Multi-parameter study of external sulfate attack in blended cement materials

A conventional solution in reducing the potential damage in concrete structures from external sulfate attack is to partially replace the Portland cement with appropriate fly ash. Presently, the compatibility of fly ash as a remedial cement substitution is based on empirically developed ASTM classifications. With proper testing techniques and multi-parameter approaches, one can better correlate the properties of blended cements with the expected level of damage. In this paper, parameters affecting the sulfate resistance of concrete are reviewed and the modifications to conventional expansion tests are discussed. The role of fly ash chemical composition on the level of damage was studied experimentally at macro and micro-scales. The linear expansions were determined both in paste and mortar systems using standard size and modified size specimens. Microstructural studies using ESEM and quantitative EDS were used to characterize the nature of reaction products and fronts. Statistical analysis of data indicated that the sulfate resistance of cementitious materials is significantly influenced by the chemical composition and the transport properties of the system which can be improved by appropriate fly ash substitution. It is also demonstrated that the study of these mechanisms can be expedited using modified size specimens.