Mechanism of strength evolution of seawater OPC pastes

Abstract

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.

Physicochemical investigation of Portland cement pastes prepared and cured with seawater

“…Comparing the use of seawater as only the mixing water [6,14,44] with using seawater as both mixing and curing water, MH, as a new hydration product, was obviously formed with a lamellar morphology on the surface of the paste where its particle size was larger compared to that formed in the cured seawater. Furthermore, the CH contents in the outer region of the paste were also significantly lower while MH was formed.…”

Impact of MgCl2 on the mechanical properties of alite pastes at mesoscale and nanoscale

“…10,[12][13][14][15] Most studies agreed that seawater concrete attains higher early strength than freshwater concrete. 10,[16][17][18] Moreover, incorporating seawater would cause the morphology change of hydration products. The main morphological change observed was in the C−S−H structure.…”

“…Significant progress has been made in recent years in the study of seawater concrete, with research focusing on cement hydration, 10–15 microstructure 10,12–15 and mechanical strength 10,12–15 . Most studies agreed that seawater concrete attains higher early strength than freshwater concrete 10,16–18 . Moreover, incorporating seawater would cause the morphology change of hydration products.…”