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

Abstract

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.

The effects of seawater and nanosilica on the performance of blended cements and composites

“…These observations are in line with the work of Demir et al (2010), where only marginal effects of SF incorporation in concrete mixes with seawater were observed. In contrast, Sikora et al (2019b) have recently reported the beneficial effect of combining nanosilica and seawater on the acceleration of hydration processes and the early strength development of OPC systems.…”

“…The solid mass of the NS suspension was 50 wt% and as such, the liquid phase of the suspension was considered as a part the of mixing water in the production of the cement pastes and mortars. The same NS structures have been used in previous studies and have been comprehensively characterized in the work of Sikora et al (2019b). High-resolution transmission electron microscope (TEM) micrographs ( Fig.…”

“…11. Typically, the initial amount of CH in cement paste depends on the type of cement used, with specimens made of pozzolan-and slag-blended cement exhibiting significantly lower amounts of CH content, as compared to plain OPC paste (Sisomphon and Franke 2011;Sikora et al 2019b). It can be seen that in both types of cements, CH content increased gradually until 28 days of curing; this being attributable to the fact that both binders used in this study were low heat cements, in which the cement hydration process is moderate.…”

“…Also, most of the available studies have focused on plain OPC systems. It is widely agreed that seawater has an accelerating effect of cement hydration processes (Govindarajan and Gopalakrishnan 2011;Li et al 2018a;Younis et al 2018;Montanari et al 2019;Sikora et al 2019b) and contributes to a decrease in the setting time and workability of concrete (Etxeberria et al 2016b;Younis et al 2018;Li et al 2019;Teng et al 2019). Early strength improvement, as an effect of accelerated cement hydration, has been widely reported (Demir et al 2010;Wegian 2010;Otsuki et al 2012;Abdel-Magid et al 2016;Etxeberria et al 2016a;Li et al 2018a).…”

“…After 28 days of curing, the effects of seawater in OPC-based concrete are considered to be minor and strength improvements (if at all observable) are generally limited to 5-10%, with long-term mechanical performance being reported as slightly lower than that of OPC-based concrete produced with freshwater (Mbadike and Elinwa 2011;Etxeberria and Gonzalez-Corominas 2018;Guo et al 2018;Bertola et al 2019). Moreover, a refinement in pore structure and an improvement in the permeability of seawater-mixed composites has been reported (Ishikawa et al 2014;Khatibmasjedi et al 2019;Montanari et al 2019;Sikora et al 2019b).…”