Concrete Sulphate Attack in a Sulfate-Free Environment

This paper provides an example of the application of the holistic model to the study of one of the most complex phenomenon in the science of concrete durability, namely the deterioration caused by delayed ettringite formation (DEF) in a sulfate-free environment. By adopting the holistic approach, a new model to explain this damage is proposed. The model is based on three essential elements: late-sulfate release, microcracking, and exposure to water. Late-sulfate release, from a cement with high-sulfate content (especially that with high content of clinker sulfate in less available form) can cause the delayed deposition of ettringite in pre-existing microcracks after sulfate ions diffuse through the pore solution in concrete, either intermittently, or continuously exposed to environmental water. Microcracking may be promoted by alkali-silica reaction, steam curing at high temperatures, localized high stress in prestressed concrete structures or other causes. Theoretically, the DEF-induced damage occurrence can be reduced or prevented by controlling at least one of the above three parameters. In practice, the best way of reducing the DEF-induced damage risk is either to avoid cements with high clinker sulfate that are responsible for the late-sulfate release, or to adopt lower and more homogeneous stress distribution derived from the prestressing process in precast elements, such as concrete ties.