Effect of Seawater on Cement Hydration: Experimental Observations and Atomistic Insights

As freshwater scarcity has been challenging for many countries, finding alternative water sources for concrete production is essential for sustainable concrete practices. The use of seawater as mixing or curing water for concrete production is one of the alternative solutions. Although seawater utilization raises durability concerns in reinforced concrete due to chloride and sulfate ions, it remains a promising option for plain concrete applications and for concrete systems incorporating corrosion-resistant reinforcement. This study investigates the effects of seawater on cement hydration through a combined experimental and molecular simulation approach. The experimental program included heat of hydration measurements, compressive strength testing at various curing ages, and microstructural characterization using scanning electron microscopy and X-ray diffraction. The results showed that seawater enhanced the 7-day compressive strength by up to 17.9%, although freshwater-cured specimens exhibited superior 28-day performance. Molecular dynamics simulations were conducted to gain atomistic insights beyond macroscopic observations. Two atomistic models representing cement systems mixed with freshwater and seawater were developed based on major cement clinker phases and dominant seawater ions (Cl⁻ and SO₄²⁻). The seawater model exhibited approximately 15%, 2%, and 4% higher bulk, shear, and Young’s moduli, respectively, than the freshwater model. These findings were further illustrated through molecular snapshots highlighting the distinct local environments around each ion. Overall, the models offer a promising tool for predicting the effects of seawater on cement performance and for designing materials with improved durability in marine conditions.