The effects of apricot kernel shell nanobiochar on mechanical properties of cement composites

Valorization of agricultural wastes is important both economically and environmentally. This study aimed to investigate the use of biochar as a filler to improve the mechanical properties of mortar and to help sequestrate CO2. The biochar was produced by pyrolysis of apricot kernel shell at 500 °C. Nanobiochar particles with dimensions less than 500 nm were obtained by high-energy ball milling process. Scanning electron microscope was used for determining the morphology of nanobiochar. The nanobiochar at different volume percentages [0.00-0.04-0.06-0.08-0.12-0.15%] was added to mortar. The mortar was casted into 40x40x160 mm molds. After water curing at 20°C for 28 days, compressive strength and flexural strength tests were performed. The mixture containing 0.04% nanobiochar by volume had an increase in flexural and compressive strengths by 5% and 15% respectively, while its fracture energies for flexure and compression increased by 98% and 38% respectively compared to the reference mortar. Furthermore, the mixture having 0.12% volume had an increase in flexural and compressive strengths by 32% and 11%, respectively, while the increase in fracture energies for flexure and compression was 52% and 25%, respectively, compared to the reference mortar. The mechanisms of nanobiochar effect on flow, strength, and fracture energy were enlightened. The nanobiochars bridge the cracks, divert the cracks, act as hydration nucleation sites, enhance the matrix by its porous structure, and developed internal curing that led to increase in strength and fracture energy. This study suggests that the biochar produced from the apricot kernel shell has the potential to be used as a carbon sequestering mixture to improve performance of mortar and thereby utilizing waste as a construction material, contributing to the economy and environment.