Influence of C\u3csub\u3e3\u3c/sub\u3eS Content of Cement on Concrete Sulfate Durability

The influence of tricalcium silicate content of cement on concrete durability has long been a topic of discussion in the literature. The objective of this investigation was to determine whether increasing tricalcium silicate content of cement has a negative effect on concrete sulfate durability. Several mill certificates were reviewed to select cements with similar tricalcium aluminate content and variable tricalcium silicate contents. Cements selected for this study were randomly labeled as cements C, D, D2, E, and P. The following properties were assessed for the as-received cements: Blaine fineness, particle size distribution, chemical oxide content, and mineralogical content. Three different methods were employed to determine the mineralogical composition of the as-received cements: Bogue calculation, internal standard method, and Rietveld refinement analysis. Despite the attempt to select cements with similar composition, it was determined that the as-received cements had compositional differences other than their C3S content. These cements had a variable tricalcium aluminate and alkali content, as well as differences in the amount and form of calcium sulfates. In order to eliminate these variances, doped cements were prepared by increasing the C3S content of the as received cements to 69 % by Bogue calculation. Durability of as-received cements and doped cements was assessed through several measurements including length change, compressive strength, and phase transformation in sodium sulfate solution. For as-received cements, compressive strength of mortar cubes stored in saturated lime solution was evaluated as well. Semiquantitative x-ray diffraction analysis and scanning electron microscopy observations were performed on mortar bars to evaluate the relative amounts and morphology of the hydrated phases. It was concluded at the end of this study that cements with high tricalcium silicate content generally have poor durability in sodium sulfate environment. All the cements experienced higher expansion with increased C3S content. High C3S content combinedwith high C3A content was particularly detrimental to mortar resistance to sodium sulfate attack