Utilizing bamboo biochar in cement mortar as a bio-modifier to improve the compressive strength and crack-resistance fracture ability

Concrete is an obvious source of global carbon dioxide emissions. In recent years, many kinds of pulverized biochar materials have been used in cement composites to improve the carbon capture ability as well as to enhance the mechanical properties. In this study, bamboo biochar is used to replace some cement to make biochar mortar, in order to improve the compressive strength and crack-resistance ability. By the measurement of the main oxidation chemicals of bamboo biochar, it is found that bamboo biochar meets the requirements of class N – pozzolan and has pozzolanic reaction ability. Thus, it can be used as a useful admixture to mortar. The compressive strength of biochar mortar is higher than that of the control mortar without bamboo biochar, due to the filling and self-curing effects of bamboo biochar. The logarithmic formula and negative exponential formula are used to describe the age strength relationship of biochar mortar at early period. Then the initial and final compressive strength are introduced to illustrate the influence of biochar dosage on the compressive strength of mortar during different age. On another hand, biochar mortar has larger initial cracking fracture toughness and unstable fracture toughness than the control mortar, indicating that bamboo biochar is beneficial for mortar to resist crack initiation and propagation, although it decreases the critical crack length. Considering the compressive strength and fracture toughness, 1–3 wt% replacement of bamboo biochar to cement is suggested as the optimal dosage for mortar in this study.