Change in crystal polymorphism of CaCO3 generated in cementitious material under various pH conditions

Although concrete is the most universal material in construction, its tensile strength is markedly lower than its compressive strength, resulting in the unavoidable occurrence of cracks in concrete structure. Since infiltration of harmful substances such as chloride, carbon dioxide, and sulfate can occur easily through such cracks, they grow larger and deeper due to repeated infiltration and the concrete structure can eventually suffer catastrophic damage. When the crack widths are small in an aqueous environment, self-healing can occur where a part of the crack is filled by rehydration of the cement particles and precipitation of CaCO3. In addition, self-healing performance can be maximized through control of the crystal forms of CaCO3 by adjusting temperature and pH. Therefore, in this study, the crystal forms of CaCO3 generated in the self-healing process were examined, and changes in the crystal forms of CaCO3 generated in the hardened cement paste through pH adjustment were monitored for the generation of denser CaCO3 crystals. Based on this, the pH conditions enabling the generation of the denser vaterite CaCO3 are presented herein.