New frontiers in sustainable cements: Improving the performance of carbonated reactive MgO concrete via microbial carbonation process

The low conversion of reactive MgO cement (RMC) into hydrated magnesium hydroxy carbonates (HMHCs) due to limited CO₂ diffusion towards the sample core leads to inefficient RMC use and low strength development in RMC concrete. This study proposed a novel technique to enhance hydration and carbonation at both the exterior and core sections of RMC concrete via a synergistic combination of microbial carbonation process (MCP) with nucleation seeding (S). The production of CO₃²⁻ ions via the introduction of urease-producing bacteria to catalyze the hydrolysis of urea enabled self-carbonation of RMC, leading to the formation of HMHCs under ambient conditions. Improvements in CO₂ dissolution and formation of brucite with a low crystallinity further stimulated HMHC formation under accelerated carbonation conditions. The simultaneous use of MCP and S resulted in dense microstructures composed of HMHCs with improved morphologies, translating into strengths that were >3 times of the control (62 vs 20 MPa).