A novel bio-carbonation method of reactive magnesia with urea pre-hydrolysis for geomaterial stabilisation

This study proposes a novel bio-carbonation method of reactive magnesia cement (RMC) with urea pre-hydrolysis for geomaterial stabilisation. Urea pre-hydrolysis in the bacterial solution before mixing with RMC produces more carbonate and ammonia, facilitating the RMC bio-carbonation to form more hydrated magnesia carbonates (HMCs), the dominant product that contributes to strength gain. The effect of urea pre-hydrolysis on the engineering performance of bio-carbonated samples is investigated through a series of RMC bio-carbonation geomaterial stabilisation tests with various pre-hydrolysis times and urea concentrations. The results show that the proposed method can improve material utilisation, enhance the RMC bio-carbonation reaction and promote geomaterial stabilisation performance. The relationships between the unconfined compressive strength (UCS) of bio-carbonated samples and the amount of HMCs are studied using a proposed indicator, the degree of carbonation (DC). However, the strength increment is not monotonically related to the amount of HMCs. The optimal pre-hydrolysis time is 6–12 h for bio-carbonated samples with UCS up to 3·79 MPa, and the maximum UCS increase in the samples is up to 404·42%. The critical DC values are in the range 0·23–0·36 with varying urea concentrations. The proposed method has implications for the design of bio-carbonated RMC in field applications.