Roles of wood waste biochar for chloride immobilization in GGBS-blended cement composites

Due to its environmentally friendly features and economic benefits, biochar has garnered increasing attention as a sustainable and carbon-negative material in the construction sector. This study investigated the roles of wood waste biochar in enhancing the chloride immobilization capacity (CIC) of GGBS-blended cement (PG) composites by assessing the chemical chloride immobilization, physical chloride immobilization, and chloride migration resistance. The results indicated an initial increase in the chloride immobilization ratio (CIR) of PG composites, followed by a decrease upon the further increase in biochar dosage. The highest CIR was achieved by PGBC2, containing 2.0 wt% biochar. Microscale characterization revealed that biochar addition increased the formation of Friedel's salts, thereby augmenting chemical chloride immobilization in the PG composites. Furthermore, biochar addition enhanced the adsorption of calcium ions and provided nucleation sites that supported the continuous hydration reaction, forming more hydration products and reinforcing the physical chloride immobilization. The highest compressive strength and elastic modulus were aligned with the lowest water adsorption and total porosity among all the tested groups, supporting the increased resistance of chloride migration in the PGBC composites. These findings offer novel insights into leveraging wood waste biochar for fortifying the durability of GGBS-blended concrete structures in chloride-rich environments.