IN-SITU STABILIZATION OF CACO3 POLYMORPHS IN CEMENTITIOUS SYSTEMS

The technology of injecting CO2 in a cementitious system (concrete) during mixing has demonstrated scalability and significant potential. This process involves CO2 dissolving in water, releasing carbonate and bicarbonate ions that react with calcium ions from dissolving clinker and hydrate phases, leading to in-situ CaCO3 precipitation. This study examines CaCO3 formation pathways and explores stabilizing favourable polymorphs using additives. Cement paste samples were analyzed using FTIR and X-ray diffraction. Initial results suggest CaCO3 formation follows Ostwald's process. In early hydration (up to 6 hours), amorphous calcium carbonate and metastable crystalline polymorphs (vaterite and aragonite) form. These metastable forms then crystallize into calcite, the most stable polymorph, observed at 24 hours and beyond. Various amino acids (e.g., L-Arginine, L-Aspartic acid) are being tested to stabilize metastable polymorphs. Preliminary findings indicate these acids can successfully stabilize metastable polymorphs in-situ within CO2-injected cementitious systems.