Effects of biochar on the shrinkage and mechanical properties of sustainable engineered geopolymer composites: A comparative study between biochar sources, pyrolysis temperatures, and particle sizes

The effects of biochar prepared from different sources, pyrolysis temperatures, and particle sizes on the engineered geopolymer composites have not been well investigated. This paper presented the laboratory investigation of the autogenous shrinkage, compressive and flexural strengths, and tensile performance of sustainable and low-carbon engineered geopolymer composites modified with biochar produced from wood, bamboo, and coconut shell under high (650 °C) and low pyrolysis temperatures (450 °C). The prepared biochar was screened by 300 (coarse) and 75 μm (fine) sieves to obtain different particle sizes. The results indicate that the incorporation of 4 % biochar inhibits the development of the autogenous shrinkage of the engineered geopolymer composites by up to 12.1 %. The autogenous shrinkage decreases with the increased pyrolysis temperature or decreased particle size. The coconut shell biochar is more effective in the shrinkage mitigation than the bamboo or wood biochar. The addition of an appropriate quantity of biochar enhances the compressive, flexural, and tensile strengths of the engineered geopolymer composites, which are increased to 101.7, 14.8 MPa, and 6.62 MPa, with corresponding improvements of 24.2 %, 16.4 %, and 15.0 %, respectively. The tensile strain is improved from 8.83 % to 9.54 %. The cost-benefit analysis indicates that the output of the compressive, flexural, and tensile strengths from the unit cost is increased by up to 24.0 %, 16.2 %, and 14.8 %, respectively. The carbon footprint of the materials used in each mix proportion suggests the compressive, flexural, and tensile strength gain from unit carbon emission is improved by 32.4 %, 27.4 %, and 24.9 %, respectively. The source, pyrolysis temperature, particle size, and dosage to achieve the highest mechanical properties of EGC in this study are coconut shell, 650 °C, smaller than 75 μm, and 2 %, respectively.