Properties of cement mortar containing pulverized biochar pyrolyzed at different temperatures

Abstract

Cement manufacturing is a significant source of global carbon dioxide emissions, which can be curtailed if a portion of cement is replaced by biochar (BC). Although there are positive outcomes of application in BC-cement composites, the effects of pulverized BC pyrolyzed at different temperatures on the properties of cement mortar is remain unknown. Here we studied the fluidity, setting time, water absorption, mechanical strength, albedo, and thermal conductivity of four types of mortar samples that were mixed with a portion of cement replaced by pulverized BC pyrolyzed at 400 °C, 500 °C, 600 °C, and 700 °C, respectively. The replacement ratio of BC to cement, in weight, was set as 0%, 1%, 3%, 5%, and 10%, respectively. The results suggested that 1–3% was the optimal BC addition (irrespective of its pyrolysis temperature) to improve the strength of the mortar without compromising the other mechanical properties of BC-contained mortar composites. Addition of 1.0% of BC under 400 °C minimized the fluidity and the water absorption by 3.0% and 9.0%, respectively. Besides, both the albedo and thermal conductivity of mortars containing BC pyrolyzed at different temperatures decreased linearly with the rise of BC contents. These new findings offer a new win-win outlet for locking BC in inert cementitious materials and reducing the cement consumption.