A microbial mineralization-based strategy for activating low-carbon recycled concrete powder: mechanical properties and hydration behavior

Recycled concrete powder (RCP) exhibits low activity as a cementitious admixture, and conventional modification techniques struggle to balance environmental friendliness with mild reaction conditions. In this study, microbial mineralization was employed to in situ deposit biogenic calcium carbonate on the RCP surface, thereby enhancing its reactivity. The results show that at dosages of 10%–20%, the mineralized RCP (BRCP) increases the 7d compressive strength of cement paste by 18.2%–20.4% and optimizes the pore size distribution of the paste. Microbial action accelerates the decalcification and dissolution of hydration products in RCP, and the resulting mineralized products serve as nucleation sites for hydration. However, the lower Ca2+ availability and higher surface potential of BRCP delay early hydration, with a more pronounced inhibitory effect at higher replacement ratios. Considering the tradeoff between early inhibition and nucleation enhancement, 15% is identified as the optimal BRCP dosage. This study provides a valuable reference for the low-carbon, high-value utilization of construction waste-derived RCP in green concrete.