Optimizing Biocarbonation of Reactive Magnesia Cement for Enhanced Strength and Durability in Sandy Soil Reinforcement

Biocarbonation of reactive magnesia cement (RMC) is an innovative and potentially sustainable technique for soil improvement. This study aims to optimize the ratios of key parameters: microbial dosage (10%–30%), RMC content (3%–10%), and urea content (0–4 mol/L). On this basis, the long-term performance was evaluated through dry-wet cycle tests. Experimental results indicated that a linear relationship existed between microbial dosage and RMC content. The optimal urea concentration was determined to be 1 mol/L. Moreover, the unconfined compressive strength (UCS) increased with the augmentation of RMC content, reaching up to 4.2 MPa, which was 142.77%–250% higher than that of PC (Portland cement) and MICP (Microbial induced carbonate precipitation) samples. Additionally, the mass and strength losses of the sample with 8% RMC content after 8 dry-wet cycles were only 0.62% and 5.58%, respectively- reduced by up to 70% compared with PC and MICP samples. The micro-tests results showed that the strength of the samples can be attributed to the synergistic effect of hydrated magnesia carbonates (HMCs) and Mg(OH)2. During the dry-wet cycle, the residual RMC in the sample would continue to hydrate and fill the pores. The obtained findings have demonstrated that the biocarbonation of RMC has engineering feasibility.