Durability of concrete exposed to leaching and external sulphate attacks

Leaching and external sulphate attack on concrete lead to dissolution of hydration products, mainly portlandite, and in case of ingress of sulphate ions to formation of expansive products such as gypsum and ettringite. Durability of concrete exposed to these environments is still based on prescriptive specifications. The aim of the study is to provide experimental data to design performance based tests and specifications for a comparative approach. Tests have been developed to study these degradations in controlled conditions at constant pH. A leaching test has been performed on concrete. Indicators can be deduced from the leaching test and they are sensitive to the variations of potential durability. An accelerated test using a high sulphate concentration has been performed on mortars. Expansion results are sensitive to mortar mix proportions and the test could be used to qualify cements or binders in a comparative approach. Concrete specimens are exposed to external sulphate attack at two levels of sulphate concentration to provide long-term data that can be used to study the relevance of the accelerated tests and models which are being developed. Results from both series of tests show a correlation between the resistance to leaching and the resistance to external sulphate attack.