PLASTIC SHRINKAGE IN DRY MIX S H O T C R E T E by KEVIN NEIL CAMPBELL B.A.Sc. The University of British Columbia, 1995 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE D E G R E E OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF CIVIL ENGINEERING We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA May 1999 © Kevin Neil Campbell, 1999 ln presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia Vancouver, Canada Da,e ' u ro i_ O 1200 1100 1000 900 800 700 600 500 400 300 200 100 0 Comparison of Crack Areas Brazillian Dry Method Shot+remixed+Cast Shot Figure 3.9 - Comparison of crack area between cast and shot samples produced with the Brazilian dry method. The obvious differences between the degree of plastic shrinkage in the cast and shot samples is due to several factors. Presumably, the shotcreting process creates a much stronger bond between the overlay and substrate. The cast specimens were noted to have localized sections of de-bonded concrete, which likely reduced the amount of plastic shrinkage cracking. The cast mixes had a much higher apparent workability than the shotcrete samples even though both mixes were identical. The compaction caused during the shooting process gives the shotcrete an inherent stiffness. After the sample was re-worked the mixes became much more fluid. This is possibly due to the entrainment of air during the mixing and placing operations. Additional air would have the effect of increasing the apparent workability of the mix. Cast samples had more of a tendency to bleed than shot samples. It is believed that during the re-mixing and placing process bleed channels are formed throughout the fresh sample that would not have formed in the shotcrete sample. The presence of bleed water would reduce the amount of plastic shrinkage cracking. 60 It is interesting to note the crack areas of the cast samples are very similar to the "Over Finished" shotcrete sample. Table 3.8 compares the plastic shrinkage crack data of the "Over Finished" shotcrete sample with the shot-remixed-cast samples. All samples were produced using the Brazilian Method and bone-dry material. The "Over Finished" sample was shot and finished vigorously with a steel trowel. The cast samples were produced by first shooting the mix, re-mixing it and then casting it into the mold. Table 3.8 Comparison of Over Finishing with Cast Samples Mix ID Placement Method Crack Data Total Length (mm) #of Cracks Crack Area (mm2) Max. Width (mm) 6-25 Shot-remixed-cast 990 2 179 0.25 6-24 1270 3 151 0.20 6-21 505 2 144 0.15 5-7 Shot, then finished excessively 775 Multiple 119 0.35 3.6.3.2 Paste Content Although all mixes were batched and shot identically, variation in the amount of rebound can affect the paste content. The paste content is defined as the mass of "cement + water + air" per cubic meter of shotcrete. As no measurement of the air content of the mixes was made, the effect of air was not considered. 61 E Q> o re o Effect of Paste Content on Crack Area Shotcrete Samples 500 600 700 800 Paste Content (kg/m3) 900 + Traditional Damp • Traditional Dry A Brazilian Damp x Brazilian Dry Figure 3.10 - Effect of paste content on crack area. As can be seen in Figure 3.10, the paste content of the mix appears to have some influence on the degree of plastic shrinkage cracking only for the Brazilian Dry method. The degree of plastic shrinkage cracking may be more related to the rebound of the coarse aggregate and the total amount of water in the mix. 62 Chapter 4 - Evaluation of Variables Affecting Plastic Shrinkage 4.1 Summary of Variables The final test program involved the evaluation of five different fiber types and two different admixtures that purported to have shrinkage reducing capabilities. The fiber types included three steel types and two different lengths of a straight Polyolefin fiber. The admixtures included a drying shrinkage controlling admixture and a waterproofing admixture. Table 4.1 presents a summary of the variables considered for the final test program and the respective mix identification numbers. All mixes, with the exception of 1-15 and 2-12, were shot with the dry-mix process using the Brazilian method and bone dry material. The base shotcrete mix is presented in Table 3.3 in Chapter 3. Fiber dosage listed in Table 4.1 is listed as the as-batched dosage rate. 63 Table 4.1 Summary of Variables in the Final Test Program Mix ID Variable* Batched Dosage Rate** 4-3 Control -5-16 -5-27 Hooked End Fiber 9 kg/m3 12-9 10 kg/m3 6-4 18 kg/m3 10-16 20 kg/m3 5-23 27 kg/m3 10-18 40 kg/m3 10-19 60 kg/m3 12-11 Flattened End Fiber 10 kg/m3 12-13 20 kg/m3 10-7 40 kg/m3 12-3 Crimped Fiber 20 kg/m3 10-24 40 kg/m3 10-25 60 kg/m3 5-28 Straight 50 mm Polyolefin Fiber 1.50% 5-29 3.00% 6-5 Straight 25 mm Polyolefin Fiber 0.25% 6-3 0.50% 5-31 1.00% 12-17 Shrinkage Controlling Admixture 1% 12-14 2% 1-15 Wet Mix Control -12-12 Waterproofing Admixture (Wet Mix) 1.50% * All mixes, with the exception of mixes 1-15 and 12-12, were shot using dry mix shotcrete with the Brazilian method and bone-dry material. ** For steel fibers the value is the mass fraction in kg/m3. For Polyolefin fibers the value is the volume fraction expressed as a percentage. For the admixtures, the value is the batched dosage expressed as a percentage by weight of cement. 4.1.1 - Presentation of Data Fiber contents are listed as both the as-batched and in-situ volumes. In-situ fiber contents are presented as volume fractions and mass fractions and are based on densities of 64 7850 kg/m3 for steel and a density of 910 kg/m3 for Polyolefin. All shotcrete used in this study was shot at an extremely wet consistency. The observed fiber rebound rates were extremely low compared to typical practice. For this reason no fiber rebound values have been listed as they present unrealistically low rebound rates. Dosages of the shrinkage controlling admixture are listed as a percentage by mass of cement in the batched shotcrete. The amount of the admixture in the shotcrete after shooting could not be assessed, but it is assumed that the amount lost would be low. The dosage of the waterproofing admixture listed is a percentage by mass of cement in the batched shotcrete. The amount of the waterproofing admixture in the shotcrete after shooting could not be assessed. However, assuming the admixture was intimately mixed within the paste, the amount of admixture per mass of cement would remain the same before and after shooting. Table 4.2 presents the results of the in-situ material analysis. The in-situ aggregate, cement and water contents were measured using the procedures outlined in Section 3.5.1 and 3.5.2. The water content listed in Table 4.2 does not include the water absorbed by the aggregate, all aggregate is assumed to be in a saturated, surface dry condition. The as-batched dry-mix shotcrete material listed in the first row of Table 4.2 is a theoretical amount and is based on an assumed water/cement ratio of 0.40. The aggregate is assumed to be in a saturated, surface dry condition; water absorption of the aggregate is accounted for in these values. 65 Table 4.2 In-situ Material Content Analysis of Final Test Program Mix ID Variable Variable Dosage In-situ Material Content (kg/m3) Coarse Aggregate Sand Cement Water Fiber w/c As-batched Dry-Mix 377 1132 538 (215) - (0.40) 4-3 Control (Brazilian Dry) - 462 1161 437 191 - 0.44 5-16 - 558 923 512 257 - 0.50 5-27 Hooked End Fiber 9 202 1254 558 245 5.8 0.44 12-9 10 245 1205 564 234 3.0 0.41 6-4 18 354 1255 437 212 13.0 0.49 10-16 20 391 1176 464 204 17.0 0.44 5-23 27 209 1247 577 211 21.2 0.37 10-18 40 466 1166 411 187 23.0 0.45 10-19 60 408 1140 464 198 33.0 0.43 12-11 Flattened End Fiber 10 338 1218 474 219 8.0 0.46 12-13 20 309 1254 474 205 16.5 0.43 10-7 40 337 1207 478 199 32.0 0.42 12-3 Crimped Fiber 20 245 1205 564 234 8.0 0.41 10-24 40 362 1238 435 201 16.0 0.46 10-25 60 356 1242 420 196 38.0 0.47 5-28 50 mm Polyolefin 1.50% 375 1205 475 202 7.8 0.43 5-29 3.00% 317 1277 449 211 12.0 0.47 6-5 25 mm Polyolefin 0.25% 294 1255 502 214 1.2 0.43 6-3 0.50% 356 1230 465 213 2.0 0.46 5-31 1.00% 324 1176 532 227 4.6 0.43 12-17 Shrinkage Controlling 1% 323 1237 488 204 - 0.42 12-14 2% 271 1210 552 219 - 0.40 1-15 Wet Mix Control - 342 1028 485 195 - 0.40 12-12 Waterproofing 1.50% 340 1030 490 198 - 0.40 The difference in the as-batched material content and the in-situ material content reflects the variability of shotcrete, even under laboratory conditions. Differences in the values could include such factors as: • Rebound - Rebound during shooting resulted in a loss of some of the coarse aggregate. 66 • "Nozzle slobber" - the term used for paste dripping from the end of the nozzle discussed in Section 2.3.3.4, would result in a loss of paste during shooting. • w/c - The actual w/c ratio listed in Table 4.3 is generally higher than the 0.40 used for the material content calculation of the as-batched dry-mix. • Sampling errors 4.2 - Fiber Analysis The relationship between crack area and fiber volume is clear for all fiber types tested. For an increasing fiber content the amount of cracking is dramatically reduced. Among the fibers tested the Hooked End steel fiber appears to be the most effective fiber at controlling plastic shrinkage cracking. The Flattened End fiber is the second most effective, followed closely by the straight 25 mm Polyolefin fiber. The Crimped fiber, although not marketed as a shotcrete fiber, was used in this study to compare fiber shape efficiency. The straight 50 mm Polyolefin fiber was found to be the most inefficient fiber type tested. It should be noted that all the presented results are for only one particular set of environmental conditions, and although relatively severe, it only represents an evaporation rate of 1.5 kg/m2/hour. More extreme environmental conditions will produce more extensive cracking. The results of this study should not be viewed as an absolute analysis of plastic shrinkage cracking, but more for the trends they exhibit. 67 4.2.1 - Hooked End Steel Fiber The Hooked End fiber was shot at seven different volume fractions. The results of the plastic shrinkage crack analysis are summarized in Table 4.3. Table 4.3 - Summary of Plastic Shrinkage Crack Analysis of the Hooked End Fiber Mix ID Fiber Type Batched Fiber Dosage (kg/m3) In-situ Fiber Mass (kg/m3) In-situ Volume Fraction Plastic Shrinkage Crack Data Total Length (mm) #of Cracks Crack Area (mm2) Max Width (mm) 5-27 Hooked End Fiber 9 5.5 0.07% 1525 6 453 1.10 12-9 10 7.9 0.10% 1280 4 406 1.00 6-4 18 13.3 0.17% 905 6 130 0.50 10-16 20 17.3 0.22% 260 4 75 0.25 5-23 27 21.2 0.27% 240 2 30 0.15 10-18 40 9.4 0.12% 920 3 260 0.70 10-19 60 33.0 0.42% 230 2 11.5 0.05 Figure 4.1 illustrates the relationship between crack area and fiber volume. The fiber volume shown is the as batched volume and does not take into account fiber rebound. It is clear from Figure 4.1, that even a small addition of fibers drastically reduces the amount of plastic shrinkage cracking. 68 Hooked End Fiber Crack Area Vs Fiber Volume 1400 0.00% 0.50% 1.00% 1.50% Fiber Volume Figure 4.1 - Hooked End Fiber; crack area vs. fiber volume. 4.2.2 - Flattened End Steel Fiber The Flattened End fiber was shot at three different volume fractions. The results of the plastic shrinkage crack analysis are summarized in Table 4.4. Table 4.4 - Summary of Plastic Shrinkage Crack Analysis of the Flattened End Fiber Mix ID Fiber Type Batched Fiber Dosage (kg/m3) In-situ Fiber Mass (kg/m3) In-situ Volume Fraction Plastic Shrinkage Crack Data Total Length (mm) #of Cracks Crack Area (mm2) Max Width (mm) 12-11 Flattened End 10 7.9 0.10% 1120 3 411 1.15 12-13 20 16.5 0.21% 850 2 205 0.50 10-7 40 32.2 0.41% 685 2 118 0.25 69 Figure 4.2 illustrates the relationship between crack area and fiber volume. Flattened End Crack Area Vs Fiber Volume 1E E 1400 - j -1200 l\ 1000 - \ 800 J \ o 03 < 600 -400 -200 -• • 0 -I— 0.00% 0.50% 1.00% 1.50% Fiber Volume Figure 4.2 - Flattened End Fiber; crack area vs. fiber volume. 4.2.3 - Crimped Steel Fiber with Crescent Section The Crimped fiber was shot at three different volume fractions. The Crimped fiber is not the ideal shotcrete fiber; it has a larger ratio of surface area to volume than the other fibers tested and its shape does not appear to be as aerodynamic as the other fibers tested, which may have resulted in a large rebound factor. Furthermore, it is a heavy fiber, reducing its in-situ fiber count. The results of the plastic shrinkage crack analysis are presented in Table 4.5. 70 Table 4.5 - Results of Plastic Shrinkage Crack Analysis of the Crimped Fiber Mix ID Fiber Type Batched Fiber Dosage (kg/m3) In-situ Fiber Mass (kg/m3) In-situ Volume Fraction Plastic Shrinkage Crack Data Total Length (mm) #of Cracks Crack Area (mm2) Max. Width (mm) 12-3 Crimped Fiber 20 11.0 0.14% 1755 5 574 1.00 10-24 40 15.7 0.20% 1360 4 391 0.80 10-25 60 37.7 0.48% 380 2 135 0.35 Figure 4.3 illustrates the relationship between crack area and fiber volume. Crimped Fiber with Crescent Section Crack Area Vs Fiber Volume CO CD o CD i— O 0.00% 0.50% 1.00% Fiber Volume 1.50% Figure 4.3 - Crimped Fiber; crack area vs. fiber volume. 71 4.2.4 - Straight 25 mm Polyolefin Fiber The Straight 25 mm Polyolefin fiber was shot at three different volume fractions. The fiber measures 25 mm in length and 0.38 mm in width. The fibers are supplied in taped bundles that measure 75 mm in diameter. The fiber bundles are referred to as "pucks" because of the resemblance to a hockey puck. Although shot using the dry-mix process in this study, it is not recommended for use in dry-mix generally. The shotcrete produced in this study had a high cement content and was shot at a very wet consistency. Shotcrete applied in most situations would have a lower cement content and would be shot at a much drier consistency. This would have increased the rebound factor dramatically. Synthetic fibers, being of a much lower density than the shotcrete materials, tend to "fly away" during the shooting process. The use of synthetic fibers in wet-mix is common and does not suffer from the detrimental effects of large rebound. The Polyolefin fibers finished with greater ease when compared to the steel fibers and were relatively easy to dispense into the mix when added at dosages below 4 kg/m3 (0.44% by volume). The results of the plastic shrinkage crack analysis are presented in Table 4.6. 72 Table 4.6 - Results of Plastic Shrinkage Crack Analysis of the 25 mm Polyolefin Fiber Mix ID Fiber Type Batched Fiber Dosage In-situ Volume Fraction Plastic Shrinkage Crack Data Total Length (mm) #of Cracks Crack Area (mm2) Max Width (mm) 6-5 25 mm Polyolefin 0.25% 0.13% 1550 5 502 0.85 6-3 0.50% 0.22% 780 4 207 0.95 5-31 1.00% 0.51% 700 3 72 0.30 igure 4.4 illustrates the relationship between crack area and fiber volume for the 25 mm Polyolefin fiber. 25 mm Polyolefin Fiber Crack Area Vs Fiber Volume 1= ro o ro L-o 1400 0.00% 0.50% 1.00% Fiber Volume 1.50% Figure 4.4 - Straight 25 mm Polyolefin Fiber; crack area vs. fiber volume. 73 4.2.5 - Straight 50 mm Polyolefin Fiber The Straight 50 mm Polyolefin fiber was shot at two different volume fractions. The Straight 50 mm Polyolefin fiber is similar to the Straight 25 mm Polyolefin fiber, but measures 50 mm in length and 0.63 mm in diameter. This fiber was originally chosen because its mass was similar to that of a single Hooked End fiber. Its use would illustrate the effects of fiber density within the shotcrete matrix. Although this fiber is 50 mm in length it was shot through a 50 mm diameter hose. The pump was quickly plugged during this process. Table 4.7 summarizes the results of the plastic shrinkage test data. Table 4.7 - Results of Plastic Shrinkage Crack Analysis of the 50 mm Polyolefin Fiber Mix ID Fiber Type Batched Fiber Dosage In-situ Volume Fraction Plastic Shrinkage Crack Data Total Length (mm) #of Cracks Crack Area (mm2) Max. Width (mm) 5-28 50 mm Polyolefin 1.50% 0.86% 615 3 95 0.30 5-29 3.00% 1.32% 155 1 16 0.20 Figure 4.5 illustrates the relationship between the crack area and in-situ fiber volume of the straight 50 mm Polyolefin fiber. 74 50 mm Polyolefin Fiber Crack Area Vs Fiber Volume 1400 -. , c < 600 -o 400 - X . CD 6 200 -o] . 4 -; * J 0.00% 0.50% 1.00% 1.50% Fiber Volume Figure 4.5 - Straight 50 mm Polyolefin Fiber; crack area vs. fiber volume. 4.2.6 - Comparison of Fibers To compare different fiber types the crack area versus fiber volume is illustrated in Figure 75 Comparison of Fibers Crack Area Vs Fiber Volume in in 0.00% 0.20% 0.40% 0.60% 0.80% 1.00% 1.20% 1.40% 1.60% Fiber Volume Figure 4.6 - Comparison of Fibers; crack area vs. fiber volume. As seen in Figure 4.6 there appears to be a clear difference in fiber performance. For a given fiber volume the Hooked End fiber outperforms other fibers significantly. A comparison of fiber performance based on mass fraction, instead of volume fraction results in some drastic differences. Steel fibers, at a density of 7850 kg/m3, are far out-performed on a per mass basis when compared to synthetic fibers at a density of 910 kg/m3. As is clear in Figure 4.7. the polyolefin fibers have a much improved efficiency when compared to the steel fibers on a fiber mass basis. The fiber mass listed is based on in-situ fiber volume fraction and already accounts for rebound. E E, ra o n u O 50 mm Ftilyolef . . . . Crimped 25 mm Fblyolef . _ Flattened End _ _ _ _ _ Hooked End 76 Comparison of Fibers Crack Area Vs Fiber Mass 1400 , 0 5 10 15 20 25 30 35 40 45 50 55 60 Fiber Mass (kg) Figure 4.7 - Comparison of Fibers; crack area vs. In-situ mass fraction. Max Crack Width vs Fiber Volume 50 mm Polyolefin . . Crimped . . Rattened Bid Hooked End 25 mm RDlyolefin Fiber Volume Figure 4.8 - Comparison of Fibers; maximum crack width vs. In-situ volume fraction. 77 The correlation of maximum crack width with fiber volume is clear in Figure 4.8, but not as well defined as the relationship between total crack area and fiber volume. Reasons for this may in part be due to the more subjective measurement of a single crack width. The maximum crack width defines the slab by one measurement; the crack area value is composed of the sum of numerous cracks' length times their width. The larger number of measurements necessary to obtain the crack area value averages the results. A single poor measurement would not skew the results drastically in the determination of the crack area as could happen with the maximum crack width. It can be seen that the use of even a very small amount of fibers will drastically reduce crack widths. 4.2.6.1 Fiber Geometry The effect of fiber geometry on plastic shrinkage cracking was examined by comparing the crack area with the number of fibers present within the mix. 78 Crack Area Vs Number of Fibers 0.00 500,000.00 1,000,000.00 1,500,000.00 2,000,000.00 Number of Fibers Figure 4.9 - Comparison of Fibers; crack area vs. number of fibers. A small sample of each fiber type was counted and recorded. The corresponding number of fibers per unit mass is shown in Table 4.8. The crimped fiber, with a much smaller length/diameter (l/d) value, has a much smaller fiber count than the Hooked End and Flattened End fibers with equivalent lengths. The 25 mm Polyolefin fiber, with a higher l/d ratio and a density less than 8 times that of steel, has a very high fiber count when compared to the other fibers. The 50 mm Polyolefin fiber, with its long length and large diameter has a fiber count comparable to the steel fibers. 79 Table 4.8 - Unit Quantity of Fibers. Fiber Type # of fibers per 1.000 kg Hooked End 22 400 Flattened End 10 500 Crimped 6 800 25 mm Polyolefin 364 000 50 mm Polyolefin 40 400 For the steel fibers evaluated the number of fibers within the matrix is the controlling factor. It is clear in Figure 4.9 that when the number of fibers contained within each mix are compared, very little difference is evident between the differing steel fiber types. This observation may indicate that fiber shape is not a factor in plastic shrinkage cracking and that the mass per surface area of fiber is the most important factor. However, as no straight, undeformed steel fibers were evaluated, Figure 4.9 may indicate that only a minimum degree of deformation is required to achieve enough bond to control cracking in the plastic state. All of the steel fibers had some degree of deformation. The stresses and strains produced by plastic shrinkage in plastic shotcrete are very low. As stresses within the fiber are very low, fiber strength is not a factor, however the effect of fiber stiffness may be a factor. Balaguru (1994) found that a lower modulus of elasticity in the fiber provided better crack control than fibers with a higher modulus. The beneficial effect of the lower modulus in the Polyolefin fibers is not readily apparent in Figure 4.9. The 25 mm Polyolefin fiber performed very poorly compared to the other fibers in terms of fiber count. 80 The 50 mm Polyolefin fibers' performance is comparable to the steel fibers. An explanation of the relatively poor performance of the 25 mm Polyolefin fiber may be its shape. The relatively poor performance of the straight 25 mm Polyolefin fiber on a per fiber basis may suggest that some degree of fiber deformation may be required for fibers to perform efficiently as crack control even in plastic shrinkage. Much research has been carried out on the effect of fiber shape on flexural and tensile strength of concrete. It is generally agreed that fiber shape has a large effect on crack control in concrete. Kovler et al (1992) found that a rougher surface texture on the fibers was found to reduce cracking in drying shrinkage tests. This would suggest that fiber shape is an important factor in drying shrinkage crack resistance and possibly in plastic shrinkage. Reasons for the relatively good performance of the 50 mm Polyolefin fiber are puzzling. The 50 mm Polyolefin fiber may have had enough length to provide sufficient bond to offset its lack of shape, this fiber was almost twice as long as all other fibers evaluated. The lower modulus of elasticity in the Polyolefin fibers may have somewhat offset there lack of deformation. 4.2.6.2 Fiber Rebound To incorporate the effects of fiber rebound into the plastic shrinkage resistance; Figure 4.10 shows the relationship between the crack area and the as-batched fiber mass. The as-batched fiber volume is the volume fraction of fibers added to the mix prior to the shooting process. 81 Fiber Efficiency Crack Area Vs Batched Fiber Volume - r 1 1 ~ —T 0.00% 1.00% 2.00% 3.00% Batched Fiber Volume Figure 4.10. - Fiber Efficiency; crack area vs. batched fiber volume. The relatively poor efficiency of the Crimped fiber is attributed partially to its high rebound factor. 4.2.6.3 Optimum Fiber Design for Plastic Shrinkage Control Considering the results of this study, the optimum fiber for control of plastic shrinkage cracking in shotcrete would have the following criteria: Fiber for Dry-Mix Shotcrete • A high l/d ratio with minimum length of the size of the coarse aggregate • Steel • Some form of deformation on the fiber 82 A steel fiber is recommended for dry-mix shotcrete to minimize fiber rebound. Fiber for Wet-Mix Shotcrete • A high l/d ratio with a minimum length of the size of the coarse aggregate • Low modulus of elasticity • Some form of deformation on the fiber Some form of Poly fiber is recommended for wet-mix shotcrete where fiber rebound is not as much of an issue, compared to dry-mix. 4.3 Shrinkage Controlling Admixture A shrinkage controlling admixture meant to reduce long term drying shrinkage was evaluated. The admixture is packaged in a liquid form, making it somewhat more conducive for use in wet-mix shotcrete. The admixture was used in this study in dry-mix shotcrete for comparative purposes. The shrinkage controlling admixture is alcohol based, having a specific gravity of about 0.95. To dose the admixture into dry-mix shotcrete it was added into the water line of the nozzle during shooting. Knowing the rate of water addition to the dry-mix shotcrete through the pump, a proportioned amount of the admixture was added to the mixing water. Due to the low specific gravity of the admixture, constant mixing was necessary to avoid separation. The shrinkage controlling admixture provided cohesiveness to the mix during shooting, aiding in the ability of the shotcrete to be built-up. As the mix was more plastic, the panels were easier to finish than a conventional shotcrete. 83 A major concern regarding the use of this admixture is the presence of alcohol. During shooting, there was a strong odor of alcohol in the air. Through the shooting process, the fine spray of the material out of the nozzle, promoted the evaporation of the volatile component of the admixture. There would be risks in using this admixture in confined spaces, from combustion and health hazards. The shrinkage controlling admixture was used at two dosage factors, 1% and 2% by mass of cement. The admixture was found to substantially reduce the degree of plastic shrinkage cracking in the samples, see Figure 4.11. The results of the plastic shrinkage crack analysis are presented in Table 4.9. Table 4.9 - Results of Plastic Shrinkage Crack Analysis of the Shrinkage Controlling Admixture Mix ID Admixture Batched Admixture Dosage Plastic Shrinkage Crack Data Total Length (mm) #of Cracks Crack Area (mm2) Max Width (mm) 12-17 Shrinkage Controlling 1% 975 3 276 0.7 12-14 2% 755 3 91 0.3 84 Shrinkage Controlling Admixture Crack Area Vs Admixture Dosage _ 1400 -r-*!= 1200 ^ E. 1000 -S 8 0 0 -< 600 -•g 400 -w -i 1 1 j 1 0.00% 0.50% 1.00% 1.50% 2.00% Admixture Dosage Figure 4.11 - Shrinkage Controlling Admixture; crack area vs. admixture dosage. 4.4 Wet-Mix Study Wet-mix shotcrete was used briefly in this study for the evaluation of an admixture that could only be used in wet-mix shotcrete. The wet-mix shotcrete was the same material used in the bulk of this study. The same material was batched as the dry-mix, but with the exception that water was added prior to adding the material to the pump. The plastic shrinkage cracking characteristics of the plain wet-mix shotcrete were similar to the pre-dampened dry-mix shotcrete results. 85 4.4.1 Waterproofing Admixture A cementitious based waterproofing admixture was evaluated for its benefits of controlling plastic shrinkage. The manufacturer also purports that the admixture "Inhibits shrinkage and cracking" in concrete. The admixture is typically used in wet-mix shotcrete. 4.4.2 Results of Waterproofing Admixture Study The admixture appears to act as a water reducer and also entrains a small amount of air, thus increasing the workability of fresh concrete. The mix was pumped and shot easily due to the increased workability. Finishing the mix was also easier due to the "fattiness" of shotcrete produced by the increased air content. The waterproofing admixture was added to a wet-mix shotcrete at a dosage rate of 1.5% by mass of cement. The results of the plastic properties, hardened analysis and crack analysis are presented in detail in Appendix A. The admixture was found to have no significant effect on the reduction of plastic shrinkage cracking in wet-mix shotcrete. The results of the plastic shrinkage crack analysis are summarized in Table 4.10. The effects of this admixture on drying shrinkage were not evaluated in this study. Table 4.10 - Results of Plastic Shrinkage Crack Analysis of the Waterproofing Admixture Mix ID Variable Batched Dosage Plastic Shrinkage Crack Data Total Length (mm) # of Cracks Crack Area (mm2) Max Width (mm) 1-15 Wet Mix Control - 727 4 927 1.2 12-12 Waterproofing Admixture 1.50% 645 5 1013 1.3 86 4.5 General Discussion of Test Program Plastic shrinkage cracks observed in this study generally formed within two to five hours after shooting, this time of three hours would be considered the plastic crack window discussed in Chapter two. The widest cracks generally are the first to appear. As is clear in Figure 4.12, the longer the delay to the initiation of cracking the smaller the size of cracks that would form. E *•> U ro o "ro 1.2 1 0.8 0.6 0.4 0.2 0 0 Time of Crack Appearance All Data 60 4»N • • • 120 180 Time (minutes) 240 300 Figure 4.12 - Time vs. final crack width. The presence of fibers was found to delay on the onset of cracking. It is likely that the fibers improve the plastic strength of the shotcrete just enough to reduce both the duration of the plastic crack window and increase the differential between the strength of the shotcrete and the stress exerted by the evaporation. 87 Generally, the wider the crack, the greater the depth it would penetrate. Cracks with a width of greater than 0.5 mm would be full depth of the 50 mm overlay. Cracks with a width of less than 0.5 mm would be categorized surface cracks, extending partial depth into the 50 mm overlay. In shotcrete samples cracks were generally oriented perpendicular to the long direction of the sample. This directional cracking is expected as the majority of the strains is in this direction, but may also be a result of the finishing process. Finishing was always performed parallel to the long direction of the sample. This process may have created sub-surface tears in the stiff shotcrete, promoting cracking. Fiber reinforcement in the overlays obviously reduced crack widths and depths in this study. The fibers reduced crack widths by bridging the crack and providing dimensional restraint. Fibers would not prevent the cracks from forming on a microscopic level, but they prevent them from growing. As the cracks are surface initiated, fibers have the added benefit of preventing cracking from occurring full depth of the overlay. The fibers may have had the added affect of reducing evaporation rates from the overlay by forming a more cohesive matrix. The effect of reducing evaporation rates from the overlay was likely exhibited by the shrinkage controlling admixture. The shrinkage controlling admixture produced a more cohesive mix and may have bound water into the mix more intimately than the plain mixes. The reduction in the loss of water from the mix will prevent plastic shrinkage cracking. The ability of fibers to reduce evaporation may partially explain the lack of differences in plastic shrinkage cracking between differing fiber shapes. 88 Chapter 5 - Conclusion and Recommendations for Future Research 5.1 - Conclusion The proposed test procedure and setup can be used to study plastic shrinkage cracking in bonded shotcrete overlays. In dry-mix mix shotcrete the Brazilian method using bone-dry materials was found to create significantly more plastic shrinkage cracking than other dry-mix mix shotcreting methods. Furthermore, shotcrete samples were found to be more susceptible to plastic shrinkage cracking than samples that were shot, remixed and then cast. The use of fiber reinforcement was found to significantly reduce the amount of plastic shrinkage cracking. Fiber reinforcement reduced both crack widths and the number of cracks appearing. The shrinkage controlling admixture was found to significantly reduce the amount of plastic shrinkage cracking. The waterproofing admixture was found to have no significant effect of the amount of plastic shrinkage cracking. 5.2 - Suggestions and Recommendations for Future Research on the Subject Future research should focus on the fundamentals of plastic shrinkage cracking in shotcrete. Testing should be carried out within an enclosed room to accurately vary environmental conditions. The effect of humidity and temperature should be studied. 89 In the future the concept of crack density may be a better way to compare samples. The crack density would be defined as the Crack Area/Slab Area and expressed in a percentage. This would be useful for comparing specimens of different sizes or to compare lab samples to field situations. The effect of sample size should be studied using full size test panels. The use of full size test panels under real conditions would be ideal. Large panels, 2 or 3 metres square could be covered with a thin layer of shotcrete and allowed to cure for a period of time. The panels would then be covered with a thin shotcrete overlay and allowed to shrink and crack in the field. Testing could be carried out on a hot windy day to maximize cracking. Companion panels, cast at the same time in the field, could be transferred into the lab and placed under identical conditions within the test chamber. A comparative analysis could validate the test setup and procedure. The effect of fiber stiffness and shape should be evaluated. Fibers with similar shape, but different material should be compared to ascertain the effects of modulus of elasticity. Straight and deformed fibers of the same material should be tested to investigate the effect of fiber geometry. The ability of fibers to prevent evaporation from fresh shotcrete should be studied more closely. Restrained shrinkage test samples could be placed on scales within the test chamber to accurately measure evaporation rates during drying. 90 References American Concrete Institute, ACI 506R-90, Guide to Shotcrete, ACI, Detroit, 1990. Sprayed Concrete: Properties, Design and Application (Edited by S.A. Austin and P.J. Robins). McGraw-Hill, New York, 1995. Austrian Concrete Society, Guideline on Shotcrete, Austrian Concrete Society, Vienna, 1990. Balaguru, P., Contribution of Fibers to Crack Reduction of Cement Composites During the Initial and Final Setting Period, ACI Materials Journal, V. 91, No. 3, May-June 1994, pp. 280-288. Banthia, N., Azzabi, M., and Pigeon, M., Restrained Shrinkage Cracking in Fiber-Reinforced Cementitious Composites, RILEM Materials and Structures, 1993, 26, pp. 405-413. Banthia, N., Yan, C , and Mindess, S., Restrained Shrinkage Cracking in Fiber Reinforced Concrete: A Novel Test Technique, Cement and Concrete Research, Vol. 26, No. 1, pp. 9-14,1996. Bloom, R, and Bentur, A, Free and Restrained Shrinkage of Normal and High-Strength Concretes, ACI Materials Journal, Vol. 92, No. 2, March-April 1995, pp. 211-217. Cabrera, J .G. , Cusens, A.R. and Brookes-Wang, Y. Effect of Superplasticizers on the Plastic Shrinkage of Concrete, Magazine of Concrete Research, Vol. 44, No. 160, September 1992, pp. 149-155. Carlson, R.W., and Reading, T.J., Model Study of Shrinkage Cracking in Concrete Building Walls, ACI Structural Journal, July-August 1988, pp. 395-404. Dahl, P.A., Plastic Shrinkage and Cracking Tendency of Mortar and Concrete Containing Fibermesh, Report No. STF65 A85039, SINTEF Div. FCB, Trondheim, Norway, September 1985. Grzybowski, M., Determination of Crack Arresting Properties of Fiber Reinforced Cementitious Composites, Department of Structural Engineering, Royal Institute of Technology, Stockholm, Sweden, June 1989. Grzybowski, M. and Shah, S.P., Shrinkage Cracking of Fiber Reinforced Concrete, ACI Materials Journal, V. 87, No.2, March-April 1990. Khajuria, A, Balaguru, P., Plastic Shrinkage Characteristics of Fibre Reinforced Cement Composites, Fiber Reinforced Cement and Concrete, Edited by R.N. Swamy, RILEM, 1992, pp. 82-90. Kovler, K., Sikuler, J . , Bentur, Free and Restrained Shrinkage of Fiber Reinforced Concrete with Low Polypropylene Fiber Content at Early Age, Fiber Reinforced Cement and Concrete, Edited by R.N. Swamy, RILEM, 1992, pp. 91-101. Kovler, K, Testing System for Determining the Mechanical Behavior of Early Age Concrete Under Restrained and Free Uniaxial Shrinkage, RILEM Materials and Structures, 1994, XX, pp. 324-330. 91 Kovler, K., Sikuler, J . , Bentur, A., Restrained Shrinkage Tests of Fiber-Reinforced Concrete Ring Specimens: Effect of Core Thermal Expansion, RILEM Materials and Structures, 1993, 26, pp. 231-237. Kraai, P.P., A Proposed Test to Determine the Cracking Potential Due to Drying Shrinkage of Concrete, Concrete Construction, September 1985, pp. 775-778. Malhotra, V.M. , Carette, G.G. , and Bilodeau, A., Mechanical Properties and Durability of Polypropylene Fiber Reinforced High-Volume Fly Ash Concrete for Shotcrete Applications, ACI Materials Journal, V. 91, No. 5, September-October 1994, pp. 478-486. Melbye, T, Opsahl, O, and Holtmon, J, Shotcrete for Rock Support. Sprayed Concrete: Properties, Design and Application (Edited by S.A. Austin and P.J. Robins). McGraw-Hill, New York, 1995. Morgan, D.R., McAskill, N, Carette, G.G., and Malhotra, V.M. , Evaluation of Polypropylene Fiber Reinforced High-Volume Fly Ash Shotcrete, ACI Materials Journal, V. 89, No. 2, March-April 1992, pp. 169-177. Opsahl, O.A., Kvam, S.E., Concrete with EE-Steel Fibers, Report No. STF 65 A82036, SINTEF Div. FCB, Trondheim, Norway, June 1982. Paillere, A.M. , Buil, M., and Serrano, J.J., Effect of Fiber Addition on the Autogenous Shrinkage of Silica Fume Concrete, ACI Materials Journal, V. 86, No.2, March-April 1989, pp. 139-144. Pan, X.W., et al., A Study on Restrained Shrinkage Cracking of Fly Ash Cementitious Materials, 1987 Phillajavaara, S.E., Pihlman, E. , Results of Long-Term Deformation Tests of Glass Fiber Reinforced Concrete, Nordforsk-FRC Project 1974-1976, Delrapport O Technical Research Centre of Finland, Otaniemi, 1978. Ravina, D., and Shalon, R., Tensile Stress and Strength of Fresh Mortar Subjected to Evaporation, Proceedings, RILEM International Symposium on Concrete and Reinforced Concretet in Hot Countries, Technion, Israel Institute of Technology, Haifa, 1971, pp. 275-296. Sarigaphuti, M., Shah, S.P., and Vinson, K.D., Shrinkage Cracking and Durability Characteristics of Cellulose Fiber Reinforced Concrete, ACI Materials Journal, V. 90, No. 4, July-August 1993, pp. 309-318. Saucier, F., Detriche, C.H. , and Pigeon, M, Etude de la Deformabilite en Traction d'un Beton de Reparation, RILEM Materials and Structures, 1992, 25, pp. 335-346. Shaeles, C.A., Hover, K.C. , Influence of Mix Proportions and Construction Operations on Plastic Shrinkage Cracking in Thin Slabs, ACI Materials Journal, V. 85, No. 6, November-December 1988, pp. 495-504. Shah, S.P., Sarigaphuti, M., and Karaguler, M.E., Comparison of Shrinkage Cracking Performance of Different Types of Fibers and Wiremesh, Fiber Reinforced Concrete Developments and Innovations, SP-142, ACI, Detroit, 1993, pp.1-18. 92 Appendix A - Summary of Test Data 93 Table A1 - Calibration Summary: In-situ Aggregate, Cement and Water Content Mix Id Nozzle Material State Placement Technique In-Situ Material kg/m 3 w/c C A . Sand Cement Water Paste 8-15 Traditional Damp Shot 474 1062 529 190 719 0.36 8-14 450 1093 517 194 711 0.38 8-13 450 1094 497 213 710 0.43 8-12 Traditional Dry Cast 348 1264 440 189 629 0.43 8-10 316 1294 447 193 640 0.43 8-9 336 1269 482 200 682 0.41 8-8 Traditional Dry Shot 306 1295 458 194 652 0.42 8-7 341 1260 455 199 654 0.44 8-6 328 1273 459 194 653 0.42 7-10 Brazil ian Damp Cast 187 1346 522 200 722 0.38 7-9 413 1177 467 199 666 0.43 7-8 439 1133 498 185 683 0.37 7-4 Brazil ian Damp Shot 432 1198 444 180 624 0.41 7-3 418 1097 542 197 739 0.36 7-2 437 1151 473 194 667 0.41 6-27 443 1157 465 189 654 0.41 6-25 Brazil ian Dry Cast 343 1250 452 220 672 0.49 6-24 351 1229 480 206 686 0.43 6-21 321 1267 468 209 677 0.45 6-20 Brazil ian Dry Shot 379 1247 446 194 640 0.43 6-19 225 1210 548 280 828 0.51 6-18 291 1304 466 204 670 0.44 6-17 215 1294 516 240 756 0.47 5-9 Braz i l ian Dry Unfinished 657 921 454 218 672 0.48 5-7 Over Finished 671 914 438 227 665 0.52 94 Table A2 - Calibration Summary: Hardened Properties Material Placement Compressive Strengths ASTM C642 Mix Id Nozzle State Technique (MPa) Voids Boiled 7d 7d cast 28d 28d cast Volume Absorption 8-15 Traditional Damp Shot 47.6 66.1 11.1% 4.9% 8-14 47.8 65.5 10.5% 4.7% 8-13 41.7 61.2 10.8% 4.8% 8-12 Traditional Dry Cast 37.6 31.5 47.2 41.3 11.3% 5.0% 8-10 38.2 35.2 50.1 46.8 10.8% 4.8% 8-9 43.1 38.8 58.2 53 11.5% 5.2% 8-8 Traditional Dry Shot 42.7 55.9 13.5% 6.2% 8-7 38.7 46 13.9% 6.2% 8-6 40.2 50.8 12.5% 5.7% 7-10 45.9 31.6 49.4 40.7 10.0% 4.5% 7-9 Brazilian Damp Cast 46 42.4 66.4 48.6 10.7% 4.8% 7-8 52.1 48.2 66.3 60.6 9.2% 4.1% 7-4 Brazilian Damp Shot 45.1 57.7 13.4% 6.0% 7-3 46.6 61.8 12.1% 5.5% 7-2 46.4 60.8 12.2% 5.4% 6-27 42.2 55.5 12.4% 5.5% 6-25 Brazilian Dry Cast 46.2 38.3 65.7 59.1 13.4% 6.1% 6-24 51.9 49.7 58.6 64.8 13.4% 6.0% 6-21 47.4 48.4 62.4 62.5 13.7% 6.1% 6-20 Brazilian Dry Shot 49.5 64.3 13.5% 6.1% 6-19 51.8 65.9 11.4% 5.1% 6-18 58.2 70.6 14.0% 6.3% 6-17 57.1 65.9 12.8% 5.8% 5-9 Brazillian Dry Unfinished 56.9 72.4 5-7 Over Finished 55.4 66.5 95 Table A3 - Calibration Summary: Plastic Shrinkage Results Mix Id Nozzle Material State Placement Technique Crac k Data Total Length (mm) Number of Cracks Crack Area (mm2) Max width (mm) 8-15 Traditional Damp Shot 410 3 542 0.45 8-14 405 3 549.3 0.60 8-13 315 4 690.5 0.80 8-12 Traditional Dry Cast 380 2 121.3 0.15 8-10 320 2 167.5 0.35 8-9 440 3 158 0.20 8-8 Traditional Dry Shot 1795 5 752.1 0.80 8-7 1856 7 796.8 0.50 8-6 1825 6 856.4 0.95 7-10 Brazilian Damp Cast 285 2 198.4 0.30 7-9 390 3 150.2 0.15 7-8 370 2 165.5 0.20 7-4 Brazilian Damp Shot 1355 4 510.2 0.60 7-3 1105 5 724.9 0.80 7-2 1195 4 650.1 0.60 6-27 1480 4 475 0.50 6-25 Brazilian Dry Cast 990 2 178.5 0.25 6-24 1270 3 150.8 0.20 6-21 505 2 143.7 0.15 6-20 Brazilian Dry Shot 1665 5 924.5 1.00 6-19 1885 7 1094.3 1.20 6-18 1565 5 915.2 0.80 6-17 1780 6 968.8 1.15 5-9 Brazillian Dry Unfinished 440 2 404 1.00 5-7 Over Finished 775 NA 119 0.35 96 Table A4 - Final Test Progam: In-situ Aggregate, Cement and Water Content Mix ID Fiber Type Batched Dosage In-situ Material Content kg/m3 CA. Sand Cement Water Fiber Paste w/c 4-3 Control - 462 1161 437 191 0 628 0.44 5-16 - 558 923 512 257 769 0.50 5-27 Hooked End 9 202 1254 558 245 5.8 803 0.44 12-9 10 245 1205 564 234 3 798 0.41 6-4 18 354 1255 437 212 13 649 0.49 10-16 20 391 1176 464 204 17 668 0.44 5-23 27 209 1247 577 211 21.2 788 0.37 10-18 40 466 1166 411 187 23 598 0.45 10-19 60 408 1140 464 198 33 662 0.43 12-11 Flattened End 10 338 1218 474 219 8 693 0.46 12-13 20 309 1254 474 205 16.5 679 0.43 10-7 40 337 1207 478 199 32 677 0.42 12-3 Crimped 20 245 1205 564 234 8 798 0.41 10-24 40 362 1238 435 201 16 636 0.46 10-25 60 356 1242 420 196 38 616 0.47 5-28 50 mm Poly 1.50% 375 1205 475 202 7.8 677 0.43 5-29 3.00% 317 1277 449 211 12 660 0.47 6-5 25 mm Poly 0.25% 294 1255 502 214 1.2 716 0.43 6-3 0.50% 356 1230 465 213 2 678 0.46 5-31 1.00% 324 1176 532 227 4.6 759 0.43 Shrinkage Controlling Admixture 12-17 Shrinkage Controlling 1% 323 1237 488 204 ? 692 0.42 12-14 2% 271 1210 552 219 ? 771 0.40 Wet Mix 1-15 Wet Mix Control - 342 1028 485 195 680 0.40 12-12 Waterproofing 1.50% 340 1030 490 198 ? 688 0.40 97 Table A5 - Final Test Program: Hardened Properties Mix ID Fiber Type Batched Dosage (kg/m3) Compressive Strength Voids Volume Boiled Absorption 7 Day (MPa) 28 Day (MPa) 4-3 Control -5-16 - 48.0 65.4 13.0% 5.8% 5-27 Hooked End 9 59.6 69.5 13.5% 6.0% 12-9 10 43.2 57.8 11.5% 5.2% 6-4 18 44.9 50.8 13.0% 5.8% 10-16 20 47.7 65.2 12.0% 5.4% 5-23 27 56.3 69.5 13.3% 5.9% 10-18 40 43.7 55.7 12.6% 5.7% 10-19 60 47.8 65.0 12.6% 5.6% 12-11 Flattened End 10 47.2 61.9 13.4% 5.9% 12-13 20 42.0 54.3 12.4% 5.5% 10-7 40 46.8 64.0 13.9% 6.2% 12-3 Crimped 20 44.8 59.6 11.3% 5.1% 10-24 40 42.8 56.2 14.0% 6.2% 10-25 60 43.7 56.3 12.3% 5.5% 5-28 50 mm Poly 1.50% 47.4 61.2 12.8% 5.7% 5-29 3.00% no 6-5 25 mm Poly 0.25% 42.0 55.3 11.9% 5.3% 6-3 0.50% 49.3 57.2 12.8% 5.7% 5-31 1.00% 46.7 60.6 12.0% 5.4% Shrinkage Controlling Admixture 12-17 Shrinkage Controlling 1% 45.8 61.2 11.4% 5.1% 12-14 2% 43.6 58.7 12.5% 5.6% Wet Mix 1-15 Wet Mix Control - 38.6 52.8 4.9% 10.7% 12-12 Waterproofing 1.50% 42.1 51.0 5.0% 11.5% 98 Table A6 - Final Test Program: Plastic Shrinkage Test Data Mix ID Fiber Type Batched Fiber Dosage (kg/m3) In-situ Fiber Volume Crack Data Total Length (mm) Number of Cracks Crack Area (mm2) Max width (mm) 4-3 Control - 0.00% 2425 8 1320 1.05 5-16 - 0.00% 2235 8 1257 1.10 5-27 Hooked End 9 0.07% 1525 6 453 1.10 12-9 10 0.10% 1280 4 406 1.00 6-4 18 0.17% 905 6 130 0.50 10-16 20 0.22% 260 4 75 0.25 5-23 27 0.27% 240 2 30 0.15 10-18 40 0.12% 920 3 260 0.70 10-19 60 0.42% 230 2 11.5 0.05 12-11 Flattened End 10 0.10% 1120 3 411 1.15 12-13 20 0.21% 850 2 205 0.50 10-7 40 0.41% 685 2 118 0.25 12-3 Crimped 20 0.14% 1755 5 574 1.00 10-24 40 0.20% 1360 4 390.5 0.80 10-25 60 0.48% 380 2 135 0.35 5-28 50 mm Poly 1.50% 0.86% 615 3 95 0.30 5-29 3.00% 1.32% 155 1 16 0.20 6-5 25 mm Poly 0.25% 0.13% 1550 5 502 0.85 6-3 0.50% 0.22% 780 3 207 0.95 5-31 1.00% 0.51% 700 4 72 0.30 Shrinkage Controlling Admixture 12-17 Shrinkage Controlling 1% ? 975 3 276 0.7 12-14 2% ? 755 3 91 0.3 Wet Mix 1-15 Wet Mix Control 0.00% 727 4 927 1.2 12-12 Waterproofing 1.50% 645 5 1013 1.3 99 Appendix B - Photo Log 100 1. Typical repair surface preparation. Loose deteriorated concrete has been chipped away exposing roughened sub-base and reinforcing. The area has been sand-blasted to remove bruised concrete and corrosion products from the reinforcing steel. 2. Aliva 246 dry mix shotcrete pump and operator. Note the air flow meter located on the pump used to regulate airflow and the water pump used to pressurize water for the water ring. 101 3. Sample set-up within the shooting chamber immediately prior to shooting. The test base is present within the formwork in a saturated, surface damp condition. 4. Initial stages of the shooting, note the large amount of stone rebounding from the panel. 102 5. Shotcreting in progress. The shotcrete has a very wet consistency, used to aggravate plastic shrinkage cracking. 6. Test set-up with the shrinkage samples in place. The three construction heaters are in place with the air flow diverter. The air flow diverter is intended to channel the hot air over the sample. 103 7. Measuring crack widths with the optical microscope mounted on the tracks. UBC DEPT OF CIVIL ENG RESTRAINED SHRINKAGE OF SHOTCRETE MIX NO 4-3 JUNE 1996 9. Mix No. 4-3. Duplicate control sample for test series. 105 , | j j i n i i i I | f - M RESTRAINED SHRINKAGE OF SHOTCRETE MIXN01E-9 DEC 1996 11. Mix No. 12-9. Hooked End steel fiber with a batched fiber dosage of 10 kg/m 106 13. Mix No. 10-16. Hooked End steel fiber with a batched fiber dosage of 20 kg/m3. 14. Mix No. 10-18. Hooked End steel fiber with a batched fiber dosage of 40 kg/m3. 107 17. Mix No. 12-13. Flattened End steel fiber with a batched fiber dosage of 20 kg/m UBC DEPT OF CIVIL ENG RESTRAINED SHRINKAGE OF SHOTCRETE MIX NO 5-29 JUNE 1996 20. Mix No. 5-29. Straight 50 mm Polyolefin fiber with a batched fiber dosage of 3.00%. 110 UBC DEPT OF CIVIL ENG RESTRAINED SHRINKAGE OF SHOTCRETE MIX NO 6-3 JUNE 1996 22. Mix No. 6-3. Straight 25 mm Polyolefin fiber with a batched fiber dosage of 0.50%. 111 UBC DEPT OF CIVIL ENG RESTRAINED SHRINKAGE OF SHOTCRETE MIX NO 5-31 JUNE 1996 23. Mix No. 5-31. Straight 25 mm Polyolefin fiber with a batched fiber dosage of 1.00%. 24. Mix No. 5-9. Unfinished shotcrete sample produced with the Brazilian method and bone dry material. 112 25. Mix No. 5-7. Over finished shotcrete sample produced with the Brazilian method and bone dry material. 113 Appendix C Restrained Plastic Shrinkage Test Procedure 114 Proposed Standard Test Method for the Evaluation of Plastic Shrinkage Capacity in Bonded Shotcrete Overlays 1.0 Scope 1.1 This test method covers determination of the plastic shrinkage capacity of bonded shotcrete overlays exposed to severe drying conditions. 1.2 The term plastic shrinkage capacity as used here is defined as the degree of cracking in the plastic shotcrete overlay. 1.3 This test method is intended to produce comparative results for the evaluation of plastic shrinkage in shotcrete. 2.0 Significance and Use 2.1 Measurements of the degree of plastic shrinkage cracking permit assessment of shrinkage controlling admixtures and fibers in bonded shotcrete overlays. This method is particularly useful for comparative evaluation of plastic shrinkage cracking in different shotcrete mixtures. 3.0 Apparatus 3.1 Molds - The molds for casting test specimens shall measure 1000 mm by 1000 mm and 100 mm in depth. The molds shall be constructed of plywood and shall use wood screws for connections. 3.2 Drying Room and Controls - A drying chamber with a suitable viewing area shall be designed for free circulation of air over the sample. Heating will be provided by three construction heaters. Temperature shall be maintained at a constant 115 rate of 55°C. Wind speed over the sample shall be maintained at a velocity of 5 m/s for the duration of the test. The evaporation rate within the test chamber shall be measured at least once per week. 3.2.1 Evaporation Rate - The evaporation rate within the chamber shall be measured by placing a steel tray with a known mass of water within the drying chamber for a period of 15 minutes. Initial and final masses shall be divided by the area of steel tray to give an evaporation rate in kg/m2/hour. 3.3 Micrometer- A micrometer with a magnification rate of at least 20X and a scale capable of measuring to the nearest 0.05 mm shall be used to measure the widths of all cracks. 3.4 Measure Tape - A flexible tape shall be used to measure the length of ail cracks to the nearest 5 mm. 4.0 Sampling 4.1 Sampling for the water content test and cement test shall only be from the center of the panel. 5.0 Preparation of Rigid Base 5.1 Concept - The rigid base is meant to provide dimensional restraint to the shotcrete overlay. The base is intended to closely resemble a typical reinforced concrete structure that has deteriorated and undergone surface treatment in preparation for repair. All rigid bases for a particular series should be constructed at the same time to eliminate the variability of surface roughness. All rigid bases should be moist cured for at least one week. The rigid bases should 116 not be used in the test program until at least an age of six months. At an age of six months the majority of the shrinkage strains within the bases should be relieved. 5.2 Size and shape - The rigid base shall measure 900 mm by 300 mm and 50 mm deep. 5.3 Material - The rigid base shall be constructed of a 35 MPa concrete. The mix shall contain a 60:40, coarse aggregate:sand aggregate ratio. The coarse aggregate content within the mix shall be of a crushed or angular nature; rounded aggregate should not be used. The base may be nominally reinforced with a wire mesh or reinforcing steel. 5.4 Surface Preparation - The surface of the rigid base shall be produced by applying a surface retarderto the sample after placement. Three hours after the concrete has been placed roughen the surface of the sample by scrubbing the surface with a stiff brush and spraying the surface with a hose. Continue scrubbing the surface until the coarse aggregate is exposed and the panel has a uniform roughness. 6.0 Test Specimens 6.1 Size and Shape - The mold for the plastic shrinkage sample shall be rectangular in dimension, 1000 mm by 400 mm and 100 mm deep. 6.2 Number- Only one test sample shall be taken for each mix. 6.3 Molding - When shooting the sample, the bottom corners will be filled first, followed by the lower half of the mold. After sufficient material is built up in the bottom half of the mold, the nozzle shall be brought in close to the formwork to remove any trapped rebound. The form shall be filled in one continuous operation with no stopping during the shooting operation. 117 7.0 Procedure 7.1 Formwork Preparation - Prepare the formwork with hydraulic oil. Hydraulic oil or similar heavy oil should be used to ease in the removal of the formwork. Other wood form release mixtures tend to bond more to the fresh shotcrete disturbing the sample and initiating cracks. 7.2 Formwork Placement - Place the shrinkage mold beside the compressive strength mold; both should lye on a 60° angle to the floor. Keep the panels close together to ensure the same shooting conditions are used for both panels. 7.3 Sample Placement - Place the rigid base within the shrinkage mold allowing it to rest on two spacer blocks. The spacer blocks can be of any rigid inert material, but must be a 50 mm cube. Ensure the base is in a saturated, surface dry condition before placement. If the base is dry, water will be absorbed from the fresh shotcrete and diminish bond capacity. 7.4 Application of the Shotcrete - Air pressure, pump speed and water pressure must be kept constant during the shooting operations. Once the desired consistency of the material is attained by moderating the amount of water input, begin shooting the companion mold and shrinkage sample. A companion mold is always produced with the shrinkage specimen for hardened analysis of the shotcrete. 7.5 Surface Preparation - Immediately after shooting the shrinkage sample excess materials cut away form the sample using the edge of a steel trowel. A wood float is then used to finish and smooth the surface. Finally a steel trowel is lightly passed over the surface to further smooth the surface. Care must be taken to not overly disturb the shotcrete when finishing and moving the sample, as this will 118 affect the results. The steel trowel finish makes for easy crack identification and measurement. 7.6 Transportation of Sample to Chamber - Immediately after finishing, the sample must be moved into the drying chamber. Special care must be taken to not overly vibrate or disturb the sample during movement. 7.7 Test Setup - The panel is placed perpendicular to the airflow, 200 mm form the front of the fans. The side of the sample that was at the bottom during shooting faces the fans. The heating fans are turned on and the Plexiglas cover is closed creating a covered environment. 7.8 Form Removal - O n e hour after shooting the Plexiglas cover is raised and the forms are carefully removed to expose all four sides of the panel. 7.9 Recording of Data - Record and time the appearance of cracking on the slab. After 24 hours the heaters are turned off and the panel is allowed to cool. The length and width of the cracks are recorded to an accuracy of +\- 5 mm and +\-0.05mm. 8.0 Calculation 8.1 Calculate the crack area by multiplying the length of crack by it corresponding width and record to the nearest 10 mm 2. 8.2 Calculate the water/cement ratio for each mix based on the water content results and the cement content results. 8.3 Calculate the mass of cement per m 3 based on the washout test results. 8.4 Calculate the mass of sand and coarse aggregate content per m 3 based on the washout test results. 119 9.0 Report 9.1 A report shall be made for each specimen tested and shall include the following information where applicable: 9.1.1 Identification number for the test sample. 9.1.2 Shotcrete process used, wet or dry. 9.1.3 Type of pump used in producing the shotcrete. 9.1.4 Batched mix design. 9.1.5 As shot mix contents. 9.1.6 Total length of cracks. 9.1.7 Number of cracks appearing. 9.1.8 Maximum crack width. 9.1.9 Total crack area. 120