Effect of Sea Water on the Strength and Durability of Cement Concrete

Effect of Sea Water on the Strength and Durability of Cement Concrete
1 Introduction
The use of seawater in concrete production has emerged as a critical area of investigation, driven by the escalating global water crisis and the need for sustainable construction practices in coastal regions. Freshwater scarcity affects approximately 2.2 billion people worldwide, and the concrete industry consumes about 9% of total global industrial water usage . In coastal and island areas where freshwater is limited or must be transported over long distances at considerable cost and energy expenditure, seawater presents a practical alternative for concrete mixing and curing .
The historical precedent for seawater concrete dates back to the Romans, who built concrete structures along the Mediterranean coastline using seawater . Modern interest in this practice has intensified in recent decades, with research focusing on both the potential benefits and the significant durability challenges associated with chloride and sulfate ions present in seawater. Understanding the effects of seawater on the strength and durability of cement concrete is essential for determining appropriate applications and developing mitigation strategies.
2 Composition of Seawater and Mechanisms of Interaction
Seawater typically has a salinity of approximately 3.5%, containing dissolved ions including chloride (Cl⁻), sodium (Na⁺), magnesium (Mg²⁺), sulfur (S²⁻), calcium (Ca²⁺), and potassium (K⁺) . These ions interact with cement hydration products in complex ways that influence both fresh and hardened concrete properties.
2.1 Acceleration of Hydration
Chloride ions in seawater are known to accelerate cement hydration. The mechanism involves a chemical reaction between sodium chloride and calcium hydroxide produced during hydration, resulting in the formation of calcium chloride (CaCl₂), a powerful accelerator . This acceleration effect is manifested in reduced setting times—seawater concrete exhibits initial setting times approximately 25% faster than freshwater concrete (33 minutes versus 42 minutes in one study) .
2.2 Formation of Additional Phases
The interaction of seawater ions with hydration products leads to the formation of additional phases not typically present in freshwater concrete. Friedel's salt (calcium chloroaluminate hydrate) forms through the reaction of chloride with AFm phases, while ettringite and gypsum form through reactions involving sulfate ions . A comparative study of brine-seawater sand concrete and ordinary concrete revealed that seawater-mixed systems had larger mass fractions of amorphous phase (primarily C-S-H), ettringite, and gypsum during hydration . These phase formations influence the microstructure and, consequently, the physical and mechanical properties of concrete.
2.3 Chloride Binding
Seawater-mixed cementitious systems exhibit a unique characteristic: chloride binding occurs during early hydration (within 48 hours) through interaction with C₃S and C₃A phases . This early chloride binding capacity can mitigate corrosion risk by reducing the concentration of free chlorides available to initiate steel depassivation. However, the stability of bound chlorides is a concern, as chemical binding can be partially or completely undone, and physical binding can be lost with carbonation of hydrated cement phases .
3 Effect on Strength
3.1 Early-Age Strength
The most consistently observed effect of seawater on concrete strength is enhanced early-age strength development. Studies demonstrate that seawater concrete achieves significantly higher compressive strength at 7 days compared to freshwater concrete . This improvement is attributed to the acceleration of hydration by chloride ions, which promotes more rapid formation of C-S-H gel and refinement of pore structure at early ages . The accelerated setting and strength gain can be advantageous in construction schedules where rapid formwork turnover is desired.

    Date: 2026-09-18 00:00:00.000000