Rheological properties, compressive strength, hydration products and microstructure of seawater-mixed cement pastes

Abstract

The application of seawater as the mixing water in concrete production could mitigate the increasing demand for fresh water in concrete production associated with the continuously increasing offshore infrastructures. Understanding the key factors that influence the properties of seawater-mixed cementitious materials could promote the application of seawater during concrete preparation. A comprehensive investigation was carried out to assess the effects of the water/cement ratio (w/c), the partial replacement of ordinary Portland cement (OPC) with supplementary cementitious materials, and the salt concentration in seawater on the rheological properties (plastic viscosity (η), dynamic yield stress (τd), thixotropic area (Athix)), compressive strength (fc), hydration products and microstructure of cement pastes. The results show that there was an increase in η, τd, Athix and fc in all seawater mixes compared to deionized (DI) water mixes, and the increase in strength was more significant in the pastes with a lower w/c. The increase in salt concentration in the seawater did not linearly increase fc; instead, the early age strength increased initially and then decreased. This result was due to the combined effects of the increased chloride and Na+ ions on the strength development with the increase in salt concentration in the seawater. Interestingly, it was found that there was a good correlation between the results of η and fc for the seawater mixes in this study, and the same η value indicated a higher fc in the seawater mix than in the DI water mix.