Comparative study on the effect of agricultural waste biochar on the properties of cement mortar

Biochar is an organic material prepared by anaerobic pyrolysis and is extensively used in the building materials industry for its excellent carbon sequestration performance. This study used biochar prepared by pyrolysis of agricultural wastes (peanut shells, corncob and wood chips) to prepare biochar mortar by replacing cement in different proportions (1.0 %, 3.0 % and 5.0 %). The workability, mechanical strength, shrinkage properties, phase composition and microstructure of biochar cement mortar have been systematically studied. The results show that the fluidity of the cement mortar decreases significantly with increasing biochar substitution rate, which is on the order of that of peanut shell biochar, corncob biochar, and wood biochar. The mechanical strength of the cement mortar increases and then decreases with the biochar substitution rate, reaching optimality at 3.0 %. Among them, peanut shell biochar mortar had the best mechanical properties, and its 28d flexural and compressive strengths were higher than those of ordinary cement mortar by 6.6 % and 8.8 %, respectively. Moreover, the shrinkage of cement-based materials progressively decreases as the biochar substitution rate increases, and the 28 d shrinkage rate of peanut shell biochar mortar was 25.3 % lower than that of ordinary mortar. The results of microscopic analysis showed that the main mineral components of cement-based materials prepared by biochar were Ca(OH) 2 , CaCO 3 , ettringite and C-S-H gel. Peanut shell biochar exhibits excellent carbon sequestration properties. Cement mortar with 3.0 % peanut shell biochar reduced CO 2 emissions by 19.0 % compared to regular cement mortar. • Agricultural waste biochar has the potential to prepare green building materials. • Cement mortar with 3.0 % peanut shell biochar content exhibits optimal basic performance. • The CO 2 emission of peanut shell biochar mortar is 19.0 % lower than that of ordinary cement mortar.