Portland cement, a fundamental building material, comprises several key components: tricalcium silicate, dicalcium silicate, tricalcium aluminate, and tetracalcium aluminoferrite. Notably, sulphate-resisting cement contains a reduced amount of tricalcium aluminate to mitigate sulphate attack. This is crucial because tricalcium aluminate, in the presence of sulphates, forms calcium sulphoaluminate and gypsum, leading to expansion and cracking within the concrete structure.
However, in marine environments, the use of sulphate-resisting cement is counterintuitive. This is due to tricalcium aluminate’s high affinity for chloride ions, a prevalent component of seawater. As P. Kumar Mehta (1991) suggested, chloride ions can react with tricalcium aluminate to form calcium chloroaluminate hydrate. This reaction depletes the available tricalcium aluminate, which would otherwise help to bind and immobilize harmful chloride ions. The reduced binding capacity can accelerate chloride penetration into the concrete, hastening the corrosion of steel reinforcement and jeopardizing the marine structure’s integrity.
Therefore, while sulphate-resisting cement is beneficial in environments with high sulphate concentrations, it is not suitable for marine applications. In marine environments, a cement with higher tricalcium aluminate content is preferred, as it can better resist chloride attack and protect the embedded steel reinforcement from corrosion. This nuanced understanding of cement chemistry is vital for selecting the appropriate cement type for specific environmental conditions, ensuring the longevity and durability of concrete structures.