Mechanism of strength evolution of seawater OPC pastes

This work investigated the strength degradation mechanisms of seawater ordinary Portland cement (OPC) pastes. Two types of specimens were prepared ((i) OSD sample (i.e. OPC was mixed with seawater, and then cured in deionized (DI) water) and (ii) ODD sample (i.e. OPC was mixed with DI water, and then cured in DI water, as the reference system)). The use of seawater in preparing OPC pastes effectively increased the hydration rate and early-age mechanical strength, but lowered the mechanical strength at the later age. The higher hydration degree and larger amounts of carbonates with a smaller crystal size enabled the seawater OPC pastes to exhibit a higher early-age mechanical strength, increasing by 13.0%–17.0% compared with the DI water OPC pastes. While the formation of Friedel’s salt and the formation of calcium-silicate-hydrate (C-S-H) gel with a lower polymerization degree and mean molecular chain length resulted in the deterioration of the pore structure and negatively affected the later-age strength development of the seawater OPC paste, decreasing by 5.8%–11.9% compared with the DI water OPC pastes.