Sulfate Attack on Concrete: Is it real or just a misinterpretation of damage done by biodeterioration?

Abstract

At the present time, no material is known that is completely inert to chemical or biochemical action and immune to weathering damage. Concrete is no exception, but, under what might be considered normal exposure conditions, it has a very long life. Concrete made by the Romans from natural cement is in excellent condition after more than 2000 years of service. The controversies generated by contradictory expert testimonies in several lawsuits involving sulfate attack on concrete, and by the large numbers of recently published papers containing data on the subject, have caused considerable anxiety about sulfate attack mechanisms and the service life of concrete structures. Furthermore, frequently the physical attack by salt crystallization is being confused with the classical sulfate attack, which involves the chemical interaction between sulfate ions from an external source and the constituents of cement paste. In addition, there is also an internal sulfate attack –a chemical attack in which the source of sulfate ions resides in the concrete aggregates or cement–. Additionally, modern concrete as been affected by the products of microorganism metabolism, in particular sulfuric acid, this damage done to hardened concrete is known as concrete biodeterioration and also known as microbiologically induced corrosion of concrete (MICC). Being perhaps this biodeterioration the most important cause of concrete decay and perhaps the true explanation of sulfate attack on concrete. Some of the controversies about sulfate attack are addressed in this article, we have studied the case applying simple considerations concerning concrete composition and flouting at the same time some of the stricter observed paradigms in the cement and concrete industry. It is concluded that a holistic approach is necessary to separate the real causes of sulfate attack on concrete from the imaginary ones.