Carbonaceous micro-filler for cement: Effect of particle size and dosage of biochar on fresh and hardened properties of cement mortar.

This study explores influence of biochar particle size and surface morphology on rheology, strength development and permeability of cement mortar, under moist and dry curing condition. Experimental results show that the flowability and viscosity of cement paste is more affected by macro-porous coarser (or 'normal') biochar particles of size 2-100 μm (NBC) compared to fine (or 'ground' biochar), which is in the size range of 0.10-2 μm (GBC). Addition of both GBC and NBC accelerated hydration kinetics and improved early (1-day) and 28-day strength by 20-25% compared to the control. Water permeability, measured by capillary absorption was reduced by about 50% compared to control mortar, due to the addition of 0.50-1% NBC and GBC respectively. GBC is found to be more effective in minimizing loss in strength and water tightness under dry curing condition compared to the control and mortar with NBC and quartz filler respectively. In summary, findings from the study show that finer biochar particles offer superior performance in improving early strength and water tightness compared to normal biochar (with macro-pores), while 28-day properties are similar for mortar with both GBC and NBC respectively.