Effect of mixture composition and initial curing conditions on scaling resistance of ternary (OPC/FA/SF) concrete

This paper presents the results of a multiobjective laboratory study on scaling resistance of ternary concrete containing Class C fly ash (FA) and silica fume (SF). Several experimental variables were included in the research and statistical analysis was performed to examine specific effects of each of the variables on the amount of scaling. The first variable studied was the relative amount of FA (20 or 30% by mass of total cementitious materials) and SF (5 or 7% by mass of total cementitious materials) used in the ternary cementitious system. The second variable evaluated was the type of initial curing regime. The curing regimes compared included air drying, 3 days under wet burlap, 7 days under wet burlap, and application of curing compound for 7 days. The last variable assessed was the time of exposure to freeze-thaw (F-T) cycles in the presence of deicing salt, which included testing at either early age (14, 17, or 21 days depending on the initial curing regime) or at late age (90 days). The major finding from the research conducted was that the ternary mixtures containing 20% FA are much less prone to scaling than the mixtures with 30% FA. The mixtures with 20% FA were also found to be less sensitive (in terms of scaling resistance) to the initial curing conditions than mixtures with 30% FA. The late exposure to F-T cycles in the presence of deicing salt did not significantly improve the scaling resistance of any of the evaluated mixtures, most probably due to differences in scaling mode associated with the exposure times evaluated.