Carbonation reactivity enhancement of γ-C2S through biomineralization

Most of the calcium silicates exhibit high carbonation reactivity, and thus start to be utilized in the production of low carbon concrete due to the growing pressure of carbon mitigation in the cement industry. In this study, powdered gamma-C2S, with limited hydraulicity, is preconditioned in a suspension consisting of urease-producing bacterium and urea. This biomineralization process induces the precipitation on the gamma-C2S surface of calcite crystals with spherical shape, the size of which is dependent on the urea suspension concentration. The effect of the pre-existing calcite crystals on the carbonation behavior, mechanical and micro-morphology of gamma-C2S compacts is investigated. Results indicate the compressive strength are significantly improved with the preexisting calcite crystals, and the increasing percentage is 43.66 % at 30 min carbonation and 0.25 mol/L urea concentration. The strength enhancement is found to be associated with the pre-existing calcite crystals acting as nucleation seeds which accelerate the carbonation at the early stage. In addition, the pre-existing calcite seeds induce the preferential formation of calcite in the crystalline carbonation products of gamma-C2S, which may be beneficial to the enhancement of the carbonated products.