Utilizing ground biochar desorption for carbon sequestration and internal curing in a clinker-free CaO-activated GGBFS binder

Abstract

This study examines the incorporation of pre-wetted, ground biochar into a clinker-free CaOactivated GGBFS system, highlighting its multi-stage desorption behavior and internal curing benefits. The biochar rapidly released pore-stored water between 1 and 6 h and maintains moisture beyond 6 h, delaying early hydration by up to 8 h but supplying secondary water that reverses initial strength deficits. At dosages up to 3 wt %, 28-day compressive strength did not decrease but was instead improved by approximately 2 % via this internal curing mechanism. However, a 5 wt % replacement caused a 5 % reduction in strength. The primary hydration products-ettringite, C-S-A-H, Ca(OH)2, and hydrotalcite-remained largely unchanged. The biochar incorporation reduced overall pore volume while keeping pore sizes below 50 nm, and enhanced Ca and Si dissolution of GGBFS. The incorporation of biochar and the proposed cementless binder significantly enhanced carbon sequestration, reducing net CO2 emissions to as low as 29.0 kg CO2 per ton of binder, compared to 637.1 kg for Ordinary Portland Cement (OPC)based binder. Furthermore, the emission-to-strength ratio was reduced from 12.74 to 0.96 kg CO2 per MPa. These results underscore biochar's dual role as an effective internal curing agent and carbon-sequestration additive in sustainable clinker-free binders.