Development of sustainable concrete incorporating seawater: A critical review on cement hydration, microstructure and mechanical strength

Many countries are experiencing freshwater crises due to the increasing growth of the population together with the infrastructure construction that is aligned with the needs of freshwater for concrete production. There are also deficiencies in freshwater in many coastal areas where seawater is more accessible. To reduce unnecessary resource-wasting and meanwhile drive sustainable development in the construction industry, great efforts have been made to utilize seawater as the alternative mixing water for concrete casting, which presents potential economical and environmental benefits in the coastal and island regions. This paper comprehensively reviews the current studies on the predominant performance differences between seawater-mixed and conventional concretes with freshwater. Particular attention is paid to the chloride-induced hydration mechanism due to the chloride ions in seawater. The main findings of this review reveal that although harmful ingredients in seawater may weaken some of the concrete performances, applying proper curing conditions and adding moderate additives and admixtures could significantly and effectively mitigate these defects in properties. However, the unstable chloride binding ability in cement hydrates cannot eliminate the risk of rebar corrosion caused by chlorides in seawater, resulting in a limited scope of practical application. Finally, some trade-offs are recommended in using seawater in concrete, suggesting prospects of applications in the future construction industry. This study guides for the safer use of seawater in sustainable concrete through reviewing the advanced research progress