SULFATE ATTACK ON CONCRETE

The types of disruption observed during sulphate attack on mortars or concretes, and the chemical processes involved, are summarized. Concrete mix design and binder type have an important influence on concrete performance in sulphate environments. The present UK Codes of Practice (based on BRE Digest 250) reflect the technical information available for various binders currently used in the UK. Sulphate-resisting Portland cement is a purpose-made cement designed to resist sulphates. The chemical factors giving rise to its sulphate resistance are well understood, and its performance has been uniformly good in experimental trials throughout the world. This cement is the standard by which other binders are judged, and should continue to be the preferred binder for concretes expected to withstand sulphate concentrations in ground waters greater than 3000 mg SO4--/l. Although partial replacement of ordinary Portland cement (OPC) by various latent hydraulic binders can lead to improved sulphate resistance, the mechanism by which these latent hydraulic binders act is not established. There is well-documented evidence of considerable variability of performance for OPC/pulverized fuel ash and OPC/ground granulated blastfurnace slag combinations, and the ability of composite cements to provide a guaranteed performance is suspect. A more rigorous approach towards the selection of composite binder components in the appropriate standards is required before their use can be recommended in ground waters where sulphate levels exceed 3000 mg SO4--/l.