Biochar and recycled gypsum drywall in concrete: role and effects on compressive behavior, microstructure, and carbon footprint.

This research examines the effect of biochar and recycled gypsum drywall (RGD) on the mechanical properties and microstructure of conventional and high-volume fly ash concrete (HVFC) by testing 60 cylinders. Results suggested that although adding biochar increased the porosity of concrete, its effect on concrete's properties relied on its porosity, pore interconnectivity, and water retention capacity, plus characteristics of binders. The biochar-retained water (BRW) accelerated the hydration of C3S, increasing the dosage of calcium carbonate and calcium aluminate silicate hydrate on the top of biochar pores. The accelerated hydration enhanced early-age strength. Besides the hydration acceleration of OPC, BRW primarily promoted the RGD reactions and fly ash activation in HVFC. Nonetheless, the high porosity, inertness, and potential deterioration of biochar weakened the concrete in the long term and lowered its elastic modulus. Biochar also boosted ductile behavior, especially in HVFC with RGD, and lowered the carbon footprint of the concrete. [ABSTRACT FROM AUTHOR]