The Canadian Standard CSA CAN3-A5.M83 allows the addition of up to 5% carbonate additions for Type 10, normal Portland cement, and this allowance has recently been extended to Type 30, high-early strength cement. The possibility of extending the carbonate additions to the other cement types, including those for sulfate resistance and moderate heat of hydration, has been discussed by the A5 Committee, and some concrete test data have been presented. However, the initial results did not include testing for the effects on sulfate resisting or heat of hydration properties. Therefore, this study was initiated.
Pairs of samples of commercially ground cements from plants producing cements both with and without carbonate additions were obtained. This was done, in lieu of laboratory blends, since grindability and optimum sulfur trioxide (SO3) levels are influenced by carbonate additions and it was thought that laboratory ground cements would not represent the commercial reality.
Three pairs of cements with medium and high tricalcium aluminate (C3A) contents were obtained. Heats of hydration were measured at 7 days using ASTM Test for Heat of Hydration of Hydraulic Cement (C 186). Strength development and sulfate resistance were evaluated using ASTM Test for Compressive Strength of Hydraulic Cement Mortars (C 109), Test for Potential Expansion of Portland Cement Mortars Exposed to Sulfate (C 452) and Test for Length Change of Hydraulic Cement Mortars Exposed to Sulfate Solution (C 1012).
Results indicate that for the limited range of tricalcium aluminate (C3A) studied, carbonate additions do not significantly influence sulfate resistance or heat of hydration.