The effects of seawater on the hydration, microstructure and strength development of Portland cement pastes incorporating colloidal silica

This contribution investigates the effects of seawater and colloidal silica (NS) in the amounts of 1, 3 and 5 wt%, respectively, on the hydration, strength development and microstructural properties of Portland cement pastes. The data reveal that seawater has an accelerating effect on cement hydration and thus a significant contribution to early strength development was observed. The beneficial effect of seawater was reflected in an improvement in compressive strength for up to 14 days of hydration, while in the 28 days compressive strength values were comparable to that of cement pastes produced with demineralized water. The combination of seawater and NS significantly promotes cement hydration kinetics due to a synergistic effect, resulting in higher calcium hydroxide (CH) production. NS can thus react with the available CH through the pozzolanic reaction and produce more calcium silicate hydrate (C-S-H) gel. A noticeable improvement of strength development, as the result of the synergistic effect of NS and seawater, was therefore observed. In addition, mercury intrusion porosimetry (MIP) tests confirmed significant improvements in microstructure when NS and seawater were combined, resulting in the production of a more compact and dense hardened paste structure. The optimal amount of NS to be mixed with seawater, was found to be 3 wt% of cement.