Crystallization of C-S-H and C-A-S-H in artificial seawater at ambient temperature

Calcium silicate hydrate (C-S-H) or calcium aluminum silicate hydrate (C-A-S-H) are the primary binding phases of Portland and blended cementitious systems. This study investigated the effect of seawater on the crystallization of C-S-H and C-A-S-H with different Al dosages and pH conditions up to 90 days of curing using different experimental techniques. The results showed that the gel phases converted to the crystalline phase, which is known as tobermorite, after 56 days of exposure to seawater under ambient temperature and pressure. It was also observed that relatively low pH (8.2– 10) and Al content within a specific range aided the crystallization of the tobermorite from the gel phase. However, at a high dosage of Al, katoite was observed to precipitate instead of tobermorite. The hydrothermally synthesized tobermorite in different pH conditions and Al-contents also confirmed the role of pH and Al on the crystallization of this phase.