Professor, University of Calgary, Calgary, Alberta
Delayed ettringite formation (DEF) is only one of a number of chemical and physical attack mechanisms related to the presence of sulfur-based compounds existing within the microstructure of concrete. Identification of the various “sulfate” attack mechanisms, both internal and external, is important to guide the development of appropriate performance-based test methods. Such test methods must also recognize and account for the fact that real deterioration processes in concrete often involve a combination of mechanisms; sulfate attack, for example, is often found in combination with other attack mechanisms, such as alkali-aggregate reaction or freezing and thawing. Thus, future tests or suites of tests should be designed to account for acceleration of deterioration that results from the synergy between attack mechanisms. It is suggested that a holistic approach—similar to that proposed by Mehta—whereby the effect of (a) combinations of raw materials and (b) combinations of environmental influences should play a central role in the development of new standards.
In this paper, an engineering view of the various mechanisms of sulfate attack is provided. Sulfate-attack mechanisms are categorized and major influences upon these mechanisms are briefly reviewed. The suitability of two key tests related to sulfate attack is examined—ASTM methods C 1012 and C 1038. Available data concerning test method C 1038 are analyzed. Because of the lack of confidence that C 1038 is an adequate performance test, reliance upon prescriptive limits for sulfate and aluminate contents and their relative proportions is currently a better approach to ensure adequate performance of cementitious systems in practice.
Paper ID: CCA10477J