Multiscale investigations on hydration mechanisms in seawater OPC paste

The freshwater consumption in concrete production has been notably increased, owing to the worldwide demand from the construction sector for the industrial and urban developments. To meet the requirements in the long term, reconsidering the seawater usage in concrete production, as an alternative to freshwater, perhaps can be a sustainable solution. Doing that, the freshwater resource can be effectively preserved, also the durability issues of concrete materials and structures based on marine resources and towards the marine applications can probably be revisited and resolved from new perspectives. At present, most studies about seawater usage in concrete have been conducted using the simulated seawater. It is currently rare to see the systematic and in-depth hydration studies employing directly the real seawater. This research aims at new findings by conducting multiscale investigations on hydration mechanisms of ordinary Portland cement (OPC) with seawater mixing. The investigations were conducted through a combination of macro-, micro- and nano-scale analyses and material characterizations. Seawater enhances the hydration of cement expressed by the accelerated heat flow and increased heat of hydration. Hydrated C-S-H matrix phases with seawater mixing develops with more enriched hydrates and finer microstructure. Compressive strength of the hardened cement paste can increase by 50% when using seawater as the mixing water. Seawater cement paste demonstrates a highly stiffened structure for its rheological behavior at the fresh stage, and it develops a clearly reduced autogenous shrinkage compared to the deionized water cement paste. Formation of Friedel's salt encourages the future studies on chemistry between seawater and cements to beneficially utilize the seawater ingredients to improve the material properties and structural durability.