i t y . Deformation and Shape of Failure of Neat Cement Cylinders steam-cured and moist. The strength of the cylinders and their moduli of e l a s t i c i t y increased with their ages. From the tests performed an indication for deformation-age relationship could not be obtained. The average deform-ation of cylinders of table 10 was .0049.8 i n / i n . or 96.7% of the deform-ation of steam-cured dry neat cement cylinders. The shape of failure i n most cases was of the "normal" type, most of the tests were stopped i n stages 2. and 3 (Photograph 14). There were two cases i n which the failure was continued to stage 4, and one case (C-5-2, photograph 13) i n which the test was stopped when only one chip had come out. 3) NEAT CEMENT CYLINDERS CURED IN THE MOIST CLOSET ONLY. These cylinders were not steam-cured, but cured by storage i n the moist closet for thirt y days. Five specimens were tested, which can be divided i n two groups for their study:. Those which were loaded to a high stress i n the f i r s t loading 13 cyls.), and those i n which the load was increased progressively i n repeated loadings. The numerical results of the tests are given i n table 11. Table 11 NEAT CEMENT CYLINDERS CURED IN THE MOIST CLOSET ONLY. Lne Cylinder Age days Number of Loadings Max. Load kips Max. Stress k.s.i. * E I n i t i a l k . s . i . Max. Strain i n / i n 1 C-7-1 30 2 34.250 10.90 4275 .00640 2 C-7-4 30 1 34.500 10.98 3000 .00761 3 C-7-7 30 3 35.500 11.30 3580 .00618 4 C-8-4 30 7 37.500 11.93 irregular .00560 5 C-8-3 30 5 39.100 12.42 4340 .00600 Averages 36.170 11.50 .OO636 - to follow page 61 62 a) The f i r s t group was formed by three cylinders (C-7-1, C-7-4 and C-7-7). The curves of cylinders C-7-1 and C-7-4 are i n graph 10. They were loaded u n t i l they showed indications of failure i n the f i r s t loading, this was above 34 kips. In both cylinders which were reloaded afterwards the curves showed irregularities which indicate that the failure had be-gun during the f i r s t loading. Characteristic of these cylinders and their stress-strain curves, were i ) High strength, average almost the same as that of comparable cylinders steam-cured and moist of the same age. i i ) Large deformations, with a maximum of .00761 i n / i n . and an average of .00673 i n / i n . i i i ) , Moduli of e l a s t i c i t y within a wide range (3000 ksi to 4275 ksi.) and as i n the two types of cylinders previously studied, the curves of specimens with lower i n i t i a l Er.'s were straight i n a longer part at the beginning. iv) Stress-strain curves f l a t near failure. b) The second group was formed by cylinders C-8-3 and C-8-4 loaded five and seven times respectively. See graph # 11. Both cylinders had high i n i t i a l moduli. Higher than a l l other neat cement specimens studied, dry or moist. Cylinder C-8-4 had very nearly the same i n i t i a l modulus i n the successive reloadings, u n t i l a pressure of thirt y five kips was applied, 63 after that the modulus began decreasing. In cylinder C-8-3 the second i n i t i a l E was smaller than the f i r s t , but thereafter the i n i t i a l modulus continued being v i r t u a l l y the same. The fourth loading was up to th i r t y nine kips and the modulus was s t i l l the same i n the f i f t h and f i n a l one. In both cases the straight part of the curve became shorter as the number of loadings increased. The maximum strains were large (average .0058 in/in.) though not as large as i n group (a). In both cases the curve was s t i l l rather steep, at failure. Note:; With regard to the high moduli of e l a s t i c i t y of cylinders C-8-3 and C-8-4 i t i s deemed advisable to point out that the four cylinders of series G-8 which were tested i n compression (two more were tested i n bending only), two steam cured and dry, and two cured i n the moist closet only, had a very high i n i t i a l E. The moist cylinders had a s t i l l higher one than those steam-cured and dry. Failure:.- The tests i n the five cylinders of this group were a l l stopped at different stages of their failure, the shapes of which are shown i n photograph #20. I t can be seen there that failure of cylinder C-8-3 began away from the ends, and the other four specimens gave a very good example of the four stages of "normal" failure for cylinders tested with confined rubber as end conditions. U) MORTAR CYLINDERS STEAM-CURED AND DRY. Only three compression teste were made and their results are i n table 12. Table 12 MORTAR CYLINDERS, STEAM-CURED AND DRY. £_ e Number Max. Max. E Max. Line Cylinder . of Load Stress I n i t i a l Strain y s Loadings kips k.s.i. k . s . i . i n / i n 1 M-2-11 19 6 19.500 * 6.20* A510 * .00170 2 M-2-1 23 6 25.000 7.95 5330 . 00151 3 M-2-9 19 1 27.100 8.62 5680 .00189 Averages: 26.050 8.28 .00170 Not considered i n the average. - to follow page 63 Photograph # 20 to follow page 6 3 6 4 Cylinder M-2-11 was irregular, the observations which follow were made on cylinders M-2-1 and M-2-9, see graph # 12. Dry mortar specimens had a high modulus of e l a s t i c i t y and an almost straight line curve. They had small deformations and lower strengths, than the dry neat cement cylinders. No numerical data i s given here because of the insufficient number of specimens tested. The load was maintained for one hour i n the fourth loading of cylinder M-2-1 and the creep was observed every fi f t e e n minutes; the results are plotted i n curve # 3 of f i g . 14, where i t can be seen that most of the creep occurred during the f i r s t few minutes and increased very slowly thereafter. The irregularities near the beginning of the f i r s t three curves of cylinder M-2-1 did not permit accurate evaluation of the modulus. In the last three curves the modulus shows progressive decrease. Failure t Cylinder M-2-9 failed i n the same manner as most mortar cylinders did when tested with confined rubber, that i s to say by the-sliding of a part of one end with respect to the rest of the cylinder. The plane of sliding was very steep as can be seen i n photograph # 17. In the case of cylinder M-2-1, the upper end showed indications of failure by crumbling after the second loading. Therefore, from then on, the upper end condition was changed to lubrication with o i l and graphite. When failure occurred there was formation of a cone at that end. (See photograph #11) . 6 5 5) MORTAR CYLINDERS, STEAM-CURED AND MOIST. Twelve cylinders of this type were tested i n compression, their ages varying from four to thirt y five days. There was a marked increase i n strength with aging, but the results of these twelve tests were scattered as can be seen i n f i g . 13-C, where the curve shown i s only a rough approximation. Table 13 shows the numerical values of the tests. General characteristics of the stress-strain curves of these cylinders were (see graph # 13)*-i ) Lower moduli of e l a s t i c i t y than mortar cylinders steam-cured and dry. i i ) Nearly straight curves, as i n the case of dry mortar cylinders. i i i ) Reloading curves straighter than the original stress-strain curve. iv) In successive loadings the length of the irregular part at the beginning of the curves increased progressively as the number of loadings increased. Though i t i s not very apparent, i t i s suspected that these irregularities were i n most cases upward concavities of the curves. Three characteristics peculiar to those tests illustrated i n graph 13 came to l i g h t : i j The second i n i t i a l E was higher than the f i r s t , but the second curve had a shorter straight part. Table 13 MORTAR CYLINDERS, STEAM-CURED AND MOIST. ine Cylinder Age days Number of Loadings Max. Load kips Max. Stress k.s.i. E I n i t i a l k.s.i. Max. Strain i n / i n 1. M-3-A A 2 12.080 3.8A 3290 .00175 2 M-3-6 A 2 12.200 3.88 irregular .00115 3 M-3-1 A A 12.800 A.07 irregular .00110 A M-3-2 9 A 17.880 5.68 irregular .00225 5 M-2-A 13 A 18.650 5.93 A980 .00110 6 M-2-10 17 3 15.700 A. 99 A680 .00150 7 M-2-8 18 3 20.000 6.36 A820 .00180 8 M-l-2- 18 1 23.600 7.51 5A00 .00150 9 M-l-1 18 3 2A.900 7.92 irregular .00200 10 M-2-2- 22 8 23.000 7.32 55AO .00222 11 M-2-6 32 2 20.600 6.55 6500 .001A2 12 M-3-3 35 6 72A.000 7.6A 5630 .00160 - to follow page 65 66 i i ) From the third to the sixth loadings the i n i t i a l moduli decreased and the curves were progressively more straight. i i i ) The fir s t curve starts without irregularities, the second curve has a small irregularity at the beginning, and in the successive loadings the same irregularity appears over increasingly larger parts of the curves. It was mentioned before that a l l cylinders which had transverse cracks when tested, had stress-strain curves which started concave up-wards and that such direction of curvature continued until the cracks were closed. The curves 7A and 7B of graph # 1 3 were then given as a good example. A close examination of the irregularities at the beginning of the curves reveals that they are actually upward concavities, as can be clearly seen in the sixth curve. Cylinder M-3-3 which was also loaded six times presented similar characteristics. The behaviour of these specimens corroborates the hypothesis that progressive failure under repeated loading causes cracks, either nearly normal to the axis of the cylinders or inclined at angles such that the cracks close under a new load. Failure,:. Mortar cylinders steam-cured and moist did not f a i l suddenly. They presented an inclined plane of failure which started at one of the ends. In tests which were stopped when failure began, the planes of failure extended to different parts of the sides of the cylinder (see photograph 17). In those where the load was not removed until complete 67 f a i l u r e , the plane of f a i l u r e extended ot the o ther end and i n c e r t a i n cases there was a tendency towards the fo rma t ion of a cone as i n neat cement c y l i n d e r s (see M - 3 - 1 , photograph 1 7 ) . 6) CEMENT CYLINDERS STEAM-CURED AND DRY. WITH GLASS INCLUSIONS PLACED  AS I N PATTERN " I I " . E l e v e n c y l i n d e r s o f t h i s type were made and a l l af them t e s t e d under a s i n g l e l o a d i n g . S i x o f these specimens had s i x rows o f s i x b a l l s each and f i v e had f i v e rows. A l l these c y l i n d e r s had been d r i e d i n the oven and had cracked d u r i n g the process w i t h l a r g e cracks both l o n g i t u d i n a l and t r a n s v e r s e . Dur ing t e s t i n g i t was observed i n s e v e r a l i n s t a n c e s t h a t the t r ansve r se c racks c lo sed under the l o a d w h i l e the f a i l u r e o f the specimen u s u a l l y began by enlargement o f the v e r t i c a l ones. Two o f the s t r e s s - s t r a i n curves are presented , graphs # 1 4 and # 15 f o r c y l i n d e r s B - l - 1 and A - 3 - 2 , upon which the gene ra l c h a r a c t e r i s -t i c s o f a l l o ther s t r e s s - s t r a i n diagrams f o r t h i s type o f specimen can be d e s c r i b e d . S i x of the e l even c y l i n d e r s (marked " R " i n t a b l e 14) had curves s i m i l a r t o the curve B - l - 1 j they a l l s t a r t e d concave upwards, t h e i r E ' s i n c r e a s i n g c o n t i n u o u s l y u n t i l the curves became s t r a i g h t f o r a cons ide rab l e l e n g t h . I n the s t r a i g h t p a r t of the curves the modul i o f e l a s t i c i t y had v a l u e s rang ing from 1890 to 3180 k s i . F a i l u r e was sudden and p rev ious t o i t there was o n l y a s m a l l i r r e g u l a r i t y i n the curve . Table 14 CEMENT CYLINDERS STEAM-CURED AND DRY, WITH GLASS BALL INCLUSIONS PLACED AS IN PATTERN ' I I 1 . A Number of Number Failure E E Max. Line Cylinder Curve g Horizontal of Load I n i t i a l Max. Strain d a 3 r s Rows Loadings kips k.s.i. k.s.i i n / i n 1. A-l-1 I 51 6 1 11.000 C.U. irreg. .00230 2 B-l-1 R 52 6 1 15.980 c . u . 2819 .00250 3 B-l-2 R 50 6 1 14.800 CU. 2438 .00230 A A-4-1 I 48 6 1 20.500 c . u . irreg. .00520 5 A-4-2 R 48 6 1 21.120 c . u . 3300 .00295 6 A-4-3 I 24 6 1 17.800 C.U. irreg. .00225 7 B-2-1 I 77 5 1 9.100 irreg. irreg. irreg. 8 A-2-1 R 77 5 1 II .84O C.U. 1890 .00257 9 A-3-1 R 37 5 1 21.600 C.U. 3180 .00302 10 A-3-2 I 37 5 1 12.400 C.U. irreg. .00295 11 A-3-3 R 37 5 1 15.880 C.U. 3100 .00260 C U. Means that the stress-strain curve started concave upwards. to follow page 67 68 The s t r e s s - s t r a i n curves o f the f i v e remaining c y l i n d e r s p resen-ted c h a r a c t e r i s t i c s s i m i l a r t o t h a t o f A-3-2. (Graph 15). A l l of them s t a r t e d a l s o concave upwards, but i n s t e a d of coming to a l i n e which would remain s t r a i g h t f o r a w h i l e , they began p r e s e n t i n g i r r e g u l a r i t i e s from a l o a d o f f o u r k i p s u n t i l they f a i l e d , as i f the i n c l u s i o n s were b e i n g moved or r ead jus ted suddenly, caus ing the cor responding k i n k s i n the curve . Common c h a r a c t e r i s t i c s o f the e l even c y l i n d e r s were, t h a t t h e i r curves began concave upwards, the f a i l u r e s s t a r t e d by widening of the e x i s t i n g v e r t i c a l cracks and i n every case there was crumbling o f the outer p a r t o f the c y l i n d e r where the rows o f b a l l s were . The s t r eng ths a t f a i l u r e , modul i o f e l a s t i c i t y and u l t i m a t e deformat ion o f these c y l i n d e r s were s c a t t e r e d and v a r i e d over a wide range, as can be seen i n t ab l e # 1J+. Thus no gene ra l conc lus ions cou ld be drawn. Three o f the e l even c y l i n d e r s ( s e r i e s B) were made w i t h f r o s t e d b a l l s w h i l e a l l o thers were made w i t h smooth ones, but no s i g n i f i c a n t d i f f e r e n c e was n o t i c e d due t o the cracks formed i n the process o f d r y i n g . 7) CEMENT CYLINDERS. STEAM-CURED AND DRY. WITH GLASS INCLUSIONS PLACED  AS I N PATTERN " I " ' . S i x c y l i n d e r s , of t h i s type were made, s e r i e s J-2 had s i x rows, o f b a l l s and s e r i e s J - 3 had seven. A l l o f t h e i r s t r e s s - s t r a i n curves are presented i n Graph # 16 and a l l t h e i r numer ica l r e s u l t s i n t a b l e 15. F i v e o f these specimens were t e s t e d under one l o a d i n g o n l y . Table 15 CEMENT CYLINDERS STEAM-CURED AND DRY, WITH GLASS BALL INCLUSIONS PLACED AS IN PATTERN 'I'. . Number of Number Failure E E Max. Line Cylinder , Horizontal of Load I n i t i a l Max. Strain a y Rows Loadings kips k.s.i. k.s.i. i n / i n 1 J-2-1 29 6 1 10.240 3180 3180 .00285 2 J-2-2 30 6 2 9.400 CU. 3030 .00285 3 J-2-3 37 6 1 8.420 c u . 1775 .00220 4 J-l -1 31 7 1 11.000 1795 1795 .00340 5 J-l -2 31 7 1 9.410 Small CU. 2375 .00415 6 J-l -3 37 7 1 8.600 1400 1400 .00160 C.U. means that the stress-strain curve started concave upwards. - to follow page 68 6 9 With these cylinders a study was made of the effects of progres-sive drying and consequently of the effect of the cracking due to drying, on the shape of the stress-strain curve. The only cracks which could be observed with the laboratory f a c i l i t i e s at hand, were those at the surface, therefore the c r i t e r i a to establish i f a specimen had been or had not been cracked was based on the appearance of i t s surface. Series J-2: From paste made with 180 c.c. of water three cylinders of Series J-2 were made, without leftover. Therefore each one must have lost approximately thirty grams when dried. The three cylinders were kept i n the oven under daily observation. Twenty-eight days later cylinders # 2 and #3 began presenting small cracks^ (they had lost 25.2 and 24.6 grams, therefore were 84$ and 82% dry, respectively). Cylinder # 1 had lost 22.8 grams (76$ dry) and did not yet show any exterior cracks. J-2-1 was then l e f t out to be tested and the other two returned to the oven, where they were l e f t u n t i l J-2-2 was t h i r t y days old and 86.4% dry and J-2-3 was thirty-seven days old and 98% dry. The effects of the different degrees of dryness can be observed i n their stress-strain curves, see graph # 16. The curve of cylinder J-2-1 began straight and continued that way u n t i l about seven kips, where the irregularities began. Cylinder J-2-2 was loaded twice, the f i r s t time only up to six kips. Both curves started being concave upwards, but i t i s interesting to note that the concavity i s somewhat smaller i n the second curve as i f 70 the f i r s t loading had closed the cracks to a certain extent. In the second case the curve i s v i r t u a l l y straight from 3.6 kips to 6.4 kips, where i t becomes irregular. The curve for cylinder J-2-3 had a larger upward concavity and was f l a t t e r than the previous ones, i t became irregular at 4.6 kips. The ultimate strengths of these cylinders were 10.2, 9.4 and 8.4 kips respectively. Series J-1: The three specimens of this series had seven rows of balls each. The batch of paste made with 180 c.c. of water was enough to f i l l up the three cylinders, leaving an excess of 90 grams, therefore each cylinder had approximately 54 grams of water of which approximately 27 must have been lost i n the drying process. J-l-1 was 31 days old and approximately 90% dry when tested. Small cracks had begun appearing on i t s surface. Its stress-strain curve started straight and continued that way u n t i l five kips. (Graph # 17). J-l-2 was of the same age but somewhat drier, approximately 91.5%. Its surface was cracked to a larger extent than J-2-1. The curve presented a small upward concavity at the beginning. I t became straight at one kip and irregular at 3.6 kips. Finally, cylinder J-l-3 was tested when 37 days old and approxi-mately 97.5% dry. The cracks on i t s surface were large and could be easily seen. Its curve started rather f l a t i n what could be the beginning of an upward concavity, but i t s irregularities began at a load of two kips, before i t became straight. 71 These cylinders failed at 11, 9.4 and 8.6 kips respectively. Conclusions; In both series there appears to be a definite relation-ship between the extent of the cracking i n the specimen and the shape of the curve. The hypothesis that transverse cracking i n the specimen produces upwards concavity at the beginning of the curve was corroborated. Both series gave indications that the cracking of specimens with inclusions takes place during the last stage of drying as i f most of the contraction of the neat cement paste occurs i n the f i n a l stages of the process of drying. This appears to be an interesting subject for future investigation. The results of the tests of cylinders J-l-1 and J-l-2 seem to indicate that the cracking of the specimen begins at the surfaces and proceeds inwards, i n both cases there were small cracks noticiable at the surface but their curves indicated that very l i t t l e cracking had already taken place. In both series the specimens became weaker as they became drier, and i n both series also, the curves became irregular sooner i n the drier cylinders. In each of the six cylinders there were some glass balls which were cracked when the specimens were removed from the testing machine, but both dry cylinders had a much larger percentage of cracked glass balls (of 36, 26 were cracked i n J-2-3 and of 42, 16 were cracked i n J-l-3). as i f the last part of the drying process could have had effect i n the glass balls, or as i f the transmission of pressures within the specimen was; 72 modified by the amount of cracking or by the hardening of the dryer paste. -It seems more l i k e l y that the glass balls had cracked before the test and this was the reason why the stress-strain curves of cylinders J-l-3 and J-2-3 became irregular under very small loads. Cracking of the glass balls was also noticed i n the drying of tension specimens. 8) CEMENT CYLINDERS. STEAM CURED AND DRY WITH STEEL BALL INCLUSIONS  PLACED AS IN PATTERN "II". Eight cylinders of this type were made and tested, six of them had six horizontal rows of six balls each and two had five rows. Table 16 gives the loads at failure, maximum moduli of e l a s t i c i t y and maximum deformation at failure of the eight specimens. The stress-strain curves of cylinders E-2-3 and E-3-2 are present-ed because they are good representatives of a l l the specimens of this type. (Graphs 18 and 19). In the drying process a l l these cylinders cracked, i n every case they presented six main vertical cracks running lengthwise, each one corresponding to one column of balls. Besides there were i n every case horizontal cracks corresponding to the horizontal rows of balls. The characteristics common to a l l the stress-strain curves of this type of cylinder were:.. i ) A l l the curves started concave upwards. Table 16 CEMENT CYLINDERS, STEAM-CURED AND DRY WITH STEEL BALL INCLUSIONS PLACED AS IN PATTERN "II". Number of Number Failure Average E E Max. Line Cylinder , Horizontal of Load Load I n i t i a l Max. Strain aays Rows Loadings kips kips k.s.i. k.s.i i n / i n 1 E-l - 1 65 6 1 13.910 CU. 1520 .00430 2 E-l-2 64 6 1 11.320 CU. 2005 .00235 3 E-l-3 68 6 1 10.600 CU. 1430 .00410 12.330 4 E-2-1 63 6 1 11.530 c.u. 2470 .00295 5 E-2-2 63 6 1 13.800 c u . 2880 .00294 6 E-2-3 64 6 1 11.090 2860 .00257 7 E-3-1 53 5 1 10.240 10.440 c.u. 1950 .00313 8 E-3-2 53 5 1 10.640 c.u. 3500 .00205 Not considered i n the average C.U. means that the curve started concave upwards. - to follow page 72 73 i i ) None o f the curves were smooth. They a l l had cont inuous s m a l l i r r e g u l a r i t i e s , as can be seen i n graph # 1 8 . C y l i n d e r E - 2 - 3 was loaded t w i c e . The s t r e s s - s t r a i n r eco rde r was i m p r o p e r l y a t t ached t o the specimen the f i r s t t ime so t ha t the curve f o r t h i s l o a d i n g was comple te ly i r r e g u l a r . The second cu rve , a f t e r the r e c o r d e r was r e s e t , was smoother and w i t h a l a r g e r E up to the p r e l o a d i n g s t r e s s , t han the curves o f a l l o the r c y l i n d e r s o f t h i s t y p e , as i f the i n i t i a l l o a d i n g had c losed and ad jus ted the i r r e g u l a r i t i e s . Though the c y l i n d e r s were c racked , t h e i r s t r eng ths were even. I n the group w i t h s i x h o r i z o n t a l rows o n l y E - l - 3 had a s t r e n g t h d i f f e r i n g by more than f i f t e e n per cent from the average . F a i l u r e began by widening o f the v e r t i c a l c racks and then c rumbl ing o f the p a r t w i t h b a l l s . A l l b a l l s were v e r y l o o s e i n t h e i r s o c k e t s , w i thou t adhes ion to the p a s t e . I n most cases the c e n t r a l core o f the c y l i n d e r s remained i n one p i e c e , but was broken i n two or three p a r t s under v e r y s l i g h t p r e s s u r e s . A v a l u a b l e r e s u l t of the bes t o f t h i s type o f c y l i n d e r s i s the shape o f the curve s t a r t i n g concave upwards as a consequence o f the c r a c k i n g . 9) CEMENT CYLINDERS. STEM-CURED AND MOIST. WITH STEEL INCLUSIONS AS I N  PATTERN " I I " F i v e c y l i n d e r s o f t h i s type were t e s t e d . The r e s u l t s are l i s t e d i n t a b l e # 17 . Two specimens (Se r i e s E - A ) had s i x h o r i z o n t a l rows o f b a l l s Table 17 CEMENT CYLINDERS, STEAM-CURED AND MOIST, WITH STEEL BALL INCLUSIONS PLACED AS IN PATTERN »II«. .ne Cylinder Age days Number of Horizontal Rows ' Number of Loadings Failure Load kips Average Load kips E I n i t i a l k.s.i. Max. Strain i n / i n 1. 2 E-A-l E-A-2 H 15 6. 6 5 5 20.000 18.450 19.225 6000 irreg. .00230 .00160, 3 E-5-1- 8 5 6 18.800 4080 .00240 A E-5-2 15 5 4 21.660 20.487 3835 .00240 5 E-5-3 15 5 3 21.000 3860 .00215 6 E-4-3* 14 6 4 24.000 8850 .00210 This cylinder was not boiled but cured only by being kept i n the moist closet during 14 days. - to follow page 73 ? 4 and three (Series E-5) had fi v e . The sixth cylinder of table # 17 (E-4-3) was cured only by keeping i t i n the moist closet during fourteen days, i t had six horizontal rows of balls. Cylinders E-4-l and E-4-2 were loaded six times each. They had the following characteristics (See Graph #20): i ) The f i r s t curve started i n both cases with a small irregularity, too small to give a clear indication of i t s cause but which looked lik e the beginning of an upward concavity, from the second one on they started definitely concave upwards, each curve having a larger concavity than the one preceding i t . i i ) The maximum modulus of each reloading curve i s smaller than the maximum of the former one. i i i ) Curves # 2, 3 and 4 had a tendency to continue straight where the former curve had begun flattening. Both cylinders of series E-4 were unloaded when failure was imminent i n the f i f t h loading. The sixth curves were irregular, total failure occurring at a load much smaller than the maximum. Stress-strain curves of cylinders of Series E-5 had the same characteristics although the beginning of the f i r s t curve was clearly an upward concavity, as seen i n graph # 21. The peculiar shape of the las t part of curve 4 of E-5-2 was due to failure occurring while the load maintainer was being adjusted. 75 Cylinder E-4-3 (Graph # 22, line 6, Table # 17) was cured only in the moist closet for fourteen days. It belonged to the same series of E-4-1 and E-4-2 and was tested at the same age. Its results differed in that i t proved considerably stronger and its f i r s t loading curve started straight, while its successive loading curves started concave upwards. Failure: It was apparently caused by buckling of the columns of balls, i t was usually one-sided. The centre core remained in one piece not showing indications of cracking. At failure five or six vertical cracks appeared on the surface of the cylinders on top of the vertical columns of balls, starting at the middle of the specimens but not always coming to the ends. The adhesion between balls and paste was generally good, except when the balls were rusted, i n which case they separated very easily from the paste. Conclusions: The results of these tests on Series E-4 and E-5 indicate that: a) The steam-cured specimens were slightly cracked before the tests. As a consequence their f i r s t stress-strain curves started concave upwards. The specimen which was not steam-cured had the fir s t curve starting straight, hence the i n i t i a l cracking may be a result of steam-curing. b) In specimens under the same conditions those with five rows of balls were stronger than those with six by 7.7$. 76 c) I n the success ive l o a d i n g s the steam-cured c y l i n d e r s had l a r g e r up-wards c o n c a v i t i e s t han i n the f i r s t one, a l s o the m o i s t - c u r e d specimen;;, had curves s t a r t i n g concave upwards i n the succes s ive l o a d i n g s . There-fo re the e x i s t i n g cracks were en la rged and new ones formed w i t h the successeve a p p l i c a t i o n s o f s t r e s s . 10) CEMENT CYLINDERS STEAM-CURED AMD MOIST. WITH STEEL BALL INCLUSIONS  PLACED AS I N PATTERN " I " . S i x c y l i n d e r s o f t h i s type were made and t e s t e d . S e r i e s F - l had seven rows o f s i x b a l l s each and s e r i e s F-2 had s i x . A l l specimens were t e s t e d under a s i n g l e l o a d i n g , t h e i r numer i ca l r e s u l t s are i n t a b l e 18 . These c y l i n d e r s may be d i v i d e d i n two groups, one f o r F - l - 1 , F-2-1 and F-2-3 whose curves began s t r a i g h t , and one f o r F- l-2, F - l-3 and F-2-2 whose curves s t a r t concave upwards. Graphs # 23 and 24 r e s p -e c t i v e l y , are presented as r e p r e s e n t a t i v e o f these groups . I t i s i n t e r e s t i n g to note t h a t two o f the c y l i n d e r s o f t h i s l a s t group had much lower s t reng ths than the o the r specimens o f the same s e r i e s . The upward c o n c a v i t y o f the s t r e s s - s t r a i n curve a t i t s beg inn ing and the lower s t reng ths o f these c y l i n d e r s seem t o i n d i c a t e t h a t they were cracked before the t e s t . As these specimens were not d r i e d , i t i s suspected t h a t c r a c k i n g occur red d u r i n g s t eam-cu r ing . As i n specimens of type 9, the f a i l u r e of these c y l i n d e r s began w i t h v e r t i c a l c racks which appeared on top of the v e r t i c a l l i n e s o f b a l l s . Table 18 CEMENT CYLINDERS STEAM-CURED AND MOIST, WITH STEEL BALL INCLUSIONS PLACED AS IN PATTERN " I " . Ag e Number of Number Failure Average E E Strain Line Cylinder d sHorizontal of Load Load I n i t i a l Max. at Rows Loadings kips kips k . s . i . k.s.iFailure i n / i n 1 F-l-1. 8 7 1 10,970' irreg. 3030 .00180 10.770 2 F-l-2 19 7 1 10.570 C.U. 3540 .00172 3 F-l-3 19 7 1 8.260* C.U. 3380 .00100 A F-2-1 17 6 1. 15.210 5530 5530 .00147 14.525 5 F-2-3 17 6 1 13.840 3790 3790 .00115 6 F-2-2 17 6, 1 11.760* C.U. 3790 .00167 Not considered i n the average C.U. means that the stress-strain curve started concave upwards. - to follow page 76 77 These c y l i n d e r s had twelve v e r t i c a l l i n e s of b a l l s and v e r t i c a l c racks were formed on most o f them. I n most cases the specimens f a i l e d comp-l e t e l y i n one s ide w h i l e the o ther was o n l y c racked . The c e n t r a l cores o f cement always r'emained i n one p i e c e . The moduli of e l a s t i c i t y were sma l l e r i n t h i s type o f c y l i n d e r than i n the type w i t h b a l l s s t and ing on top o f each o the r , and the s t r eng ths were much s m a l l e r . Compared w i t h the average o f s e r i e s E -5 the average s t rengths of these c y l i n d e r s were: S e r i e s F - 2 ( s i x rows of b a l l s ) 11% S e r i e s F - l (seven rows o f b a l l s ) 53.5$ 11) CEMENT CYLINDERS. STEM-CURED AND MOIST. WITH STEEL INCLUSIONS  PLACED AS IN PATTERN " I I I " . The i n c l u s i o n s i n t h i s type of c y l i n d e r were p l aced forming a s i n g l e c e n t r a l column o f b a l l s s t and ing on top o f each o the r . Of the s i x c y l i n d e r s made, th ree had s i x b a l l s ( s e r i e s L - l ) and th ree had f i v e ( s e r i e s L - 2 ) . The numer ica l r e s u l t s of the t e s t s are i n t a b l e 19 . U n f o r t u n a t e l y the f i v e c y l i n d e r s of t h i s type which were t e s t ed under a s i n g l e l o a d i n g were impe r f ec t , they a l l had one b a l l comple te ly out o f l i n e , to the ex ten t t ha t r e a l l y the c e n t r a l column was o f f i v e b a l l s i n s e r i e s L - l and o f four i n s e r i e s L - 2 , consequent ly the gaps o f cement between b a l l s vere r e l a t i v e l y l a r g e ; a l s o the b a l l s were not s t and ing p e r f e c t l y on top of each o ther but were somewhat o f f the Table 19 CEMENT CYLINDERS STEAM-CURED AND MOIST, WITH STEEL BALL INCLUSIONS PLACED AS IN PATTERN "III". . Number of Number Max. Average E E Max. Line Cylinder , g Horizontal of Load Load I n i t i a l Maximum Strain a ^ s Rows Loadings kips kips k.s . i . k . s . i . i n / i n 1. Ir-l-I. 6 6, 1 22.400. 2790 2790 .00470, 22.500 2 L-1--2 6 6 1 22.600 2700 2700 .00400 3 L-l-3 25 6 13 33.750* 3390 3440 .00441 A L-2-1 4 5 1 25.000 274© 2740; .00555 5 L-2-2 4 5 1 24.900 24.233 2650 2650 .00570 6 L-2-3 4 5 1 22.800 2950.. 2950 .00408 * Not considered i n the average. - to follow page 77 78 v e r t i c a l l i n e . The specimens t e s t e d under a s i n g l e l o a d i n g had s t r e s s - s t r a i n curves v e r y s i m i l a r t o the curves f o r neat cement c y l i n d e r s steam-cured and mois t o f comparable age (see graph # 25 and compare i t w i t h graph # 5 o f c y l i n -der c-5-1), but t h e i r u l t i m a t e s t reng ths were somewhat s m a l l e r and the curves were comple te ly f l a t a t f a i l u r e . T h e i r f a i l u r e took the form o f s p l i t t i n g i n two o r three v e r t i c a l c racks (see photograph 2 1 ) . The i m p e r f e c t i o n s i n the p o s i t i o n s o f the i n c l u s i o n s were the s t a r t i n g p o i n t s o f the f a i l u r e c r a c k s , which began where some wedging a c t i o n took p l ace or some t a n g e n t i a l d isp lacement o f the b a l l s o c c u r r e d . C y l i n d e r L - l - 3 (graph # 26) was t e s t e d under repeated l o a d i n g t h i r t e e n t imes , when 25 days o l d . I t s f i r s t curve showed s e v e r a l s i g n i f i c a n t d i f f e r e n c e s from those o f the o the r f i v e specimens t e s t e d , 1. - Much h i g h e r i n i t i a l modulus. 2 . - The curve a t the beg inn ing remained s t r a i g h t f o r about 30% l o n g e r . 3 . - When the curve d e v i a t e d from the s t r a i g h t l i n e i t d e v i a t e d much l e s s and i t s t i l l had a h i g h modulus a t twenty k i p s . Curve 1 had a s m a l l i r r e g u l a r i t y i n the beg inn ing , but i t was v e r y s m a l l and could have been due t o the s t r e s s - s t r a i n r e c o r d e r . to follow page 78 79 Curves 2, 3 and 4 had progressively smaller i n i t i a l moduli, but were also progressively straight for a longer part. Curves 2 and 3 had a larger secant moduli from zero to twenty kips than curve 1, and curve 4 had v i r t u a l l y the same as curve 1. The secant moduli from zero to twenty kips then, decreased steadily from the second curve on. The last part of curve 4 was slightly irregular, and curve 5 started being concave upwards, this concavity increased i n the successive loadings, reaching a maximum i n curve 8. Failure: the failure was sudden and violent, therefore i t was d i f f i c u l t to note where the cracks began forming. There were many radial cracks extending vertic a l l y from end to end, as can be seen i n photographs ,;' 22 and 23. At failure the whole specimen suffered l a t e r a l expansion and i t s ends became tight i n the steel cap. Generali It i s interesting to note the resemblance between graph # 26 of - L-l-3 and graph # 13 of a mortar cylinder steam-cured and moist, of comparable age. The graphs are similar i n that the curves were nearly straight, though L-I-3 had a lower modulus. In both graphs! i ) The f i r s t stress-strain curves were somewhat curved, the subsequent ones got straighter under repeated loadings. i i ) After some loadings the curves began starting concave upwards. Photograph # 22 Photograph # 2 3 to f o l l o w page 79 80. As mentioned above, the c y l i n d e r s o f the same type which were t e s t e d when fou r and s i x days o l d had s t r e s s - s t r a i n curves v e r y s i m i l a r t o neat cement specimens. The d i f f e r e n c e i n modul i and shape o f the curves , and i n g e n e r a l , o f the behaviour o f the specimens o f d i f f e r e n t age g ives p l a c e to. the s u p p o s i t i o n tha t the d i s t r i b u t i o n of s t r e s s e s w i t h i n the specimen may change as the paste hardens. A. cause f o r the d i f f e r e n t behaviour may have been t ha t the i n c l u s i o n s were c o r r e c t l y p l aced i n c y l i n d e r L - l - 3 , but i t s f a i l u r e was; sudden and the re fo re i t was not p o s s i b l e t o observe the p o s i t i o n o f the b a l l s . 12) CEMENT CYLINDERS. STEAM-CURED AND MOIST. WITH STEEL INCLUSIONS AS  I N PATTERN I V . Three c y l i n d e r s of t h i s type were t e s t e d a t ages o f f o u r , s i x and t h i r t y three days . The numer ica l r e s u l t s are t o be found i n t a b l e 20 (see graph 27 ) . The f i r s t i n t e r e s t i n g c h a r a c t e r i s t i c observed i n these specimens i s t h a t the i n i t i a l modul i of e l a s t i c i t y o f the f i r s t l o a d i n g curve were o f the same order for the three c y l i n d e r s . The success ive curves of c y l i n d e r K - l - 3 , which was loaded s i x t imes , presented c h a r a c t e r i s t i c s observed before i n other types o f s p e c i -men as can be seen i n graph 27, b r i e f l y they are:. Table 20) CEMENT CYLINDERS, STEAM-CURED AND MOIST, WITH STEEL BALL INCLUSIONS PLACED AS IN PATTERN "IV". . Number of Number Max. E Max. Line Cylinder , g e Horizontal of Load I n i t i a l Strain days Rows Loadings kips k.s . i . i n / i n K-l-2. A 7 1 15.660. 3280 .00172. E - l - l 6 7 2 18.200 3020 .00240 &.1-3 33 7 6 24.050 3470 .00240 - to follow page 80 81 i ) A tendency to have higher modulus of elasticity than that of the fi r s t curve in the succesive loadings, until a certain limiting load was reached. i i ) The succesive curves continued straight progressively longer. i i i ) Changes in the speed of loading had a definite effect on the stress-strain curves; lower speeds made them flatter, i.e. flattenings at fourteen kips load in curve # 2 and at eighteen kips in curve # 3. The shape of the stress-strain curves of the three cylinders of this type was very different from that of neat cement specimens, and in general i t bears more similarity to the curves of mortar specimens. C) TESTS OF CYLINDERS IN BENDING. RESULTS OBTAINED . In the description of the results and stress-strain curves ob-tained in the twelve different types of cylinders studied, reference has been often made to factors which indicated the formation of cracks in the specimens under compression, previous to their failure. If cracks are formed, only the transverse cracks or those i n c l i -ned at small angles with the axis of the specimens, will be closed by another application of load and make their presence noticeable in the stress-strain curves. The tests of specimens in transverse bending were designed to in-vestigate the transverse cracking. It was already mentioned in section III that two - different set-ups were used. With the equipment available the data 82 obtained consisted of only the ultimate failure loads and the shapes: of failures. Figure 12 shows the set-ups used and the diagrams of the bending moments produced by the loads i n both positions. In every case the failure was sudden. The plane of failure was perpendicular to the axis of the cylinder or very nearly so, i t divided the specimens i n two approximately equal parts. In the f i r s t set-up, there could be some doubt as to whether the failure was produced by bending or by shear, but the position of the failure crack in the centre span in every case where the second set-up was used, proved that failure was due to bending. The fi r s t set-up had the advantage of its simplicity and the disadvantage of a variable bending moment across the length of the specimen. The second set-up should provide a. uniform bending moment over the length of two indies where the stress-strain recorder gauges had measured the axial compression, but with the apparatus available i t was; not possible to control equal loads at both loading points. Results::. A. total of twenty five bending tests were made, nineteen with set-up one and six using set-up two. The results of a l l twenty-five tests are presented in table 21. It can be seen in that table that except for lines 10 and 12 in the tests with set-up one, and lines 22 and 25 in tests with set-up. two, that the bending strength of the various specimens of every type was. uniform, whether or not they had been preloaded. These tests therefore, Table 21 CYLINDERS TESTED IN BENDING Strength T i m e o f Age Preloading i n 0 1 Line Cylinder Composition Curing * ^ Bending f 3 " ^ lbs. f a d i n g 1 C-8-6 Neat Cement S.C.&D. 32 44.00 1880 I 2 C-8-1 Neat Cement S.C.&D. 33 42.75 1855 I 3 C-8-5 Neat Cement S.C.&D. 31 none 1940 I 4 C-10-1 Neat Cement S.C.&M. 8 none 1330 1 5 C-10-5 Neat Cement S.C.&M. 8 none 1050 I 6 C-10-2 Neat Cement S.C.&M. 8 20.40 1300 I 7 C-10-3 Neat Cement S.C.&M. 8 20.00 1250 I 8 C-10-4 Neat Cement S.C.&M. 8 20.00 1260 I 9 C-8-2 Neat Cement M.C.O. 30 none 1516 I 10 C-8-4 Neat Cement M.C.O. 30 37.50 2330 I 11 C-8-3 Neat Cement M.C.O. 30 39.10 1795 I 12 M-2-7 Mortar S.C.&D. 19 none 886 I 13 M-2-3 Mortar S.C.&D. 23 none 1700 I 14 M-2-9 Mortar S.C.&D. 19 27.10 1250. I. 15 M-2-1 Mortar S.C.&D. 23 25.00 1790 I 16 M-3-5 Mortar S.C.&M. 15 none 820 I 17 M-l-2 Mortar S.C.&M. 18 23.60 645 I 18 M-2-2 Mortar S.C.&M. 22 23.00 675 I 19 M-3-2 Mortar S.C.&M. 9 17.88 725 ' I 20, C-ll-3 Neat Cement S.C.&M. 10 22.60 1995 II 21 C-ll-1 Neat Cement S.C.&M. 10 none 1610 II 22 M-2-5 Mortar S.C.&D. 33 none 3560 II 23 M-2-12 Mortar S.C.&M. 30 none 1740 II 24 M-2-26 Mortar S.C.&M. 32 20.60 1567 II 25 M-2-36 Mortar S.C.&M. 14 12.20- 835 II S.C.& D. Means:- Steam-cured and dry. S.C.& M. Means:. Steam-cured and moist. M.C.O. Means: Cured i n the moist closet only. - to follow page 82 83 did not supply the information desired. There were several factors which obscured the results, among them:.-i ) Since the cracking produced i n compression had occurred near the neutral axis of the cylinder i n bending, i t had small influence on the bending strength of the specimen. i i ) . Since incipient cracks produced i n compression were not visible at the surface and not uniform i n the cross section, there was not way to place the failures i n the bending tests i n a position i n which they would affect the results. i i i ) The main defect of this set-up was that the crack, i n order to affect the bending strength, had to be close to the middle, because of the variation of bending moment (see figure 12). D.) CONCLUSIONS. a) General. In this work various properties of cement and mortar which are already known were corroborated, they were:. In specimens of the same composition and age, the dry are con-siderably stronger than the moist. Both i n tension and compression there i s a definite relation between the degree of dryness and the strength of the specimens. 8 4 Neat cement i n compression specimens i s stronger than mortar, both i n wet and dry cylinders. fc). A. factual corroboration of the findings of Dr. Alexander Hrennikoff was obtained. The results indicated the occurrence of cracking i n neat cement specimens when they are dried i n the oven to a constant weight without spec i a l precautions. In waxed specimens the high tension strengths developed by dry briquets and the shape of the s t r e s s - s t r a i n curves of the cylinders tested were good evidence to the e f f e c t that the cracking which i s a consequence of drying can be prevented i f the specimens are properly waxed. c) Factors of importance i n the interpretation of resultst-1. — I t was found that the cement used was of the type which continues hardening after being steam-cured. This i s of considerable importance for future investigations i n t h i s University. There are some Portland cements i n commercial use which, after being steam-cured experience very l i t t l e gain i n strength, but there are others whose strength continues increasing with time ( l , p. 2 3 4 ) . The E l k cement from the B r i t i s h Columbia Cement Company Ltd., belongs to the second group. 2 . — The importance of having the specimens at a constant temperature throughout t h e i r mass and at room temperature when the tests are performed 85 was r e a l i z e d . d) Knowledge ga ined , va luab le f o r f u r t h e r i n v e s t i g a t i o n s :: 1. — An appropr i a t ed way t o c l e a n the i n c l u s i o n s was found i n u s i n g a s o l u t i o n of h y d r o c h l o r i c a c i d . 2 . - The methods used t o p l ace the i n c l u s i o n s i n the specimens gave s a t i s f a c t o r y r e s u l t s and a reasonable degree o f accuracy . 3. - Specimens w i t h i n c l u s i o n s can not be d r i e d wi thou t the occurrence o f c r a c k i n g . C u r i n g i n steam p robab ly causes sepa ra t ions between the i n c l u s i o n s and the cement pas t e , and the re fo re i t i s no t adv i sab le i n i n v e s t i g a t i o n s o f specimens w i t h i n c l u s i o n s . As t h i s f i n d i n g may be extended to mor ta r , i t appears t ha t s team-cur ing may not be an appropr i a t e way to cure mortar specimens f o r l a b o r a t o r y p r a c t i ce . e) End c o n d i t i o n s have a ve ry impor tant e f f e c t on the u l t i m a t e s t r e n g t h o f the c y l i n d e r s and on the shape of t h e i r f a i l u r e . I t i s considered t h a t the conf ined rubber end c o n d i t i o n s used i n t h i s work are an improvement on t e s t i n g w i t h o n l y l u b r i c a t e d ends. f ) The f o l l o w i n g obse rva t ions were ma.de on the r e s u l t s o f the compression t e s t s and t h e i r s t r e s s - s t r a i n curves :.. 1.- The shape o f the s t r e s s - s t r a i n curve i s a f f e c t e d by the speed o f l o a d i n g , t h i s i s a consequence o f creep. I t f o l l o w s t h a t t o o b t a i n comparable r e s u l t s i n a set of c y l i n d e r s i t i s convenient to r u n a l l t e s t s a t the same speed. 86 2.-- The f o l l o w i n g c h a r a c t e r i s t i c s o f the compression curves were genera l f o r a l l t e s t s performed;. i ) I n specimens which were cracked the curves s t a r t e d concave upwards. i i ) When the specimens were subjec ted to l o a d i n g s below a c e r t a i n p o i n t , the i n i t i a l E and l e n g t h o f the s t r a i g h t p a r t o f the curve i nc rea sed w i t h the success ive l o a d i n g s , but when a c e r t a i n l o a d ( d i f f e r e n t i n t he case of each specimen) was passed, the i n i t i a l modul i and s t r a i g h t p a r t s of the curves became p r o g r e s s i v e l y sma l l e r as the number o f l o a d i n g s i n c r e a s e d . i i i ) Mor ta r c y l i n d e r s and specimens w i t h i n c l u s i o n s which were not cracked o r i g i n a l l y , showed i n d i c a t i o n s of t r ansve r se c r a c k i n g i n success ive l o a d i n g s . g) The curves of specimens w i t h i n c l u s i o n s vrere s i m i l a r i n v a r i o u s aspects t o the curves of mortar c y l i n d e r s . Th i s i s considered an impor tan t analogy because one o f the main ob j ec t s i n making specimens w i t h i n c l u s i o n s was t o i m i t a t e the a c t i o n o f the agregate i n concrete and mortar specimens. The ob jec t of i m i t a t i n g a t w i l l the a c t i o n of the aggregate i n mortar and concrete was t o i n v e s t i g a t e the wedging theo ry on the f a i l u r e o f those m a t e r i a l s i n compression, developed by Dr. Alexander H r e n n i k o f f . Th i s work i s to be considered p r e l i m i n a r y t o the s tudy o f the s a i d t h e o r y . 87 h) In specimens i n compression, the presence of cracks previous to their failure was observed and the effects of the transverse cracks were recorded i n the stress-strain curves. The bending tests did not provide a good method for the investigation of the cracks farmed as a consequence of the application of compressive loads, but were very useful i n that they were an aid to realizing the effect of the horizontal cracks i n the stress-strain curves. The failure of specimens with inclusions and the shapes of failure obtained i n the other specimens, indicate that vertical cracks are a more important factor i n failure than the horizontal ones; there-fore an investigation of the vertical cracks by tests i n bending i s l i k e l y to yield more interesting results. This investigation can be made i f cubical test specimens are used instead of cylinders. 88 BIBLIOGRAPHY BOOKS The Chemistry of Cement and Mortar, F.M. Lea and C.H. Desch, Edward Arnold and Company, London. Concrete Manual. U.S. Bureau of Reclamation, U.S., Government Printing Office, 1951. The Design of Reinforced Concrete Structures, Dean Peabody, Jr., John Wiley and Sons, Inc. Engineering Materials. Joseph Marin, Prentice-Hall, Inc., N.Y., 1952. Selected A.S.T.M. Standards for Students in Engineering. American Society for Testing Materials. Strength of Materials, S. Timoshenko, Vol. I and Vol. II, D. Van Nostrand and Co., Inc. TECHNICAL PAPERS Effects of End Condition of Cylinder in Compression. Tests of  Concrete, H.F.. Gonnermann, Proceedings A.S.T.M., Vol. 24, part 2, 1924. The Effects of Aggregate and Other Variables on the Elastic Properties of Concrete. P.M. Noble, Proceedings A.S.T.M., Vol. 31, part 1, p. 399, 1931. The Shearing Strength of Cement Mortar. F.C. Smith and R.Q. Brown, University of Washington, Engineering Experiment Station Bulletin No. 106. Stress Conditions for the Failure of Saturated Concrete and Rock. K. Terzaghi, Proceedings A.S.T.M.., Vol. 45, 1945. The Effect of Steam Treatment of Portland Cement Mortars on Their  Resistance to Sulphate Action, T. Thorvaldson and V.A. 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""Oil." 4 -ft T !-S.-4-- -•!••>!-pj U-.t-j-i-j ,• ! jjt-j' j'jj-j-T!'rT-t-|X!~|~rTr:; uiztp: I-L!.,.:: : i . M . 4 , i •: .1 f44 V i -H-4-4 !• ;-!-}• !-j :!..;;i.::;i^ 98:'HL:;_ '.PETERS CO. Washinatoti 2, D. C, Chart No. 1012 • O. S. PETERS CO. •~r • ,. - j.-4.-i-rpTjXTX:"' x F i - x x i -1—j—i—j—;Jr r r X X X f -X X : . r i r - x •• X t X x x i i x X ' 7 " : x i 1 : ' P X * : i C U : R £ ; D ~ DRV . .xxxx-xxixxxmx:;:'. ..L L 4.4—j L X L ' ; - -, '- ~ ' i - I ' - f ' T ! ' x t x • f x-H X-rtTX!-H" .... f_rr,y..._,_ 1-4-i -rrr •f-r4 " - 4 - ; - - - i - 4 - X ~ rriirlTlT . r r " L t X X -rr-4_ X i - i- '- l . J -XUJXL4LXX-4 Xj~tTIl .4-4-X X 4 X ; . 4 4 AJSiE. ,_..^ .7.V,:D A « S X [ X X J..j_.:J-i^j •' ,|, j j. j_; j... .J.. _j. ' H X J i f ' r + f - f f | 4 X 1 ' X X - i - r XX '4 x t x x ^ X b t : : x : i x i 4 ^ 4 4 x X | . X | x X x X X L X t r •iX-iXX 44! 4. :X --4-H-f ; r X X-p. 1 f X X f 4" M * j - H * !• ' 4 I 4 - X H - I H T T - T - * '-!--r .-.>._!_•_ Z - x i X U x x X t X i • L X 1 x l . ; ' :jx;"[::;..ix: x x : x x i x f e x ^ : 4 - - L . . . . . ; - t -X x x x r . C X ' : ' X ' • X X T 2 X X X f X X ' r - ' - ' ^ : ; t i : X ! : . ! H _ J . . l_L4- . L . i i • • . - } . 1 i - X 4- X X r -.u|r-!u-i - J 4-.4- J~F X X X x X X X x x x l u x t X r T v f t i X i J4. t • I 1 * 1 : 1 ";"[ "rti-f X -I-Xi t+-, : . r r X r X ^ X K -44-4 XXXIXJ-_ i 4 _ U - F X -•i-i.J., X X X X T 1 T-T-ci""!"!" 4 ^ 4 - = r f x + ..r....4.4:H.:f4. TT .4-!. x r i x x x t t T r r - r r j r T T T 4 X L X L X I X -4XRX^ -'+^  " X X r t i " X X T 4 l 4 f u x 4 ] - x : x X x x x t x I X L . X : . ; . . .L-- . , . . i 4 ^ x J x r ± :x::QXx X;q43LXr4 - X 4 G - H -:..-X4X~ f ] t R : ;Xxxx i x x t l : r x t i £ i x rr-.'ZF _ - : i i 4 i x b + | : b ^ X X X [ - x 4 • -1- r i 4. " i X X 4 4 : x x x : 4 X X X 4.4' X X p p : . f 4 4 T r: -pi •*» -x-j... r ; _ •;~nTf" 4! • 1. X j - X X i - t X , "XvT'i i'"" •• - •» - • : - ! • —IV 4 _ 4—4- ....... 4 i X X ! 4 i X ; : " 4:0---L4_ x i x r ••^i^x|":hr±x : -4-4-4 b i s O. S. P E T E R S C O . . . g d l h H y i W X t - r r f i - j - 4 - i X r -r X X i X r X x 4 1 4 . X Washirrst6n ;.2, D. C. ', T" 44-J j T ._ j x x i x Chart No. 1012 o: Washington 2, D. C- Chart No. 1012 . S.. PETERS V/asranston 2, O. C. Chart No. 1012 - 4 4 4 j . ; . : r : " : 4 X X X X X 4 X X X ' I : I i I : , ! -+-l-fr I" - I :' T"t-; x x x , x x i-41 j_;_J ... _ L. .. -I :i.4 ,. U.I..-!.-I-l-.i- : i;f-]47j:.r.!.i!rj:: i i !• : 1 I , • i J4.-U:-. j _ : - r . r j . . - J - L J - U . ; . .L.A-1.. - X X - X - •• X -i-^4-4-X t X t X 4- -4 44 X X . ( . . . ; . - L J - r _ p . l X X XXi-, M 4 4 n X X rr ,.)_L.!- . . .a . , .44 .-. , p- r r r | - M - ^ r r i i j ^ q x f X X ;± r x t x 4 X f : 1 1 xxjX ft; ^ x f ^ j i - f x X X j X x x 4 4 : JX i ^ i 4 i X | -. x x . : 4 XLXftf:HXJ- r|'j'••!".{• J:V|T x t: 47 ztir f : f": xc f x x t i . . . . . . . . . . . ±.__|_ . - T T 4 T 4.4-1.4.^4. X f ; x f X x x x t x • L + . R | 4-r^-4-4- , r r j . r _ r r ^ _ . 4. 4 .,,<.:•. ,i4.4.4...L4. 44X ; J -f j;r 4 p-j j f 4 : -A-XX.: ' ii--">~Q^'T^*r~ - i - f -44. 1...-1 , 4 4 • -• • i • f_ _ . j - I - -;4f4-i-+-r4 '4-L444--}-y-;4-;4.-i-r4i -,-ij-r , . . ^ . . . r ; . . - . j - ^ _ j _ r X H - X X T O X 4 . X l g i : .44 4 4 -":~I'~T_ r i x x p . 14-XXXiXX .,.7X'!' 4; 1 44X-X j. ; X ; " . j x ; X ± . i - p i l T E R / * T E X XXJXX...X?'J R&S^sX QPj 4 . 2 L A 0 4 B 4 4 :. j S T E . ' A / A - i:ui R E. D :. • : :A - -".' i*Rps*;J: . 4 -u. .'.- . - , - i '._ !..' ..1 - i X ;.4_4-4-i-L-i.. ' t - > ' • • 1 ' • . r 1 . 1 : ; A < s E x : ^4:pAyKq7q . r j x x ^ X X -~- r-"r-nj-r-Ti-—!-X f h l l j X , 4Xi4i4X---r T T -rrr ! - ! - _ I.. _(_ L r: .4 ..4 j 4. i_f44-|4— L4rtJ±.i;4i+ •!-4:p:n: -H--i_j.4-4_L _ .... 4 - U 4 L i_i_i_JL_ -4-L 4 4 - 4 .4-i - h r r r n -X-J-PXP-44" -4-f 1 1 1 1 - r-n-4-•4.^rr J-44-4-47: - t ; i ; . : ; ! . : c 4 ± f : --)- -.Uj-i-i-'-.i. 4 . v-44 4-iLL-i + J _ ; . - J , . . ! - . p.41-ttCTrXi: .... T"i- i 4 Ti' — : T — f i • , -- )—r-;Xt^4i.j444l -f-4^4r4-i-i--.y.rj.'j T;"!~j ;f;4:t-44prXb - r T 444.4 ...,4 44. X-frrLl-H:; 4^ ..444t _t_ ^..;-H-|_|„+.-j_i_ X^uXLJia.L" : - 4 4 JT 4444. , 4-Xri/4eL . . . . , - , . . L - r - i , - ! X i f t X - r X -- - " '4mxjxrxx.rX! tt --r-t - . 4 , . x ; i ' 4 4 • r _ _ r j 4 - l O. S. PETERS CO. •Washington. 2, D. C hart No. 1012 O. : 3 . P E T E R S C O . • . -r-r~r - jr- -! ., ,-; .1'}- W >-;--•• X - , -| . ; 4 - ' -J. j . I-J-J..J..- .1 ;.. . I-i (-.;-. J. -f..j ! . •• ^ i_: .1. ., . - L„.Ai -. ~ i~ .. !_' !. Washington 2, D. C. Chart No. 1012 O. S. PETERS CO. :z. J;:;,* - AGE.: W P R h J f u s i o n 'l2 O. S. PETERS CO.. Washington 2, r mmrn ington 2, p.. C. - Chait No. 1012 O. S. PETERS CO. T " •r :i — i L - R T r X X . T p ; 4^ . -i i — .ill [ C E ^ E A t T r C V L - I M O ; L W ! l X W STEEL;:;:2>^'L-L- TVVNC'li.a^lQ/N P 2 >TTE R , T l x : • :.| ._ " " J T f X l ^ S T E ^ M - ( ^ U R : E D - - t 4 : ^ I d i S T " )n 2, O. C. Chart No. 1012 O. S. PETE-US fco. . WashlnstorrE, l^:;T4;X x ; ^ .x!4 :x ^ . ^ X - - ^ ' j r f f i x TI".jZ-| J ^ i - . I X ^ X - | M"j | |" "|T."} ""j " t ^ T - V ' . r j ~ l l l ' j7X~7:! |~ f * ~rt j ^ j~" f H ' 4 4 4xrx ~ T~j~y ~ j x zi:L&\ X • ;; v ; : f t l 4 i r r f T ' t ^ ^ r ^ z p ^ ^ ^ . . X H x f L i q : : -| X 7 X ^ fi: X ; . i . r . 1 : t x d : : :!: i i n L - : 7 f , x r r j i f t t x L r X x ^ x H f e i ^ - - ^ i f c t f c i | x x i x f i : i - : . " p - . f j 4 f j _ r i ± x L x T X 4 : x X X x i x x X : £ : S 4 j - • * x : f j j x L d x i x ^ x T + f r t r x X i - 1 — ' f 1 74:: :;l:fr4;r7ip —r1 —J :—•—-s—••—4—-r-XXXj T L X . U . . 4_ X rtf. -j - r '-t - X .J U. ! jjrr.4 rtr: -H r .. - 7 x . X X . . [• :-j 1 4 4 • 4 p x i 7 7 i x x . y ; x x ff~^M-l-''t-r-i-'-- -4• F 7 - x ; : x ' o x > : .jt;'. T-I-7- - ; - -X - X i ' t x ' I X • Chart No. 1012 O.'S. PETERS CO. . Washington 2,..D.:c. - ; 4 } ; 5 , Chart No; T • o . s. 

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