Utilization of biochar from unwashed peanut shell in cementitious building materials – Effect on early age properties and environmental benefits

Abstract

Early stage and fresh properties of cementitious materials are critical to ease of placement and durability. This study investigated the potential of biochar, prepared by pyrolysis of locally generated waste peanut shells, to improve workability, hydration, early age strength and shrinkage of cement mortar and cement-fly ash mortar. Experimental observations suggest that addition of biochar slightly reduced workability, reflected in the increase in yield stress and reduction in flow. The biochar used in this study enhanced the degree of hydration by 13–23% and accelerated rate of final setting by 1–1.5 h depending on mix composition. The presence of contaminants including salt and phosphorus in the biochar influences hydration kinetics and setting of cement pastes. The fine particle size of the biochar improved the compactness of cementitious matrix which contributed to increase in early age strength (up to 7 days) of normal and fly ash mortar by 18% and 22%, respectively. The results show that biochar addition can accelerate strength development in fly ash-cement, which is promising for the development of high early-strength concrete with reduced cement demand. However, shrinkage of mortar increased with the dosage of biochar, due to the presence of salts in unwashed peanut shells. Using biochar to replace 3% of cement, can reduce CO2-equivalent emission, attributed to the net sequestration of carbon in the biochar.