Applied Science, Faculty of
Civil Engineering, Department of
DSpace
UBCV
Ravi, Madhuvandhi
Master of Applied Science - MASc
University of British Columbia
Recycling waste materials as replacement for natural resources in building products could help in lowering the environmental impact of the construction industry, provided that their application and processing is properly engineered. Wood waste is one of the chief construction wastes in Canada and many other countries worldwide. In this study, a novel bio-composite panel made with recycled wood chips is presented and assessed. The bio-composite binder was a natural hydrated lime with addition of metakaolin. The inclusion of various additives such as sodium hydroxide, recycled wood ash, and magnesium-rich powder recycled from the cutting waste in the production of magnesium oxide boards, was also explored. The effects of different binder compositions and proportions on the microstructure of the binder, its compatibility with the wood chips, and the engineering properties of the final bio-composite product were investigated. Finally, the effect of different curing conditions is considered, including accelerated carbonation by CO₂ incubation. Following ASTM specifications, 3 replicates of 550 x 550 x 70 mm panels for each bio-composite formulation and curing condition were cast. Specimens were cut from the panel to test the mechanical and thermal properties. Extent of carbonation within the panel was analyzed by standard colouring observation after addition of phenolphthalein and compared with control specimens cured without CO₂ incubation. These analyses were supported by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) of the binders and the bio-composite to monitor the various reactions occurring in the binder, including hydraulic and pozzolanic reactions, carbonation and additional reactions. An optimised binder composition of lime and metakaolin was successfully designed based on the strength data obtained on binder pastes. The bio-composite produced by combining wood chips and the optimised binder possessed good mechanical and thermal properties. While it met the minimum requirements of compressive strength and thermal conductivity as specified by ASTM standards, future work will need to focus on improvement of the flexural behavior. It was also found that carbonation curing of specimens helped in rapid strength gain and improvement of the matrix. Further, microstructure analysis of the bio-composite helped identify and characterise the reaction products that enhanced its properties.
BIO-COMPOSITE PANELS FROM RECYCLED WOOD CHIPS FOR SUSTAINABLE BUILDING APPLICATIONS by Madhuvandhi Ravi B.Tech., National Institute of Technology – Tiruchirappalli, 2017 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES (Civil Engineering) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) August 2019 © Madhuvandhi Ravi, 2019 ii The following individuals certify that they have read, and recommend to the Faculty of Graduate and Postdoctoral Studies for acceptance, a thesis/dissertation entitled: Bio-Composite Panels from Recycled Wood Chips for Sustainable Building Applications submitted by Madhuvandhi Ravi in partial fulfillment of the requirements for the degree of Master of Applied Science in Civil Engineering Examining Committee: Cristina Zanotti, Civil Engineering Supervisor Patrick McGrath, Civil Engineering Supervisory Committee Member iii Abstract Recycling waste materials as replacement for natural resources in building products could help in lowering the environmental impact of the construction industry, provided that their application and processing is properly engineered. Wood waste is one of the chief construction wastes in Canada and many other countries worldwide. In this study, a novel bio-composite panel made with recycled wood chips is presented and assessed. The bio-composite binder was a natural hydrated lime with addition of metakaolin. The inclusion of various additives such as sodium hydroxide, recycled wood ash, and magnesium-rich powder recycled from the cutting waste in the production of magnesium oxide boards, was also explored. The effects of different binder compositions and proportions on the microstructure of the binder, its compatibility with the wood chips, and the engineering properties of the final bio-composite product were investigated. Finally, the effect of different curing conditions is considered, including accelerated carbonation by CO2 incubation. Following ASTM specifications, 3 replicates of 550 x 550 x 70 mm panels for each bio-composite formulation and curing condition were cast. Specimens were cut from the panel to test the mechanical and thermal properties. Extent of carbonation within the panel was analyzed by standard colouring observation after addition of phenolphthalein and compared with control specimens cured without CO2 incubation. These analyses were supported by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) of the binders and the bio-composite to monitor the various reactions occurring in the binder, including hydraulic and pozzolanic reactions, carbonation and additional reactions. An optimised binder composition of lime and metakaolin was successfully designed based on the strength data obtained on binder pastes. The bio-composite produced by combining wood chips iv and the optimised binder possessed good mechanical and thermal properties. While it met the minimum requirements of compressive strength and thermal conductivity as specified by ASTM standards, future work will need to focus on improvement of the flexural behavior. It was also found that carbonation curing of specimens helped in rapid strength gain and improvement of the matrix. Further, microstructure analysis of the bio-composite helped identify and characterise the reaction products that enhanced its properties. v Lay Summary The construction industry is one of the biggest producers of solid waste in Canada. This solid waste includes wood products, concrete and masonry. The wood waste from these sources is often incinerated or disposed in landfills. In this research work, attempts have been made to recycle this wood waste to manufacture a product of commercial and environmental importance. This new material with its promising insulation properties can be possibly used as an insulation panel in buildings. Furthermore, this material also absorbs carbon dioxide, a pollutant gas released from industries, to increase in strength. In this thesis, the properties of the novel bio-composite are studied, and its applications are recognised. vi Preface This thesis presents the original, unpublished work carried out by the author, Madhuvandhi Ravi, in collaboration with the company, Calmura Natural Walls under the supervision of Dr. Cristina Zanotti. In this research work, specimens have been produced and tested by the author according to the ASTM standards and experiments were performed under the purview of the Mitacs Accelerate Graduate Internship. vii Table of Contents Abstract ......................................................................................................................................... iii Lay Summary .................................................................................................................................v Preface ........................................................................................................................................... vi Table of Contents ........................................................................................................................ vii List of Tables ................................................................................................................................ xi List of Figures .............................................................................................................................. xii List of Symbols ........................................................................................................................... xiv List of Abbreviations ...................................................................................................................xv Glossary ...................................................................................................................................... xvi Acknowledgements ................................................................................................................... xvii Chapter 1: Introduction ..............................................................................................................19 1.1 Background ................................................................................................................... 19 1.2 Outline of thesis ............................................................................................................ 20 Chapter 2: Literature review ......................................................................................................22 2.1 Environmental performance scenario in Canada .......................................................... 22 2.2 Bio-composites ............................................................................................................. 22 2.2.1 Wood fibers: characteristics and uses ....................................................................... 23 2.2.2 Major challenges in bio-composite production ......................................................... 25 2.2.3 Binders: Composition and properties........................................................................ 26 2.2.4 Bio-composite curing processes ............................................................................... 27 2.2.5 Bio-composite manufacture ...................................................................................... 29 viii 2.2.6 Performance of bio-composites ................................................................................ 29 2.2.6.1 Mechanical performance ................................................................................... 29 2.2.6.2 Thermal performance ........................................................................................ 30 Chapter 3: Materials and Testing ..............................................................................................32 3.1 Bio-composite ingredients ............................................................................................ 32 3.1.1 Binder ........................................................................................................................ 32 3.1.1.1 Lime .................................................................................................................. 32 3.1.1.2 Metakaolin ........................................................................................................ 33 3.1.1.3 Additives ........................................................................................................... 33 3.1.1.4 Alkali activators ................................................................................................ 35 3.1.2 Fibers......................................................................................................................... 36 3.2 Study on binder performance ........................................................................................ 36 3.2.1 Mixture design .......................................................................................................... 36 3.2.2 Casting technique ...................................................................................................... 38 3.2.3 Curing technique ....................................................................................................... 39 3.2.4 Mechanical Testing ................................................................................................... 39 3.2.5 Chemical and microstructure studies ........................................................................ 39 3.3 Study on bio-composite panels ..................................................................................... 41 3.3.1 Manufacturing process .............................................................................................. 41 3.3.1.1 Screening........................................................................................................... 41 3.3.1.2 Mixture design .................................................................................................. 42 3.3.1.3 Mixing and casting ............................................................................................ 44 3.3.2 Curing process .......................................................................................................... 46 ix 3.3.3 Sampling and cutting ................................................................................................ 47 3.3.4 Testing....................................................................................................................... 48 3.3.4.1 Compressive test ............................................................................................... 48 3.3.4.2 Flexural test ....................................................................................................... 49 3.3.4.3 Thermal testing ................................................................................................. 49 3.3.4.4 Microstructure studies ....................................................................................... 51 3.3.4.5 Chemical studies ............................................................................................... 51 Chapter 4: Results and discussion ..............................................................................................52 4.1 Results from binder studies ........................................................................................... 52 4.1.1 Mechanical test results .............................................................................................. 52 4.1.2 Microstructure studies ............................................................................................... 57 4.1.3 X-Ray Diffraction (XRD) Analysis .......................................................................... 60 4.1.4 Chemical analysis ..................................................................................................... 61 4.2 Results on bio-composite panels ................................................................................... 63 4.2.1 Mechanical test results .............................................................................................. 63 4.2.2 Thermal test results ................................................................................................... 69 4.2.3 Chemical/Microstructure studies .............................................................................. 70 4.2.3.1 Scanning Electron Microscopy (SEM) analysis ............................................... 70 4.2.3.2 Energy Dispersive X-Ray Spectroscopy (EDX) Analysis ................................ 73 4.2.3.3 Carbonation test ................................................................................................ 74 Chapter 5: Conclusion and future research ..............................................................................77 5.1 Conclusions ................................................................................................................... 77 5.2 Recommendations for future work ............................................................................... 79 x References .....................................................................................................................................82 xi List of Tables Table 2.1 Thermal conductivity values of common materials ...................................................... 31 Table 3.1 Composition information of Dolomitic lime used in the study .................................... 32 Table 3.2 Composition information of metakaolin used in the study ........................................... 33 Table 3.3 Mix proportions by weight of binder pastes ................................................................. 37 Table 3.4 Mix designation and composition ................................................................................. 43 Table 3.5 Sample mix design for 60L-40MK ............................................................................... 44 Table 3.6 Sample mix design for 60L-40MK-A ........................................................................... 44 xii List of Figures Figure 2.1 Typical loading curves of hempcrete [43] ................................................................... 30 Figure 3.1 XRD results on wood ash ............................................................................................ 34 Figure 3.2 XRD results on magnesium oxide board waste ........................................................... 35 Figure 3.3 Compression test setup for testing binder paste cubes ................................................ 39 Figure 3.4 Sieves used for screening wood chips in this work ..................................................... 42 Figure 3.5 Mould used for producing panels ................................................................................ 46 Figure 3.6 Cast panels stored for drying after curing ................................................................... 46 Figure 3.7 Sampling plan with specimen designation .................................................................. 48 Figure 3.8 a) Compression test setup and b) flexure test setup .................................................... 49 Figure 3.9 Heat flow meter ........................................................................................................... 50 Figure 4.1 Compressive strength of binder paste cubes of different composition subjected to natural carbonation........................................................................................................................ 52 Figure 4.2 Compressive strength of binder cubes of different composition subjected to accelerated carbonation ................................................................................................................. 53 Figure 4.3 Wet regions near the centre of the cube ...................................................................... 54 Figure 4.4 Influence of lime-to-metakaolin ratio on the strength of binder pastes cured in carbonation chamber (a) and laboratory conditions (b) ................................................................ 56 Figure 4.5 SEM images showing regions of unreacted lime and metakaolin in 60L-40MK-A – a) and c) and 40L-60MK-A – b) and d) ............................................................................................ 57 Figure 4.6 SEM images showing carbonate crystals in different compositions ........................... 58 Figure 4.7 SEM images of binder phase of mix 60L-40MK without sodium hydroxide – (a), (c), (e) and 60L-40MK-A with sodium hydroxide – (b), (d), (f) at 56 days ....................................... 59 xiii Figure 4.8 XRD results of binder different mixes ........................................................................ 61 Figure 4.9 Carbonated (white strips) and non-carbonated (pink) parts of NC cubes – a), c) and AC cubes – b), d) .......................................................................................................................... 62 Figure 4.10 Typical loading curves under compression ............................................................... 63 Figure 4.11 Beam specimen before testing (a) and after testing (b) ............................................. 64 Figure 4.12 Typical loading curve under bending ........................................................................ 64 Figure 4.13 Flexural strength of bio-composite specimens with age ........................................... 65 Figure 4.14 Compressive strength of bio-composite specimens with age .................................... 66 Figure 4.15 Summary of mechanical behaviour of bio-composite specimens at 28 days (a) and 56 days (b).......................................................................................................................................... 67 Figure 4.16 Naturally carbonated specimen (disintegrated during cutting process) .................... 68 Figure 4.17 Thermal conductivity value of bio-composite samples at 56 days ............................ 69 Figure 4.18 SEM micrographs of wood fiber (a) and bio-composite samples at 28 days (b to e) 71 Figure 4.19 SEM micrographs of bio-composite samples at 56 days........................................... 72 Figure 4.20 SEM-EDX elemental maps of 60L-40MK mix along with BSE image ................... 74 Figure 4.21 Beam specimens a) well carbonated and b) poorly carbonated ................................ 75 Figure 4.22 Carbonation map showing the size of uncarbonated regions across the panel .......... 76 xiv List of Symbols % : Percentage °C : degree Celsius Al : Aluminium Ca : Calcium Ca(OH)2 : Calcium hydroxide Ca(OH)2MgO : Calcium magnesium hydroxide CaCO3 : Calcium carbonate CaO : Calcium Oxide CO2 : Carbon dioxide kg/m3 : kilogram per cubic meter kPa : kilo Pascal M : Molar MgO : Magnesium oxide MPa : Mega Pascal NaoH : Sodium hydroxide Si : Silicon W/mK : Watt per meter Kelvin λ : Thermal conductivity xv List of Abbreviations AC : Accelerated carbonation ASTM : American Society for Testing and Materials BSE : Backscattered electrons CSH : Calcium silicate hydrate EDX/S : Energy-dispersive X-ray spectroscopy IPCC : Intergovernmental Panel on Climate Change L/MK : Lime-to-metakaolin ratio MK : Metakaolin MOR : Modulus of rupture NC : Natural carbonation OPC : Ordinary Portland Cement ppm : parts per million RH : Relative humidity SEM : Scanning Electron Microscopy XRD : X-Ray Diffraction xvi Glossary Bio-composite : A type of material formed by the reinforcement of a matrix with fibers of natural origin. Carbonation : It is a chemical process by which carbonates, bicarbonates or carbonic acid are produced from reactions involving carbon dioxide. For example: 𝐶𝑎(𝑂𝐻)2 + 𝐶𝑂2 → 𝐶𝑎𝐶𝑂3 + 𝐻2𝑂 Carbon Sequestration : It is the process of removal of atmospheric carbon dioxide and trap it in a long-term storage facility to combat the issue of global warming and climate change. Ligno-cellulosic fibers: It refers to the fibers of plant origin that are predominantly composed of the polymers, cellulose and lignin Sustainability : It is the ability to manage a resource such that the resource apart being abundant at the present is available for future generations too Thermal conductivity : It is the ability of a material to conduct and transfer heat. It is often measured in W/mK. xvii Acknowledgements I express my profound gratitude to my supervisor, Dr. Cristina Zanotti for her invaluable knowledge and indispensable guidance during the entire phase of my research work. I am thankful for her motivation and persistent support that helped me complete this project. I wish to sincerely thank Mr. Monty Chong-Walden and Mr. Peter Renke of Calmura Natural Walls for offering this wonderful opportunity to work with them and learn the intricacies of bio-composites. I am thankful for the technical support and assistance provided by Mr. Harald Schrempp, Mr. Doug Hudniuk, Mr. Sylvain Picard, Mr. John Wong, Mr. Scott Jackson, Mr. Bill Leung and Mr. Simon Lee during my research endeavour. I wish to express my gratitude to the Materials Research Group for the immense support and benevolent advice during my stay. I am also profoundly thankful for the help extended by the undergraduate assistants Yiwei Chen, Sergey Makhov and William Davis in completing my experiments. Special mention about my colleagues, Joanna Suchta, Bardia Kabirifar and Dr. Farhad Pargar, who supported and guided me every step of the way. I am thankful to Mitacs for the partnership with Calmura Natural Walls and the financial assistance to successfully complete this project. I would like to thank my father Ravi, mother Kavitha and sister Samyuktha and friends Sapna, Arun, Ram, and Anjana for their love, unending support, and eternal motivation that enabled me to work towards my master’s thesis. Finally, I am grateful to the Almighty for providing me with the strength and ability to undertake this research work and for guiding me through life. xviii To my parents, sister and friends who stand by me everyday 19 Chapter 1: Introduction 1.1 Background Changing weather patterns and escalating natural hazards are gradually dominating the news every day. Due to the increasing global temperatures, every major industry is being scrutinized based on the carbon footprint it is leaving behind. According to a report by the IPCC (2014), the world is in now in an era of committed climate change [1]. Data from the National Oceanic and Atmospheric Administration shows that the carbon dioxide concentration is an all-time high and exceeds the value of 400 ppm by volume. The construction industry, a globally important sector, is facing significant changes over this increasing concern of climate change and carbon emissions all around the world. Greenhouse gas emissions, pollution, high-energy requirement, high solid waste generation and exploitation of natural resources associated with the construction sector, all are contributing to these changes [2], [3]. Economic and social development equipped with environmental well-being for present as well as future generations should be the focus of development in the construction sector at present. Hence, in recent days there is an augmented interest over sustainable construction practices and eco-friendly building material. New binders, cementitious systems and aggregates of natural origin and from low carbon sources are being explored. Materials associated with low carbon footprint, a sustainable source of origin, no pollution and low-energy consumption are being studied intensively all over the world to build a sustainable world. That is how the idea of bio-composites has begun gaining momentum. Combining nature-born aggregates with a low impact binder like lime, it is possible to build a sustainable and environment-friendly product. In this research work, an attempt has been made to utilise wood with lime-metakaolin binders to build a resilient and green engineered product. 20 Wooden waste is a significant part of the solid waste produced in the construction industry in Canada. This wood waste, instead of ultimately ending up in incinerators and landfills, is collected from construction waste and used furnishings and chipped into smaller pieces to be used in the product. Transforming waste wood into lime-bonded bio-composites is an attractive technology. Besides serving as a way of recycling wood, it also serves as a cost-effective and efficient material with thermal insulation properties. Using carbon dioxide to gain strength through carbonation, these bio-composites also possess the beneficial property of sequestering carbon dioxide into them. These advantageous properties make this bio-composite material an ideal choice for use in building envelopes. In this thesis, this bio-composite is characterised for its performance and its various applications explored. This research work was done in collaboration with a start-up, Calmura Natural Walls. The composition of the bio-composite was adopted based on some of the preliminary research carried out by Calmura and further investigated in this work. 1.2 Outline of thesis The objective of this thesis was to study the mechanical, thermal and chemical properties of a bio-composite manufactured using waste wood pieces and lime-metakaolin pastes. First, an optimum binder composition was chosen by testing and comparing the performance of pastes of different lime-metakaolin ratio. The chosen binder was then integrated with waste wood chips to produce panel specimens which were tested for their mechanical and thermal performance. The microstructure of the composites was also studied extensively through SEM and EDS analyses. The thesis comprises of five chapters as listed below: Chapter 1 Introduction Chapter 2 Literature Review 21 Chapter 3 Methodology Chapter 4 Results and discussion Chapter 5 Conclusion and future work Chapter 1 lays out the background for the research work. It also embodies an outline of the thesis with short discussion on each chapter. Chapter 2 provides a review of literature work on the overview of construction industry in Canada, types of natural fibers, natural binders, bio-composite manufacture, curing processes and testing methodologies. Chapter 3 covers the methodology adopted in the research work and the details about the materials required. It also includes the details on the mixture design and proportions. Chapter 4 presents the results of mechanical test on binders. It also includes the results on the mechanical, thermal and chemical testing of the bio-composite specimens. Chapter 5 summarises the conclusions of the thesis and offers recommendations for future work. 22 Chapter 2: Literature review 2.1 Environmental performance scenario in Canada The construction industry is one of the highest waste generators in the world with a contribution as high as 20-30% of municipal wastes [4]. In Canada itself, the construction and demolition (C&D) waste make up to 27% of the total municipal solid waste. Out of this lot, wood waste forms a major part of C&D waste in many cities in Canada (up to 22% of wastes from residents and businesses in Vancouver area) according to DLC Waste Management Toolkit of Metro Vancouver [5]. With such significant contributions coming from the construction industry, there is a need to regulate the waste generation and recycling processes. Some of the main ways by which wood waste is disposed are incineration and landfilling. However, with the rising levels of carbon dioxide in the environment and increasing temperatures, several studies are trying to explore the recycling of this waste with methods that leave a lower carbon footprint. One such method is incorporating these wood wastes with a binding component and manufacturing bio-composites. This increases the life of these materials as viable materials instead of being incinerated or disposed off in landfills. 2.2 Bio-composites Bio-composites are manufactured by enclosing natural fibers in a binding matrix. Natural fibers can vary based on their chemical composition. Predominantly these fibers are made of cellulose, hemicellulose, and lignin [6]. Some of the commonly used fibers are jute, flax, hemp, cotton, coir and bamboo. They come from different parts of plants like leaf, stalk, bast or seed. Numerous studies have explored the use of plant fibers or aggregates to make building components. Magniont et al. [7] in their work experimented on hemp shiv and sunflower pith combined with a pozzolanic 23 matrix. They studied the longitudinal and lateral cross- sections of both the aggregates and found that they had a highly porous structure with hemp having tubular porosity and sunflower pith having an alveolar structure. Both these porosities gave the fibers high water absorption characteristic and the potential to be used as bulk insulating materials. In another research work, Dai et al. [8] developed a bio-composite combining wood sawdust and gypsum. They treated sawdust with epoxy and mixed with gypsum and water to produce a bio-composite specimen. The epoxy treatment reduced the water absorption potential of sawdust and helped in improving the mechanical performance of the composite. Aigbomian et al. [9], [10] did numerous experiments on developing building components using sawdust and waste paper. They combined saw dust from waste wood, waste paper and a commercially available lime mixture called Tradical. The mechanical and thermal performance of the resulting wood-crete were appreciable and the potential of the wood-crete to be used as a building material was established. Zhou et al. [11] manufactured a thermal insulation product using cotton stalk fibers without using binder material. The product was built without any chemical additives and resins by just hot-pressing the cotton stalk fibers under exposure to high-frequency heating. The mechanical performance of the board increased with increase in the moisture content during the pressing process. Numerous other studies have been performed by combining lightweight cellulosic plant derived aggregates and with a binding or pozzolanic materials [12]–[14]. 2.2.1 Wood fibers: characteristics and uses Wood fibers can come from a hardwood or a softwood tree. Hardwood trees comprise of monocot species like oak, maple, and walnut and softwood trees comprise of gymnosperm species like pine, cedar, and spruce. Wood fibers/pieces are increasingly considered for use as reinforcing elements 24 in a variety of industries like automotive, building and packaging. Agoudjil et al. [15] in their work on date palm fibers, did a study on their thermophysical, chemical and dielectric properties. They studied the longitudinal and lateral cross-section of the palm fibers under SEM and found that the structure was generally porous. A lignin layer on the surface of the fibers was found to be detrimental in the mechanical performance of the bio-composite. The thermal conductivity of these fibers was found to be close to those of other commercially available wood-fiber insulation boards made of materials like cork, hemp or banana plant fibers. Karmarkar et al. [16] in another study explored the use of eucalyptus fibers as reinforcing component in a polypropylene matrix. They found that the mechanical performance of the composite found through tensile, impact and flexural tests was appreciable and better than its non-reinforced counterpart. Another growing industry for these natural fibers is automotive industry. In order to make auto-parts biodegradable or recyclable, researchers in automotive industries are exploring the application of wood fibers to reinforce polymer matrices [17]. In one such initiative, M. Stark et al. [18] examined the effects of wood fiber on the mechanical performance of wood-polypropylene composites. The stress transfer characteristics in the composite was observed to be substantial. This caused the composite to have a better performance in flexure than non-reinforced ones and wood-flour composites. Several other studies have been done into using wood fibers in a polymer and other binding matrices. The main difficulty found in manufacturing wood-polymer composites is the incompatibility between the two materials due to their differing interaction with water. Selke et al. and Kim et al. [19], [20] performed detailed studies on this interaction and explored the use of chemical additives and coupling agents that improved the bond. Similarly, in the case of wood-lime composites, treatments like boiling and alkaline exposure can be used to modify the surface of the fibers [10]. This treatment removes the hemicellulosic and starch compounds on the surface and enhances the 25 bonding characteristics. Therefore, the high hydrophilicity of wood and other cellulosic fibers can be reduced with appropriate treatment and used as reinforcing elements in a variety of products. 2.2.2 Major challenges in bio-composite production Bio-composites are advantageous in terms of being eco-friendly, sustainable, strong and biodegradability. However, the products designed using natural cellulosic or lignin fibers suffer from problems such as high water absorption, shrinkage, incompatibility with cement particles and deterioration in the long run [21]. As described earlier, natural fibers contain many organic compounds like hemicellulose, tannins, fatty acids and starch on their surfaces which inhibit the setting of cement and other hydrating binders around it [22]. Another prevailing problem in case of ligno-cellulosic fibers is their degradation under highly caustic environments. The pH of cement and lime-based binders can go up to 13 and therefore be highly corrosive in nature. The organic components in the fibers also undergo deterioration because of the heat released from the hydration process. Therefore the fibers may suffer from increase in porosity and loss in strength due to the harsh environment [23]. The hydrophilicity of natural fibers due to the presence of cellulose and hemicellulose renders them with high water absorption capacity. This causes a dimensional instability in the fiber-matrix bonding. The issue of drying shrinkage in concrete and other cementing compounds as they age also induces a dimensional incompatibility in the composite. All these describes issues must be kept in mind when designing a bio-composite. The following section discusses a technique that can be adopted to solve some of these issues [21]. 26 2.2.3 Binders: Composition and properties As discussed in the last section, for utilising the full reinforcing potential of natural fibers, one needs a compatible binding matrix. Many previous studies have shown that lime-based binders are compatible with ligno-cellulosic aggregates [24]–[26]. Lime has been used in the manufacture of hemp concrete in several studies. It is shown to not have any major compatibility issues with the natural fibers. Lime is also known to be a sustainable alternative to cement because of the lower carbon footprint associated with its production and its ability to absorb atmospheric carbon dioxide to precipitate calcium carbonate [27], [28]. Gaseous CO2 diffuses through the pores in the mortar and dissolves in the pore water. Then the calcium hydroxide in the mix dissolves in the pore water and the reaction between CO2 and Ca(OH)2 give rise to CaCO3 crystals [28]. This inherent property of lime to form calcium carbonate crystals also contributes to a strength increase with age in hempcrete. Despite the advantages of the carbonation phenomenon, lime binders often suffer from delayed setting. Hydrated lime is often mixed with mineral additives like pozzolana or cement to accelerate the process of setting and hardening [29]–[31]. The addition of metakaolin to air lime has been extensively studied and it has been found that the addition accelerated the hardening process by introducing hydraulicity. Even in the presence of high humidity conditions and poor availability of carbon dioxide, the lime-metakaolin binders achieved considerable strength [31]. In another study on the effect of pozzolana on lime plasters, it was inferred that the thermal and hygric properties of the hybrid binders were either comparable or better than the pure lime mixes [30]. On an investigation on calcined gypsum-lime-metakaolin pastes, each component interacted synergistically to enhance the properties of the mortar. The addition of metakaolin caused as much 27 as three times increase in the compressive strength of the mortars. Metakaolin had significant role in the construction of the matrix structure [29]. When metakaolin or any other pozzolana is incorporated into air lime mixes, the main reactions demonstrated to take place are hydration, carbonation and pozzolanic reaction [32]. When there is no direct reaction happening between lime and the pozzolana, depending on the humidity and the availability of carbon dioxide, hydration and carbonation may compete. High humidity and moisture content promote the hydration reaction while dry conditions tend to favour carbonation reaction. Although the reaction between metakaolin and lime promotes faster hardening and helps in strength gain, most of the strength gain depends on hydration reaction and the stability of the hydrated phase. Therefore, lime-pozzolana mortars should be exposed to high moisture content in the early age to bolster hydration reaction. Cizer et al. [33] in their study on the crystal morphology of lime mortars under accelerated carbonation maintained 95%RH to facilitate the hydration as well as carbonation reaction. 2.2.4 Bio-composite curing processes As described in the previous sections, in lime-pozzolana mixtures three main reactions take place, hydration, carbonation, and pozzolanic reaction. While hydration happens in the first few hours of mixing, carbonation and pozzolanic reactions are slower and contribute to strength gain as the mortar ages. In pozzolanic reaction, the free lime or calcium hydroxide in the mix reacts with the pozzolanic material (like metakaolin) to form CSH gel. And in carbonation reaction, the free lime reacts with carbon dioxide to from calcium carbonate. While naturally, the carbonation process may take place for several years due to the low concentration of carbon dioxide in the atmosphere, 28 it can be accelerated by curing it in a carbon dioxide chamber [33]. This increases the dissolution of carbon dioxide in the pore water and thereby improves the carbonation process. Accelerated carbonation curing has been adopted in several studies to improve early age strength gain in lime-based binders. In a study conducted by Chabannes et al. [34], bio-composite manufactured using rice husk and hemp were subjected to a high concentration of CO2 in an enclosure for 30 days. The mechanical performance of these specimens was then compared to the ones cured in the outdoor exposure for 10 months. They both exhibited similar compressive strength showing that the cubes cured under accelerated carbonation for a month attained the same carbonation attained after 10-month outdoor exposure. In another series of experiments, de Bruijn et al. [25] exposed the lime-hemp composites to accelerated carbonation by storing them in a controlled atmosphere of 4.5% CO2. Similarly, based on experiments run on accelerated and natural carbonation curing of vegetable fiber composites in a study, it was found that the mechanical properties of specimens subjected to the carbon dioxide environment were enhanced. SEM analysis of the microstructure in many studies has shown the precipitation of calcium carbonate from carbonation reaction in the pore structure and the improvement of fiber-matrix bonding characteristics through densification. Use of accelerated carbonation in the curing regime of light weight composites like hempcrete is a promising technique. It particularly assists in strength gain in porous lignocellulosic composites and preventing the incompatibility issues between the fiber and the binder compounds. This procedure opens up an avenue of sequestering carbon dioxide emitted from industries while improving the microstructure of these composites [35], [36]. 29 2.2.5 Bio-composite manufacture Several studies have demonstrated the use of waste wood into cement bonded composites. Wang et al. [37] proposed a novel value-added approach to transform waste wood from construction formworks into cement bonded particleboards. The wood waste was milled and sieved to segregate particles of a size which then were mixed with OPC and an accelerator and compressed to obtain a panel specimen. The particleboards complied with the International Standard for Mechanical strength and Dimensional stability with added benefits of noise and thermal insulation. It has been established through numerous research initiatives that waste wood can be upcycled into particleboards by combining with cement with added benefits. The low density of the boards renders them with low thermal conductivity and noise absorption qualities. CO2 curing helped them in the formation of additional carbonates in the matrix and thereby decreased the porosity. Other natural and artificial fibers can be used to reinforce the composite and improve the mechanical strength and toughness of the specimens [21], [38]–[41]. 2.2.6 Performance of bio-composites 2.2.6.1 Mechanical performance The performance of bio-composites under mechanical loading depends on various factors such as length of fibers, fiber-matrix bonding, matrix strength and testing setup. In one study, experiments with hempcrete show that under compression it can reach a value of 462 kPa while under flexure the highest value is 141 kPa [14]. Wood-cement composites with higher binder to aggregate ratio and low water to cement ratio rendered specimens with a flexural strength of 11.8 MPa [38]. ASTM C208 specifies the minimum requirement for mechanical performance for use as thermal 30 insulation. According to the standard, the minimum compressive strength and flexural strength to qualify as Grade 1 thermal insulation are 100 kPa and 276 kPa respectively [42]. a) Bending b) Compression Figure 2.1 Typical loading curves of hempcrete [43] Typical loading curves of hempcrete under bending and compression stress are shown in Figure 2.1. Under compression, hempcrete undergoes indefinite inelastic strain with increasing stress after a limited elastic deformation. Under bending, the material fails after experiencing a large deformation [43]. The bio-composites discussed here all respond similarly to the compression and bending loads due to their similar porous and fibrous structure. 2.2.6.2 Thermal performance The low density and porous structure of bio-composites provides them with added benefits of thermal insulation properties. Composites manufactured using hemp, saw dust, wood powder and other cellulosic and lignin-based fibers, all have been analysed for their thermal performance and their thermal conductivity values are summarised here (table 2.1) [9], [11], [44]–[46]. 31 Table 2.1 Thermal conductivity values of common materials Material Density (kg/m3) Thermal conductivity, λ (W/mK) Hemp-lime composite 233-388 0.074-0.103 Sawdust-lime-composite 473-702 0.046-0.052 Binderless cotton stalk fiberboard 150-450 0.0585-0.0815 Wood 450-630 0.151 Fiberglass 24-120 0.034-0.047 Rockwool 80-200 0.025-0.035 Expanded perlite 78-224 0.0477-0.0616 32 Chapter 3: Materials and Testing 3.1 Bio-composite ingredients 3.1.1 Binder A binder that is compatible with cellulosic and lignin materials was designed with the aim to build a durable and sustainable bio-composite. The binder was chosen in such a way that the chemical composition does not interfere with the properties of the wood. Some of the key aspects that were considered during this process were the behaviour of wood elements in a caustic environment, the bonding between the wood and the binder and the sustainability of the binder. The binder that has been utilised in this study comprised of hydrated lime and metakaolin. The composition and the properties of these components are explained in the following sections. 3.1.1.1 Lime The lime used in this work is hydrated dolomitic lime with the chemical composition of calcium magnesium hydroxide (Ca(OH)2MgO) (Table 3.1). Bulk density of the lime here is 750 kg/m3. Table 3.1 Composition information of Dolomitic lime used in the study Component % by weight Calcium Hydroxide >58% Magnesium Hydroxide >38% Dolomite <1% Magnesium oxide <1% Crystalline Silica N/A It is procured from the company Graymont Limited. This dolomitic lime is manufactured by the calcination of high purity dolomitic limestone, which is then subjected to pressure hydration and 33 subsequently milled [47]. The acquired lime does not contain more than 0.5% of residues retained on a 600-µm sieve (ASTM C141/C141M [48]). 3.1.1.2 Metakaolin Metakaolin used in this work is supplied by Whitemud Resources Incorporated. This raw material is manufactured by the calcination of aluminium silicate (clay) procured from open pit mines. Due to the nature of its source, it is classified as a Type N pozzolan [49]. Detailed chemical composition is given in Table 3.2. Bulk density of metakaolin here is 800 kg/m3. Table 3.2 Composition information of metakaolin used in the study Component % by weight Kaolin, calcined >75% Total quartz (SiO2) 18-20% Fine Quartz (SiO2) < 4µm <3% Fine Quartz (SiO2) < 2.5µm <1.5% 3.1.1.3 Additives A variety of other additives were initially considered to replace some of the metakaolin in the binder. This was done to find cheaper and locally available alternatives to metakaolin. Several factors such as availability, cost and compatibility were reviewed. Two main additives eventually used for the study were wood ash and magnesium oxide board waste. Both the additives were available locally in Vancouver. Their chemical composition was found to be similar to that of the main binder components, lime and metakaolin. In addition, as by-products of a waste recycling stream, they were found to be more sustainable than metakaolin. 34 a) Wood ash Wood ash is obtained from the incineration of wood waste. The size of its particles ranges from 0.3 µm to 630 µm with an average size of 20 µm. An XRD analysis on the wood ash showed that the composition is predominantly silica (Figure 3.1). Figure 3.1 XRD results on wood ash b) Magnesium Oxide board waste This additive is obtained as a waste product in the manufacture of magnesium oxide boards. Chemical analysis of this material showed that it contained dolomite (Calcium magnesium carbonate) and silica (Figure 3.2). Its particle size ranged from 0.4 µm to 830 µm with an average size of 70 µm. 02000400060008000100001200014000Counts10 20 30 40 50 60 70 802ThetaMadhu_woodash - Madhu_woodash.raw (X-Offset) - Start: 3.012 ° - End: 80.035 ° - Step: 0.029 ° - Step Time: 100.10 sPDF 00-046-1045 - Quartz, syn - Si O2PDF 01-084-0752 - Albite - Na Al0.91 Si3 O8PDF 00-005-0628 - Halite, syn - Na ClPDF 04-003-2900 - Hematite, syn - Fe2 O3PDF 04-007-8659 - Calcite, syn - Ca ( C O3 )35 Figure 3.2 XRD results on magnesium oxide board waste 3.1.1.4 Alkali activators Sodium hydroxide (NaOH) was used as an alkali activator solution in this study. NaOH of 8 M concentration was utilised to activate the metakaolin in the mix. Alkaline activation of metakaolin is known to improve the microstructure of the matrix by the formation of polymeric alumino-silicates. High-early strength, low shrinkage and enhanced durability are some of the other advantages of employing alkali activation of metakaolin [23], [50], [51]. This could be clearly observed in the preliminary studies on binder pastes. However, it is later found that the sodium hydroxide is detrimental to the cellulosic and lignin compounds present in the wood chips. Hence NaOH is used in only certain mixes. 0100020003000400050006000700080009000Counts10 20 30 40 50 60 70 802ThetaMadhu_MgO - Madhu_MgO.raw - Start: 3.000 ° - End: 80.023 ° - Step: 0.029 ° - Step Time: 100.10 sPDF 04-008-0789 - Dolomite - Ca Mg ( C O3 )2PDF 00-008-0479 - Magnesite, syn - Mg C O3PDF 00-046-1045 - Quartz, syn - Si O2PDF 01-073-8515 - Ravatite, syn - C14 H1036 3.1.2 Fibers The fibrous part of the bio-composite consists of wood chips. These wood chips are obtained from waste wood from demolished decks and roofs. The wood pieces collected from various sites in British Columbia are then sent through a series of chippers at the UBC Forestry facility and UBC Civil engineering Materials lab to arrive on the required size. The wood used in this project is predominantly Cedar. Based on a preliminary study carried out in collaboration with the start-up Calmura Natural Walls, cedar was found to work better in a bio-composite than some of the other locally available wood and hence was chosen as the fibrous component in this research. 3.2 Study on binder performance 3.2.1 Mixture design Different binder compositions were experimented on before producing bio-composite specimens by varying the proportion of lime (L), metakaolin (MK), wood ash (W) and magnesium oxide waste (M). Binder pastes of different compositions were cast and tested for this set of preliminary studies. Initially the L/MK proportion is varied to produce five different compositions, which are 30/70, 40/60, 50/50, 60/40 and 70/30. Three mixes from this lot were further combined with wood ash and magnesium oxide waste (Table 3.3). A constant water-to-binder ratio of 0.5 was maintained for all the mixes. The mix-design by weight is then calculated based on the contribution of each component and their density. 37 Table 3.3 Mix proportions by weight of binder pastes Mix designation Binder materials Total NaOH /Binder Water/Binder Lime /Binder Metakaolin /Binder Wood ash /Binder MgO waste /Binder 70L-30MK-A 0.7 0.3 - - 1 0.04 0.5 60L-40MK-A 0.6 0.4 - - 1 0.04 0.5 50L-50MK-A 0.5 0.5 - - 1 0.04 0.5 40L-60MK-A 0.4 0.6 - - 1 0.04 0.5 30L-70MK-A 0.3 0.7 - - 1 0.04 0.5 60L-35MK-5W-A 0.6 0.35 0.05 - 1 0.04 0.5 50L-45MK-5W-A 0.5 0.45 0.05 - 1 0.04 0.5 38 40L-55MK-5W-A 0.4 0.55 0.05 - 1 0.04 0.5 60L-35MK-5M-A 0.6 0.35 - 0.05 1 0.04 0.5 50L-45MK-5M-A 0.5 0.45 - 0.05 1 0.04 0.5 40L-55MK-5M-A 0.4 0.55 - 0.05 1 0.04 0.5 60L-40MK 0.6 0.4 - - 1 - 0.5 3.2.2 Casting technique The binder paste was cast into several cubes of size 50mm. A simple mixing procedure was followed by dry mixing the binder components first and then slowly adding Sodium hydroxide. After that water was added slowly and mixed for a couple of minutes. The mix was then immediately transferred to moulds coated with releasing agents and compacted using a vibrating table. 39 3.2.3 Curing technique The binder cubes were kept in the ambient lab temperature and humidity for a few hours (upto 4) till the binder paste was set completely. Then a set of cubes were transferred into a carbon dioxide chamber for 7 days. The CO2 concentration inside the chamber was maintained at 4% (accelerated carbonation), the temperature at 20°C and humidity at 90%-95%. Another set of cubes were left on the outside in the laboratory conditions (natural carbonation) of temperature 20°C and approximate humidity of 50%RH. 3.2.4 Mechanical Testing The cubes were tested (Figure 3.3) under compression at 7, 28 and 56 days according to the specifications given in ASTM C109 (Standard Test Method for Compressive Strength of Hydraulic Cement Mortars)[52]. Figure 3.3 Compression test setup for testing binder paste cubes 3.2.5 Chemical and microstructure studies The paste samples were analysed to characterise the reactions leading to strength gain using various methods like XRD, SEM and EDS. Each analysis technique is detailed out in this section. 40 X-ray Powder Diffraction is an analytical technique used to find the phase identification details of a crystalline material. A piece of solidified binder was extracted, powdered into fine material and then laid out on a slide as a homogeneous layer for analysis in the XRD machine. XRD analysis was done on the paste samples at 28 and 56 days. Scanning Electron Microscopy (SEM) analysis involves the use of a focussed beam of electrons on a specimen’s surface to study its topography. Higher magnification of the order of up to 30000x can be used to observe the calcium carbonate crystals and other binding phase components. Another utility available with the SEM is EDS (Energy Dispersive X-Ray Spectroscopy). In EDS analysis, the backscattered electrons from the surface of the specimen are examined to identify the elements and characterize the quantitative composition on the surface. Both SEM and SEM-EDS were performed on different compositions at different ages of 14, 28 and 56 days. One of the preliminary chemical tests to check the formation of calcium carbonate is the use of phenolphthalein indicator. Phenolphthalein is usually employed as a pH indicator that shows a pink colour if the pH is higher than 8.2 but doesn’t show any colour if the solution is acidic (pH 0 to 8.2). This indicator was sprayed on cut specimens at different ages. When the indicator interacts with unreacted lime (which has high pH), it turns pink and hence revealing the uncarbonated regions. Similarly, when the indicator interacts with carbonate formation (low pH), it doesn’t exhibit any change in colour. 41 3.3 Study on bio-composite panels 3.3.1 Manufacturing process 3.3.1.1 Screening The first step of the manufacturing process was the screening of the wood chips for suitable length and width. This step was necessary to keep the chips being used of consistent quality. Based on the desired thickness of the specimens, wood chips were subjected to screening on 3 different sieves. 1. The coarse sieve filters out the chips of size greater than 50 mm (length and width). This was done to remove the bigger pieces which are later sent through the chipping facility. 2. In the second step, the wood chips are passed through a square or slotted sieve of 7 x 5 mm dimension. Chips of this size were considered ideal based on the thickness and size planned for the finished product. 3. The last step of sieving is done to remove the wood chips that are smaller than the intended size which is typically fine and coarse saw dust. Saw dust delays the hardening process of the bio-composite specimens and affects the porosity of the material and hence essentially removed from the mix. a) Coarse sieve b) Saw-dust sieve 42 c) Fine sieve d) Fine sieve showing the slots and wood chips Figure 3.4 Sieves used for screening wood chips in this work 3.3.1.2 Mixture design Two main compositions were isolated from the preliminary binder results (refer to section 4.1). The binders that performed significantly better than others in compression were the compositions with lime to metakaolin ratio of 60/40 and 50/50. These compositions are represented by 60L-40MK and 50L-50MK hereon. Four more variations of these mixes were prepared by replacing 5% of metakaolin with wood ash and magnesium oxide board waste. The wood ash variants are represented by 60L-35MK-5W and 50L-45MK-5W while the MgO waste variants are represented by 60L-35MK-5M and 50L-45MK-5M. Therefore, a total of 6 different binder compositions were used in the manufacture of bio-composite samples and studied (Table 3.5). Along with these 6 mixes, one sample mix was made using an alkali activator (60L-40MK-A). The use of sodium hydroxide was limited in this study due to the observed deterioration of wood chips on alkali exposure. 43 Table 3.4 Mix designation and composition Mix designation Binder materials Total NaOH /Binder Water/Binder Lime /Binder Metakaolin /Binder Wood ash /Binder MgO waste /Binder 60L-40MK 0.6 0.4 - - 1 0 1.5 50L-50MK 0.5 0.5 - - 1 0 1.5 40L-60MK 0.4 0.6 - - 1 0 1.5 60L-35MK-5W 0.6 0.35 0.05 - 1 0 1.5 50L-45MK-5W 0.5 0.45 0.05 - 1 0 1.5 60L-35MK-5M 0.6 0.35 - 0.05 1 0 1.5 50L-45MK-5M 0.5 0.45 - 0.05 1 0 1.5 60L-40MK-A 0.6 0.4 - - 1 0.04 1.5 Mix design procedure: From the review of literature on hempcrete and similar ligno-cellulosic bio-composites, the density of the bio-composite in this study was adopted as 360 kg/m3. The contribution of cedar in this was set to be 152.7 kg/m3 based on a primary investigation done in collaboration with Calmura Natural 44 Walls. This made the contribution of binder to the bio-composite density to be 207.3 kg/m3. Further, the water to binder ratio was selected as 1.5 to compensate for the absorptive property of cedar pieces. Sample mix designs for two compositions (with and without NaOH) are shown in Table 3.6 and 3.7. Table 3.5 Sample mix design for 60L-40MK Binder materials Cedar NaOH Water Lime Metakaolin Wood ash MgO waste [%] by weight 60 40 0 0 - - - [kg/m3] 124.4 82.9 0 0 152.7 0 310.95 Table 3.6 Sample mix design for 60L-40MK-A Binder materials Cedar NaOH Water Lime Metakaolin Wood ash MgO waste [%] by weight 60 40 0 0 - 4 - [kg/m3] 124.4 82.9 0 0 152.7 8.29 310.95 3.3.1.3 Mixing and casting The standard size for the bio-composite specimens was selected with reference to ASTM standards C208 and C209 that specify standard specifications and testing methods for cellulosic fiber insulating boards [42], [53]. The bio-composite in this research work fell in the purview of the 45 material definition in C208 and C209. The specimen size is chosen so that the size is large enough to be representative of the actual panel production process (especially compaction) as well as the curing process. At the same time, it was also considered that it could be cut to obtain the required samples for compression, flexure and thermal testing as specified in ASTM C209. After screening, wood chips are mixed with an equal amount of water (by mass). Once this mixture is run in the mixer for 2-3 minutes, the binder materials (lime and metakaolin) are added. The remaining measured water is also added at last and the mix is stirred for 2 more minutes. Once the slurry of wood chips and binder is ready, it is poured into a mould coated with a releasing agent. Before compaction, the slurry is distributed evenly around the mould with the help of a gardening fork such that the fibers have no particular orientation in the form. Over the distributed slurry, a wooden slab that fits the mould perfectly is placed. The slab is then hammered down till the panel reaches the desired thickness of 75mm. After compaction, the frame is removed carefully, and the panel is immediately transferred into the carbonation chamber where it is cured for the next 7 days. There is no issue of flowing since the material retains the shape even after the removal of form. A set of panels were also cured under ambient room temperature and humidity allowing natural carbonation for comparison. 46 Figure 3.5 Mould used for producing panels Figure 3.6 Cast panels stored for drying after curing 3.3.2 Curing process Similar to the curing of binder paste cubes in (section 3.2.3), a carbonation chamber was employed to cure the specimens for the first 7 days after casting. The chamber had a carbon dioxide concentration of 4% and maintained at a temperature of 25 degrees Celsius and 90% - 95% relative humidity (RH). Note that the panel needed a support on the top for the first 24 hours to prevent the spring back of the wood fibers when the compaction load was removed. After curing in the high carbon dioxide environment for 7 days, the panels were transferred and stored in the ambient 47 laboratory conditions of 50%RH and 22°C temperature. The specimens slowly dry up in these conditions and were ready to be tested at 28 and 56 days. Another set of panels that were cured in laboratory conditions (without exposure to high carbon dioxide environment), underwent natural carbonation and were tested at 28 and 56 days. The carbonation chamber used here was Forma 29 cu ft Reach-In Incubator of model 3950 from the company ThermoFisher Scientific. The incubator had humidity control, temperature control and carbon dioxide control. 3.3.3 Sampling and cutting Each specimen was divided into beams and prisms of size as required for the testing recommended by the ASTM standards. Compression and thermal tests were done on square prisms of size 100 mm x 100 mm x 70 mm. Flexural tests were done on beam type specimens of size 381 mm x 76 mm x 70 mm. The above sizes and the testing procedures were adopted from ASTM C209, C165 and C518 [53]–[55]. The sampling map was prepared to be able to obtain test samples from different regions of the panel. This was done to study the variation of strength and other mechanical properties across the length of the panel due to the influence of edge effects and the level of carbonation. The image below (Figure 3.5) shows the sampling map of the bio-composite panels. Samples labelled 1, 2 and 4 were used for flexural tests, samples 3-1, 3-2, 5-1 and 5-2 were used for compression tests and sample 3-3 and 5-3 were used for thermal conductivity tests. The sample cutting is carried out using a band saw and a chop saw. 48 a) Specimen designation b) Marked specimen ready to be cut Figure 3.7 Sampling plan with specimen designation 3.3.4 Testing 3.3.4.1 Compressive test The compressive tests were done on the bio-composite specimens of size 100mm x 100mm x 70mm at 28th and 56th day. As mentioned in the previous section, ASTM C209 and C165 were used to establish the conditions and parameters for conducting the test (Figure 3.6a). According to the adopted procedure, the specimen was compressed till it was 90% of its initial thickness. The load at that compression was noted and used to characterise the compressive behaviour of the material. It is assumed that the 10% compression happens at the point of onset of inelastic strain. 49 a) b) Figure 3.8 a) Compression test setup and b) flexure test setup 3.3.4.2 Flexural test The flexural tests were done on the 28th and 56th day. The flexure strength of the specimens was obtained by subjecting them to a center point bending test. The test was conducted on beams of size 381mm x 76mm x 70mm according to ASTM C209 (Figure 3.6b). The modulus of rupture was then calculated using the failure load as shown below [42]. 𝑀𝑂𝑅 =6𝑃𝑡2 Where MOR = Modulus of rupture, MPa P = transverse failure load, N t = thickness, mm 3.3.4.3 Thermal testing Thermal conductivity of the bio-composite specimens was found using the Heat Flow Meter Apparatus in accordance with the standards ASTM C208, C209 and C518. ASTM C518 50 specifically outlines the procedure for the measurement of steady state thermal transmission through flat slab specimens using a heat flow meter apparatus. This method had been known to work in a plate temperature range of -195°C to 540°C at 25 mm thickness and at a range of 10°C to 40°C at 250 mm thickness. Hence the procedure outlined in the code was applicable to the bio-composite specimens in this study. The Heat flow meter apparatus adopted in this testing regime is shown in Figure 3.7. a) Conceptual setup (Source: ASTM C518) b) Laboratory setup Figure 3.9 Heat flow meter As shown in the Figure, the specimen is sandwiched between two parallel hot and cold plates. Two heat flux transducers are placed on the inner face of the plates in contact with the specimen. Hot plate apparatus is used as the heating plate and thermoelectric cooler plate is attached with the top plate. The two plates are maintained at a constant temperature difference of 25±5°C and the voltage required to maintain this temperature difference is measured through the transducers. The specimen is wrapped with cotton insulation to prevent heat losses through the edges. The specimens were also conditioned for 24 hours in 50%RH and 20°C to render all the specimens with similar moisture content and temperature. 51 The heat flux output through the two faces of the plate and along with the plate temperature are used to calculate the thermal conductivity of the specimens according to the following formula. 𝜆 (𝑊/𝑚𝐾) =𝑄𝐿Δ𝑇 Where Q is the heat flux through the metered area (area covered by the sensor) in W/m2 L is the separation between the hot and cold plate assembly during testing in m ΔT is the difference in temperature across the thickness of the specimen in K 3.3.4.4 Microstructure studies The interaction of ligno-cellulosic materials with the alkaline binder induces various complex reactions in the composite matrix. To understand these reactions and examine them in detail, chemical and microstructure analyses were done on samples from the bio-composite akin to the binder paste samples (section 3.2.5) 3.3.4.5 Chemical studies Phenolphthalein indicator was employed here to characterise the carbonation in bio-composite specimens. It was sprayed on the specimens at different ages when the specimen was cut to be tested for mechanical and thermal performance. The width of the pink patches was measured and noted down along with its position. Based on the level of carbonation at different regions of the panel, a carbonation map was drawn. The carbonation map of different specimens at different ages was obtained and compared. 52 Chapter 4: Results and discussion 4.1 Results from binder studies 4.1.1 Mechanical test results All the results of compression tests on binder paste cubes are shown in Figure 4.1 and 4.2. Figure 4.1 summarises the compressive strength of binder cubes of different compositions cured in ambient laboratory conditions. They underwent natural carbonation (NC) and drying at 50%RH and 20°C. It can be noticed here that the strength of cubes increased with decrease in the lime/metakaolin ratio but only up to a certain point (50:50) after which the decrease negatively affected the strength. 60L-35MK-5M and 50L-50MK were the best performing mixes. Figure 4.1 Compressive strength of binder paste cubes of different composition subjected to natural carbonation 0.05.010.015.020.025.0Compressive strength (MPa)Binder compositionCompressive strength vs Binder composition(Natural carbonation)7th day 28th day 56th day53 There was some strength loss observed between 7th and 56th day in certain mixes. This could be due to the formation of shrinkage cracks. Figure 4.2 summarises the compressive strength of binder cubes of different compositions cured in a high carbon dioxide environment. They were subjected to an accelerated carbonation (AC) regime of curing and hence differed in behaviour from the NC cubes. It is observed from the Figure that the strength increased with decrease in lime-metakaolin ratio. Like NC cubes, the strength had a decreasing trend once the lime metakaolin ratio reached 40:60. Figure 4.2 Compressive strength of binder cubes of different composition subjected to accelerated carbonation There was a significant difference in the compressive strength of the binders cured in lab conditions (NC) than the ones cured in high carbon dioxide environment (AC). The maximum strength some of the NC mixes reached was as much as 20 MPa while in case of the AC mixes it 0.02.04.06.08.010.012.014.016.0Compressive strength (MPa)Binder compositionCompressive strength vs Binder composition (Accelerated carbonation curing)7th day 28th day 56th day54 was only 13 MPa. This might be due to the instability induced in the matrix due to accelerated carbonation. The interference of various reactions like hydration, carbonation, alkali-activation and possible pozzolanic reaction happening simultaneously might be the reason behind this strength variation. It was also observed that the cubes cured in the carbon dioxide chamber had wet, not fully dried regions (Figure 4.3). This could be another reason for the low strength of AC cubes. Figure 4.3 Wet regions near the centre of the cube The compressive strength of cubes increased with increase in the lime content for both natural and accelerated carbonation up to a point (Figure 4.3). Further increase caused a decrease in the strength. This might be due to the lower availability of free lime as the cubes age to form carbonates or to react with the pozzolans. The mix with the highest (30L-70MK) and with the lowest (70L-30MK) hydration potential exhibit very low strength. While the earlier can be attributed to high lime but insufficient carbonation, the latter one could be due to low hydration and insufficient alkali-activation. The evolution of strength of different mixes with varying lime-to-metakaolin ratio is shown in Figure 4.4. At 7 and 28 days, for cubes that were subjected to accelerated carbonation (Figure 55 4.4a), the highest strength is observed for the lime-to-metakaolin ratio of 1 (mix 50L-50MK). However, at the age of 56 days the highest strength is seen for the L/MK ratio of 1.5 (60L-40MK). Similarly, in the case of cubes that were cured under laboratory conditions (Figure 4.4b), at 7,28 and 56 days the highest strength is exhibited by the mix with the L/MK ratio of 1 (50L-50MK). In general, when lime and metakaolin are combined, due to the high reactivity of metakaolin, pozzolanic reaction dominates the carbonation reaction. Under laboratory curing conditions, the pozzolanic reaction will happen early while carbonation is much slower and would take place later than 28 days. Therefore, in case of NC cubes, the strength increased from 7th day to 56th day due to pozzolanic reaction. The optimum mix that gave the highest strength in these conditions is 50L-50MK-A. In the case of AC cubes, the carbonation reaction dominated the early days. Exposure to high concentration of carbon dioxide accelerated the process of formation of carbonate crystals in the paste. Therefore, the pozzolanic reaction was the delayed reaction and happened slower than carbonation. At 7 days, when the pozzolanic reaction hadn’t started yet, the highest strength is achieved by the mix 50L-50MK. However, at 56 days, pozzolanic reaction products might compete with the carbonation products leading to an instability. Therefore, the mix with lower pozzolana (60L-40MK) achieves higher strength. 56 a) Accelerated carbonation (AC) b) Natural carbonation (NC) Figure 4.4 Influence of lime-to-metakaolin ratio on the strength of binder pastes cured in carbonation chamber (a) and laboratory conditions (b) 0.02.04.06.08.010.012.014.00 0.5 1 1.5 2 2.5Compressive strength, MPaLime-to-metakaolin ratio7th day28th day56th day0.05.010.015.020.025.00 0.5 1 1.5 2 2.5Compressive strength, MPaLime-to-metakaolin ratio7th day28th day56th day57 4.1.2 Microstructure studies The SEM micrographs of binder samples at 28 and 56 days revealed important information about the microstructure and the reaction products. It was observed that the all the paste samples irrespective of their composition contained large regions of unreacted lime and metakaolin particles (dark patches). a) b) c) d) Figure 4.5 SEM images showing regions of unreacted lime and metakaolin in 60L-40MK-A – a) and c) and 40L-60MK-A – b) and d) 58 The corroded structure (white patchy regions) corresponds to calcium carbonate formation. Corroded structure is observed when the carbonate crystals have not formed fully and indicate that the carbon dioxide has just attacked the surface and induced carbonation process. There was large carbonate formation (yellow arrows in Figure 4.5a and b) observed around cracks and crevices. This means that the carbon dioxide could penetrate the hardened binder only near cracks and hence unavailable for most of the remaining regions. Figure 4.5c and d show all the components of the binder in detail. On comparing the mixes with high metakaolin content (30L-70MK-A) and high lime content (60L-40MK-A) in Figure 4.6, the latter evidently contained higher amount of calcium carbonate formation. 60L-40MK-A also comprised of bigger carbonate crystals (red arrows in Figure 4.6). a) 30L-70MK-A b) 60L-40MK-A Figure 4.6 SEM images showing carbonate crystals in different compositions 59 a) b) c) d) e) f) Figure 4.7 SEM images of binder phase of mix 60L-40MK without sodium hydroxide – (a), (c), (e) and 60L-40MK-A with sodium hydroxide – (b), (d), (f) at 56 days 60 The microstructure of mix incorporated with NaOH was compared with the mix without any alkali activators. On comparing the micrographs of 60L-40MK-A and 60L-40MK, a similar structure is observed. Figure 4.7 shows the SEM images of these two mixes at different magnifications. An almost similar carbonate formation (white patches) is observed in both mixes. However, at higher magnification, the matrix of 60L-40MK-A could be seen with a visibly denser structure because of the products of alkali activation. Alkali activation of metakaolin produces polymeric alumino-silicates that make the matrix denser and stronger. 4.1.3 X-Ray Diffraction (XRD) Analysis XRD analysis on the binder samples revealed the presence of calcite indicating the formation of carbonate. Different phases of carbonate like calcite and vaterite were observed in the results which demonstrates that the carbonation happens in stages and that the complete transformation has not happened yet (Figure 4.8) [33]. The other major constituents found in the sample were silica and magnesium hydroxide. An interesting observation here is that the XRD graph does not significantly change with change in the composition of the mix. Similar peaks were formed for all the binder mixes. 61 a) 60L-40MK-A b) 60L-35MK-5W-A Figure 4.8 XRD results of binder different mixes 4.1.4 Chemical analysis A simple way to monitor the carbonation process in the cubes was to spray phenolphthalein indicator over the cross section of the surface. The indicator was used to find the extent of carbonation reaction in the specimens. The specimens subjected to accelerated carbonation showed a higher extent of carbonation than the ones subjected to natural carbonation. In the Figure 4.9, the 0200040006000800010000Counts10 20 30 40 50 60 70 802ThetaMadhu_b10 - Madhu_b10.raw - Start: 3.000 ° - End: 80.023 ° - Step: 0.029 ° - Step Time: 100.10 sPDF 01-089-1304 - Calcite, magnesian, syn - ( Mg0.03 Ca0.97 ) ( C O3 )PDF 00-007-0239 - Brucite, syn - Mg ( O H )2PDF 00-046-1045 - Quartz, syn - Si O2PDF 00-060-0483 - Vaterite, syn - Ca C O3010002000300040005000600070008000Counts10 20 30 40 50 60 70 802ThetaMadhu_b6 - Madhu_b6.raw - Start: 3.000 ° - End: 80.023 ° - Step: 0.029 ° - Step Time: 100.10 sPDF 00-046-1045 - Quartz, syn - Si O2PDF 04-011-5938 - Brucite, syn - Mg ( O H )2PDF 01-089-1304 - Calcite, magnesian, syn - ( Mg0.03 Ca0.97 ) ( C O3 )PDF 04-015-4421 - Gypsum - Ca ( S O4 ) ( H2 O )262 white regions that do not turn pink are carbonated and the regions that have turned pink are not carbonated and hence contain unreacted lime. The samples subjected to accelerated carbonation contain broader white strips (Figure 4.9b) near the edge while the others have thinner white regions (Figure 4.9a). a) b) c) d) Figure 4.9 Carbonated (white strips) and non-carbonated (pink) parts of NC cubes – a), c) and AC cubes – b), d) 63 4.2 Results on bio-composite panels 4.2.1 Mechanical test results The mechanical properties of bio-composite specimens were measured through compression and flexure tests. The typical behaviour of the samples under compression and bending are shown in the Figures 4.10 and 4.11. Under compression, the specimen initially undergoes elastic deformation (green line in Figure 4.10). The compressive stress of the material after the onset of inelastic strain is taken as the compressive strength of the material. In most of the tested samples, the samples didn’t fracture under compression after the onset of inelastic deformation. Further increase in the loading only caused an increase in the compressive stress continuously. This is due to the compaction of the porous structure of the bio-composite. Thus, the bio-composite has a quasi-ductile behaviour unlike conventional concrete whose failure is sudden and brittle in nature. Figure 4.10 Typical loading curves under compression -500501001502002503000 0.02 0.04 0.06 0.08 0.1 0.12 0.14Compressive stress, kPaCompressive StrainCompressive strength 64 The flexural strength of the bio-composite was calculated from the maximum load reached under bending (Figure 4.12). The initial steep slope of the bending curve shows that the material is quite brittle in nature under flexure. Figure 4.11 shows the failed flexure specimen. From Figure 4.12, it is inferred that the failure mode of the bio-composite is ductile in nature. It does not fail immediately after the peak stress. Instead, the material undergoes softening after the peak stress which could be due to the redistribution of stress through the wood chips. Figure 4.11 Beam specimen before testing (a) and after testing (b) Figure 4.12 Typical loading curve under bending -20.000.0020.0040.0060.0080.00100.00120.00140.00-1 0 1 2 3 4 5 6Bending stress, kPaDisplacement, mm65 On comparing the mechanical performance at 28 days and 56 days, there’s an increase in the compression strength (Figure 4.14). This might be due to the increase in the amount of carbonation with age. At 56 days, all the compositions have performed better under compression meeting the minimum requirements of ASTM C208. However, the performance under flexure hasn’t improved significantly with age (Figure 4.13) and does not meet the specifications of ASTM C208. This shows that the carbonate formation has not helped the bending behaviour of the specimens. This could be due to the small size and the rigidity of the wood chips that prevent them from forming a flexible and strong out of plane bond. Another issue that might have affected the behaviour and strength of the bio-composite was the cutting process. It was noticed that some of the specimens lost material around the edges during cutting. Especially the chop saw used to cut the specimens was coarse and might have disturbed the structure from inside. Figure 4.13 Flexural strength of bio-composite specimens with age 0501001502002503000 28 56Flexural strength, kPaAge, days60L-35MK-5W50L-45MK-5W60L-35MK-5M50L-45MK-5M60L-40MK50L-50MK66 Figure 4.14 Compressive strength of bio-composite specimens with age The mechanical behavior of the bio-composite (woodcrete) panels is summarized in Figure 4.15, where the average flexural strength for each composition is plotted versus average compressive strength (with standard deviations). The average values and standard deviations for each mix are calculated based on the data obtained from 3 samples. The performance of various compositions shown in the graph is compared with the recommended values from ASTM C208 (blue line for bending and red line for compression). One can observe that most compositions have an appreciable performance under compression and meet the minimum expectations of the referred ASTM. However, even one of the strongest specimens (60L-35MK-5W) in compression reaches only a value of 60% of the recommended value from ASTM under flexure. Calmura Natural Walls, the start-up with whose collaboration this research work was performed had done several preliminary trials with the bio-composite. Although they had performed bending 0.0050.00100.00150.00200.00250.00300.000 28 56Compressive strength, kPaAge, days60L-35MK-5W50L-45MK-5W60L-35MK-5M50L-45MK-5M60L-40MK50L-50MK67 tests on their samples, the test was performed on smaller sample sizes. The well-performing mixes in these preliminary trials were adopted here for better investigation. a) b) Figure 4.15 Summary of mechanical behaviour of bio-composite specimens at 28 days (a) and 56 days (b) 0501001502002503003504000.00 50.00 100.00 150.00 200.00 250.00Flexural strength, kPaCompressive strength, kPaMechanical performance data of Bio-composite at 28 days 60L-35MK-5W50L-45MK-5W60L-35MK-5M50L-45MK-5M60L-40MK50L-50MK60L-40MK-AASTM C208 recommendedflexural strength0501001502002503003504000 50 100 150 200 250Flexural strength, kPaCompressive strength, kPaMechanical performance data of Bio-composite at 56 days 60L-35MK-5W50L-45MK-5W60L-35MK-5M50L-45MK-5M60L-40MK50L-50MKASTM C208 recommendedflexural strengthASTM C208 recommendedcompressive strength68 60L-40MK-A, the mix with NaOH, performed the best in compression. Despite its performance under compression, the specimen again lacked strength under flexure. The denser matrix of this mix due to alkali activation has only enhanced the compressive strength of the sample and not improved the ability of the specimen to resist bending. At 56 days, the flexural behaviour is quite similar to that of 28 days age (Figure 4.15a and b). While the average flexural strength has decreased from 80 kPa to 75.9 kPa, the average performance of bio-composite in compression has increased from 136 kPa to 203.7 kPa. It is also observed that the mix 60L-35MK-5M performed the least and the mix 60L-35MK-5W performed the best at 28 days as well as 56 days. The mixes that were naturally carbonated were also tested under mechanical loading but exhibited extremely poor behaviour with some of the specimens disintegrating during the cutting process itself. Figure 4.16 shows the broken specimen. a) b) Figure 4.16 Naturally carbonated specimen (disintegrated during cutting process) 69 Initially, it was planned to test the bio-composite specimens at 14, 28 and 56 days. However, this plan was later changed to 28 and 56 days because of the longer drying period of the specimens. At 14 days, it was observed that the bio-composite was not sturdy and could easily be disintegrated. 4.2.2 Thermal test results The thermal performance of bio-composite is tested using a heat flow meter apparatus as described in ASTM C518. Figure 4.17 summarises the thermal conductivity values obtained on different composition of bio-composites. The thermal performance of woodcrete has been compared with that of hempcrete of similar density, commercially available foam insulation boards and ASTM C208 specified values. The thermal conductivity values (λ values) are plotted against the corresponding density of the specimens with standard deviations measured on a sample size of 3. The density of the samples was in the range of 320 – 400 kg/m3 close to the designed density of 360 kg/m3. Figure 4.17 Thermal conductivity value of bio-composite samples at 56 days 00.010.020.030.040.050.060.070.080.090.1200 300 400 500λ-value (W/mK)Density (kg/m³)C60L-40MKC50L-50MKC60L-35MK-5WC50L-45MK-5WC60L-35MK-5MC50L-45MK-5MC60L-40MK-NaOHHempcreteASTM C208 recommendedvalueFoam insulation board70 It is seen that the thermal conductivity of the samples falls between 0.04 W/mK and 0.07 W/mK. Five out of seven mixes meet the ASTM recommended value (0.06 W/mK) for panels to be used as a wall insulation. For comparison, the thermal performance of the specimens is plotted with the hempcrete and foam insulation board values. It is observed that the woodcrete performs better than hempcrete of same density[34]. However, when compared to foam insulation boards, the woodcrete specimens are heavier and have higher conductivity values. An interesting observation made here is that all the mixes containing 60% lime (without NaOH) have a thermal conductivity value of around 0.05 W/mK while all the mixes containing 50% lime (without NaOH) have their thermal conductivity values closer to 0.06 W/mK. This could be due to higher metakaolin amount from in the latter mixes. Research has shown that the addition of metakaolin increases the thermal conductivity of lime mortars [56]. 4.2.3 Chemical/Microstructure studies 4.2.3.1 Scanning Electron Microscopy (SEM) analysis The following set of images show the SEM micrographs of the wood fiber and the bio-composite mixes (28 days). The first image gives us a close look at the topography of the wood fiber’s surface. The image shows the porous structure of the fiber that makes it highly desirable for light weight applications. The vascular tissues present in the fiber (blue arrows in Figure 4.18a) that are responsible for high water retention and hygroscopic properties can also be seen under SEM. When the bio-composite is hardened and dried and ready for testing, it is noticed that the outer exposed surface is quite harder and stronger than the unexposed parts. Therefore, during the extraction of samples for SEM analysis, samples were taken from a depth of 20 mm. This ensured 71 that the carbonation products were observed on the interior of the panel rather than just on the surface. a) Plain cedar b) 60L-40MK c) 60L-40MK-NaOH d) 50L-50MK e) 40L-60MK Figure 4.18 SEM micrographs of wood fiber (a) and bio-composite samples at 28 days (b to e) 72 The lighter white region in the pictures showing the binder components represents the carbonate formation. The darker region represents the unreacted lime and metakaolin. On comparing image (b) and image (e), it is noticed that the amount of carbonation is higher in 60L-40MK due to the higher volume of lime available. Image (c) shows the composition 60L-40MK-NaOH. It is observed in the image that the structure is denser due to the alkali activation of metakaolin. a) 60L-40MK b) 60L-35MK-5M c) 60L-35MK-5W d) 60L-40MK (Natural carbonation) Figure 4.19 SEM micrographs of bio-composite samples at 56 days 73 Figure 4.18 shows the SEM images obtained for the bio-composite at 56 days of age. It is observed that the microstructure of the binder phase has improved from 28 to 56 days (Figure 4.19a, b and c). The matrix is denser and has higher carbonate formation. However, the binder composition 60L-40MK cured under lab conditions (Figure 4.19d) and atmospheric carbon dioxide exposure shows a poorly formed microstructure. Several patches of unreacted materials can be found in the image. Individual crystals of carbonate and CSH formation are poor and hence explain the poor performance of the same under mechanical loading. 4.2.3.2 Energy Dispersive X-Ray Spectroscopy (EDX) Analysis Elemental mapping through SEM-EDX was obtained to study the distribution of basic elements in the reaction products and other compounds on the surface of the bio-composite samples. In Figures 4.20a, b and c, the elemental maps of a sample of mix 60L-40MK are shown. a) Calcium b) Silicon 74 c) Aluminium d) BSE Figure 4.20 SEM-EDX elemental maps of 60L-40MK mix along with BSE image In all the images, brighter the colour of the spot, higher is the concentration of the corresponding element in that spot. The bright blue spots in 4.20a (yellow arrows) correspond to unreacted lime lump while the lighter spots correspond to disintegrated lime particles (red arrow). It is observed in the figures 4.20b and 4.20c that regions with unreacted lime don’t have any silica (green arrows) or alumina compounds (blue arrows). This means that the lime lump has not undergone any pozzolanic reaction. However, in the Figure, the overlapping regions of blue, pink and yellow correspond to the product of pozzolanic reaction where calcium hydroxide has reacted with the silica and alumina present in the metakaolin. 4.2.3.3 Carbonation test The bio-composite panels after being cut into beams and prisms were sprayed with phenolphthalein indicator. The indicator showed pink colour when it interacted with a high pH substance and did not show any colour at neutral and acidic pH (Figure 4.21). The images below show this reaction. 75 a) b) Figure 4.21 Beam specimens a) well carbonated and b) poorly carbonated Some specimens that were poorly carbonated despite curing in carbonation chamber, were not considered for testing. On further investigation, it was found that the poor carbonation was because of stacking the panels one above the other in the chamber. After realising this problem, care was taken not to hinder the diffusion of carbon dioxide into the specimens. The size of the uncarbonated patch and their position across the panel were noted down while being sprayed upon by phenolphthalein. A carbonation map that shows the uncarbonated regions in a panel across the length and width was eventually made using this data. A common observation in all the samples is that the uncarbonated region increased as one moved from the edge to the centre. This might be due to the lesser penetration of carbon dioxide in the obscured regions closer to the centre. The specimens that were placed outside the chamber were subjected to natural carbonation and contained substantial regions of unreacted lime (Figure 4.21b and 4.22b). 76 a) Well carbonated b) Poorly carbonated Figure 4.22 Carbonation map showing the size of uncarbonated regions across the panel 0111287463010203040506070035135 235 335 416 515 550Width (mm)Length (mm)0-10 10-20 20-30 30-40 40-50 50-60 60-700111287463010203040506070035135 235 335 416 515 550Width (mm)Length (mm)0-10 10-20 20-30 30-40 40-50 50-60 60-7077 Chapter 5: Conclusion and future research 5.1 Conclusions The purpose of this study was to build a bio-composite using waste wood that is sustainable and affordable and could be utilized to build non-structural building components. The bio-composite was constructed by combining chipped wood pieces and a binding matrix containing lime and metakaolin. Preliminary investigation was done on lime-metakaolin pastes to arrive on a mix with optimised strength properties. This optimised mix was then adopted to build the final bio-composite. The bio-composite in this work was later tested for its mechanical, chemical and thermal properties. The compressive strength, flexural strength and thermal conductivity values of the specimens were then compared to the minimum requirements specified in the ASTM C208 for Grade 1 insulation panels. The microstructure of the specimens was also investigated to examine the bonding between the matrix and wood chips. The topography of the wood pieces and the matrix were observed using a Scanning electron microscope at 14, 28 and 56 days of age. The results from the mentioned tests were encouraging and summarised below. a) Lime and metakaolin can be combined to build a durable, compatible and strong binding matrix. The binder undergoes various reactions like hydration, carbonation, pozzolanic reaction and alkali activation to harden and attain high strength. b) The binder pastes of 60L-40MK and 50L-50MK were found to be the best performing in terms of compressive strength when the lime-metakaolin ratio was varied. These two mixes were then modified by addition of Magnesium oxide waste and wood ash. These mixes also performed comparable to the original ones. c) A bio-composite can be successfully manufactured by utilising waste wood chips and lime-metakaolin pastes. The wood chips, organic in nature, tend to form a compatible bond with 78 an inorganic matrix containing lime and metakaolin. SEM analysis revealed that the perforated topography of the wood pieces was modified because of the formation of reaction products of the binder. d) An effective mode of accelerating the strength gain in the bio-composite specimens was found. The specimens subjected to a high carbon dioxide environment (4%) underwent rapid strength gain. It was verified through phenolphthalein test and EDX analysis that the lime in the specimen experienced accelerated carbonation and calcite and vaterite crystals were precipitated in the matrix. e) Accelerated carbonation to cure bio-composite specimens could be used as a way for storing/trapping carbon dioxide in an engineered product. This in addition to serving as a way for sequestering carbon dioxide, enhances the strength of the bio-composite by densifying the microstructure through carbonation. f) The wood-based bio-composite specimens portray strong performance under compression loading. At 56 days, all the specimens meet the minimum requirement of compressive strength of 100 MPa as specified by ASTM C208 for cellulose based insulation panels. g) The wood-based bio-composite specimens are weak in flexure. At 56 days, the mix with the highest flexure strength (60L-35MK-5W) still lacks in meeting the minimum requirement of modulus of rupture 276 kPa as specified by ASTM C208 for cellulose based insulation panels. The low flexural strength of the specimens denotes that the bio-composite might get damaged while handling. Even for non-structural components, poor performance under flexure is a concerning factor since this greatly reduces the handling ability and the subsequent usability of such panels in building components. 79 h) The thermal conductivity of the bio-composite specimens is comparable to the minimum requirement of 0.06 W/mK specified in ASTM C208. The mixes with binders containing 60% lime had thermal conductivity less than 0.054 W/mK while the mixes with binders containing 50% lime had thermal conductivity closer to 0.06 W/mK. The bio-composite produced from waste wood is an innovative and effective way to recycle used and contaminated wood from construction industry. The use of lime-metakaolin based binders with waste wood also helps lower the carbon footprint and increase the service life of wood[27]. 5.2 Recommendations for future work The bio-composite developed in this work performed well and met majority of the criteria deemed important in the performance of an insulation panel. The fundamental findings of this work establish a basic framework to be followed during manufacture, curing, testing and handling of wood based bio-composite. However, it would still be useful to study certain characteristics to improve the overall performance of the product and develop it into a commercially successful material. Some of the recommendations for future work are: a) Reinforcement with fibers The flexural strength of the bio-composite designed in this work was not enough to meet the ASTM standard values. The specimens suffer from poor flexibility due to the rigidity of the wood pieces. Utilising a longer fibrous component in combination with the wood chips would provide the product with higher flexure strength and increased flexibility. Plant derived aggregates like hemp fibers, cotton stalk, and sunflower pith can be used additionally as reinforcements to enhance the strength of bio-composite[13]. 80 b) Treatment of wood As discussed earlier in this work, wood pieces contain several organic substances like hemicellulose, sugar, phenol and carboxylic acids [10]. These organic compounds are known to often interfere with the setting and hardening cementitious materials. Although lime was seen to form a good bonding with the wood pieces, it is advantageous to explore the scope of using treated wood. Aigbomian et al. used sawdust to manufacture wood-crete treated through various methods like boiling and alkali exposure [10]. The same treatment could be applied to wood chips and its effect on the bonding studied. c) Carbon sequestration The employment of carbon dioxide chamber to cure the specimens opens an avenue for sequestration. The use of carbon dioxide to form calcium carbonate offers a viable method for safe and permanent capturing of carbon dioxide. This property could be explored further to find ways to directly capture the carbon emissions from industries. d) Carbonation The process of carbonation is an indispensable part of the manufacturing process of bio-composites in this research work. Curing the specimens at 4% CO2 precipitated enough calcium carbonate to realise the desired strength in the specimen. However, there are studies on amine based resins that improve the carbon capturing ability of the matrix [21], [38], [57]. This technique may be able to enhance the carbonation process and improve the quality of calcite crystals formed. 81 e) Water absorption Since the bio-composite is made from wood, it suffers from excess water absorption. Although it first facilitates the carbonation process, in order to be used in buildings there are coatings that need to be applied to make it impermeable to rain water. There have been studies on hempcrete where the exterior wall surface is made impermeable to water through a cement and lime based coating [58]. Such coating could be applied in case of bio-composites discussed in this research work too. The coatings could be done in such a way that the exterior surface (surface exposed to outdoor climate) could be made impermeable to water and the interior surface (surface exposed to indoor climate) could be made permeable to vapour [58]. This way the hygrothermal properties of the bio-composite can also be put to use in the building. 82 References [1] Pachauri, Rajendra K., Myles R. Allen, Vicente R. Barros, John Broome, Wolfgang Cramer, Renate Christ, John A. Church et al. Climate change 2014: synthesis report. Contribution of Working Groups I, II and III to the fifth assessment report of the Intergovernmental Panel on Climate Change. Ipcc, 2014. [2] M. Zimmermann, H.-J. Althaus, and A. Haas, “Benchmarks for sustainable construction: A contribution to develop a standard,” Energy Build., vol. 37, no. 11, pp. 1147–1157, 2005. [3] O. Ortiz, F. Castells, and G. Sonnemann, “Sustainability in the construction industry: A review of recent developments based on LCA,” Constr. Build. Mater., vol. 23, no. 1, pp. 28–39, 2009. [4] M. Yeheyis, K. Hewage, M. S. Alam, C. Eskicioglu, and R. Sadiq, “An overview of construction and demolition waste management in Canada: A lifecycle analysis approach to sustainability,” Clean Technol. Environ. Policy, vol. 15, no. 1, pp. 81–91, 2013. [5] Metro Vancouver, “DLC Waste Management Toolkit.”BuildSmart.2008. [6] D. N. Saheb and J. P. Jog, “Natural fiber polymer composites: a review,” Adv. Polym. Technol. J. Polym. Process. Inst., vol. 18, no. 4, pp. 351–363, 1999. [7] C. Magniont, G. Escadeillas, M. Coutand, and C. Oms-Multon, “Use of plant aggregates in building ecomaterials,” Eur. J. Environ. Civ. Eng., vol. 16, no. sup1, pp. s17–s33, 2012. [8] D. Dai and M. Fan, “Preparation of bio-composite from wood sawdust and gypsum,” Ind. Crops Prod., vol. 74, pp. 417–424, 2015. [9] E. P. Aigbomian and M. Fan, “Development of Wood-Crete building materials from sawdust and waste paper,” Constr. Build. Mater., vol. 40, pp. 361–366, 2013. [10] E. P. Aigbomian and M. Fan, “Development of wood-crete from treated sawdust,” Constr. 83 Build. Mater., vol. 52, pp. 353–360, 2014. [11] X. Zhou, F. Zheng, H. Li, and C. Lu, “An environment-friendly thermal insulation material from cotton stalk fibers,” Energy Build., vol. 42, no. 7, pp. 1070–1074, 2010. [12] A. D. T. Le, C. Maalouf, T. H. Mai, E. Wurtz, and F. Collet, “Transient hygrothermal behaviour of a hemp concrete building envelope,” Energy Build., vol. 42, no. 10, pp. 1797–1806, 2010. [13] V. Nozahic, S. Amziane, G. Torrent, K. Saïdi, and H. De Baynast, “Design of green concrete made of plant-derived aggregates and a pumice–lime binder,” Cem. Concr. Compos., vol. 34, no. 2, pp. 231–241, 2012. [14] S. Benfratello, C. Capitano, G. Peri, G. Rizzo, G. Scaccianoce, and G. Sorrentino, “Thermal and structural properties of a hemp–lime biocomposite,” Constr. Build. Mater., vol. 48, pp. 745–754, 2013. [15] B. Agoudjil, A. Benchabane, A. Boudenne, L. Ibos, and M. Fois, “Renewable materials to reduce building heat loss: Characterization of date palm wood,” Energy Build., vol. 43, no. 2–3, pp. 491–497, 2011. [16] A. Karmarkar, S. S. Chauhan, J. M. Modak, and M. Chanda, “Mechanical properties of wood–fiber reinforced polypropylene composites: Effect of a novel compatibilizer with isocyanate functional group,” Compos. Part A Appl. Sci. Manuf., vol. 38, no. 2, pp. 227–233, 2007. [17] A. Ashori, “Wood–plastic composites as promising green-composites for automotive industries!,” Bioresour. Technol., vol. 99, no. 11, pp. 4661–4667, 2008. [18] N. M. Stark and R. E. Rowlands, “Effects of wood fiber characteristics on mechanical properties of wood/polypropylene composites,” Wood fiber Sci. Vol. 35, no. 2 Pages 167-84 174, 2003. [19] S. E. Selke and I. Wichman, “Wood fiber/polyolefin composites,” Compos. Part A Appl. Sci. Manuf., vol. 35, no. 3, pp. 321–326, 2004. [20] S.-J. Kim, J.-B. Moon, G.-H. Kim, and C.-S. Ha, “Mechanical properties of polypropylene/natural fiber composites: Comparison of wood fiber and cotton fiber,” Polym. Test., vol. 27, no. 7, pp. 801–806, 2008. [21] L. Wang and D. C. W. Tsang, “Carbon dioxide sequestration on composites based on waste wood,” in Carbon Dioxide Sequestration in Cementitious Construction Materials, Elsevier, 2018, pp. 431–450. [22] A. Ashori, T. Tabarsa, K. Azizi, and R. Mirzabeygi, “Wood–wool cement board using mixture of eucalypt and poplar,” Ind. Crops Prod., vol. 34, no. 1, pp. 1146–1149, 2011. [23] F. Pacheco-Torgal and S. Jalali, “Cementitious building materials reinforced with vegetable fibres: A review,” Constr. Build. Mater., vol. 25, no. 2, pp. 575–581, 2011. [24] R. Eires, J. P. Nunes, R. Fangueiro, S. Jalali, and A. Camões, “New eco-friendly hybrid composite materials for civil construction,” 2006. [25] P. B. de Bruijn, K.-H. Jeppsson, K. Sandin, and C. Nilsson, “Mechanical properties of lime–hemp concrete containing shives and fibres,” Biosyst. Eng., vol. 103, no. 4, pp. 474–479, 2009. [26] T. M. Dinh, C. Magniont, M. Coutand, and G. Escadeillas, “Hemp concrete using innovative pozzolanic binder,” in Proc 1st Int Conf on Bio-Based Build Mater, Ed. Amziane, S., Sonebi, M., Clermont-Ferrand (France), 2015, pp. 21–24. [27] M. Sinka and G. Sahmenko, “Sustainable thermal insulation biocomposites from locally available hemp and lime,” in Environment. Technology. Resources. Proceedings of the 9th 85 International Scientific and Practical Conference, 2013, vol. 1, pp. 73–77. [28] R. M. H. Lawrence, T. J. Mays, P. Walker, and D. D’ayala, “Determination of carbonation profiles in non-hydraulic lime mortars using thermogravimetric analysis,” Thermochim. Acta, vol. 444, no. 2, pp. 179–189, 2006. [29] A. Vimmrova, M. Keppert, O. Michalko, and R. Černý, “Calcined gypsum–lime–metakaolin binders: Design of optimal composition,” Cem. Concr. Compos., vol. 52, pp. 91–96, 2014. [30] R. Černý, A. Kunca, V. Tydlitát, J. Drchalová, and P. Rovnaníková, “Effect of pozzolanic admixtures on mechanical, thermal and hygric properties of lime plasters,” Constr. Build. Mater., vol. 20, no. 10, pp. 849–857, 2006. [31] A. Gameiro et al., “Physical and chemical assessment of lime–metakaolin mortars: Influence of binder: aggregate ratio,” Cem. Concr. Compos., vol. 45, pp. 264–271, 2014. [32] Ö. Cizer, K. Van Balen, and D. Van Gemert, “Competition between hydration and carbonation in hydraulic lime and lime-pozzolana mortars,” in Advanced Materials Research, 2010, vol. 133, pp. 241–246. [33] O. Cizer, K. Van Balen, J. Elsen, and D. Van Gemert, “Crystal Morphology of Precipitated Calcite Crystals From Accelerated Carbonation of Lime Binders,” 2nd Int. Conf. Accel. Carbonation Environ. Mater. Eng. Rome, Italy,1-3 Oct. 2008, no. October, pp. 1–3, 2008. [34] M. Chabannes, E. Garcia-Diaz, L. Clerc, and J.-C. Bénézet, “Studying the hardening and mechanical performances of rice husk and hemp-based building materials cured under natural and accelerated carbonation,” Constr. Build. Mater., vol. 94, pp. 105–115, 2015. [35] A. Almeida, G. H. D. Tonoli, S. F. Santos, and H. Savastano Jr, “Improved durability of vegetable fiber reinforced cement composite subject to accelerated carbonation at early 86 age,” Cem. Concr. Compos., vol. 42, pp. 49–58, 2013. [36] V. D. Pizzol, L. M. Mendes, L. Frezzatti, H. Savastano Jr, and G. H. D. Tonoli, “Effect of accelerated carbonation on the microstructure and physical properties of hybrid fiber-cement composites,” Miner. Eng., vol. 59, pp. 101–106, 2014. [37] L. Wang, S. S. Chen, D. C. W. Tsang, C. S. Poon, and K. Shih, “Value-added recycling of construction waste wood into noise and thermal insulating cement-bonded particleboards,” Constr. Build. Mater., vol. 125, pp. 316–325, 2016. [38] L. Wang, S. S. Chen, D. C. W. Tsang, C.-S. Poon, and K. Shih, “Recycling contaminated wood into eco-friendly particleboard using green cement and carbon dioxide curing,” J. Clean. Prod., vol. 137, pp. 861–870, 2016. [39] L. Wang, S. S. Chen, D. C. W. Tsang, C.-S. Poon, and J.-G. Dai, “CO2 curing and fibre reinforcement for green recycling of contaminated wood into high-performance cement-bonded particleboards,” J. CO2 Util., vol. 18, pp. 107–116, 2017. [40] L. Wang et al., “Upcycling wood waste into fibre-reinforced magnesium phosphate cement particleboards,” Constr. Build. Mater., vol. 159, pp. 54–63, 2018. [41] L. Wang et al., “Transforming wood waste into water-resistant magnesia-phosphate cement particleboard modified by alumina and red mud,” J. Clean. Prod., vol. 168, pp. 452–462, 2017. [42] ASTM International. ASTM C208-12(2017)e1 Standard Specification for Cellulosic Fiber Insulating Board. West Conshohocken, PA; ASTM International, 2017. doi: https://doi.org/10.1520/C0208-12R17E01 [43] S. Elfordy, F. Lucas, F. Tancret, Y. Scudeller, and L. Goudet, “Mechanical and thermal properties of lime and hemp concrete (‘hempcrete’) manufactured by a projection process,” 87 Constr. Build. Mater., vol. 22, no. 10, pp. 2116–2123, 2008. [44] U. Dhakal, U. Berardi, M. Gorgolewski, and R. Richman, “Hygrothermal performance of hempcrete for Ontario (Canada) buildings,” J. Clean. Prod., vol. 142, pp. 3655–3664, 2017. [45] J. Xu, R. Sugawara, R. Widyorini, G. Han, and S. Kawai, “Manufacture and properties of low-density binderless particleboard from kenaf core,” J. Wood Sci., vol. 50, no. 1, pp. 62–67, 2004. [46] N. Y. Zou, “Thermal Insulation Materials for Wall and Roof,” Chem. Ind. Publ. House, 2008. [47] “Dolomitic Hydrated Lime Type S,” Graymont. [Online]. Available: http://www.graymont.com/en/products/hydrated-lime/dolomitic-hydrated-lime-type-s. [Accessed: 19-Aug-2019]. [48] ASTM International. ASTM C141/C141M-14 Standard Specification for Hydrated Hydraulic Lime for Structural Purposes. West Conshohocken, PA; ASTM International, 2014. doi: https://doi.org/10.1520/C0141_C0141M-14 [49] whitemudresources.com. [Online]. Available: http://www.whitemudresources.com/. [Accessed: 19-Aug-2019]. [50] A. Buchwald, H. Hilbig, and C. Kaps, “Alkali-activated metakaolin-slag blends—performance and structure in dependence of their composition,” J. Mater. Sci., vol. 42, no. 9, pp. 3024–3032, 2007. [51] L. Chen, Z. Wang, Y. Wang, and J. Feng, “Preparation and properties of alkali activated metakaolin-based geopolymer,” Materials (Basel)., vol. 9, no. 9, p. 767, 2016. [52] ASTM International. ASTM C109/C109M-16a Standard Test Method for Compressive Strength of Hydraulic Cement Mortars (Using 2-in. or [50-mm] Cube Specimens). West 88 Conshohocken, PA; ASTM International, 2016. doi: https://doi.org/10.1520/C0109_C0109M-16A [53] ASTM International. ASTM C209-15 Standard Test Methods for Cellulosic Fiber Insulating Board. West Conshohocken, PA; ASTM International, 2015. doi: https://doi.org/10.1520/C0209-15 [54] ASTM International. ASTM C165-07(2017) Standard Test Method for Measuring Compressive Properties of Thermal Insulations. West Conshohocken, PA; ASTM International, 2017. doi: https://doi.org/10.1520/C0165-07R17 [55] ASTM International. ASTM C518-17 Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus. West Conshohocken, PA; ASTM International, 2017. doi: https://doi.org/10.1520/C0518-17 [56] E. Vejmelková, M. Keppert, Z. Keršner, P. Rovnaníková, and R. Černý, “Mechanical, fracture-mechanical, hydric, thermal, and durability properties of lime–metakaolin plasters for renovation of historical buildings,” Constr. Build. Mater., vol. 31, pp. 22–28, 2012. [57] C. Gebald, J. A. Wurzbacher, P. Tingaut, T. Zimmermann, and A. Steinfeld, “Amine-based nanofibrillated cellulose as adsorbent for CO2 capture from air,” Environ. Sci. Technol., vol. 45, no. 20, pp. 9101–9108, 2011. [58] A. Piot, T. Béjat, A. Jay, L. Bessette, E. Wurtz, and L. Barnes-Davin, “Study of a hempcrete wall exposed to outdoor climate: Effects of the coating,” Constr. Build. Mater., vol. 139, pp. 540–550, 2017.
Thesis/Dissertation
eng
Civil Engineering
Vancouver : University of British Columbia Library
Attribution-NonCommercial-NoDerivatives 4.0 International
Graduate
Bio-composite panels from recycled wood chips for sustainable building applications
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