The fundamental knowledge about the reaction mechanism of calcined clays in cement and the mutual interaction is important for their assessment as supplementary cementitious material and the resulting concrete properties. In this study, the hydration of two cements differing in alkali content and with the addition of a highly reactive, aluminum-rich metakaolin and one calcined common clay with low kaolinite content was investigated during the first 48 hours. For this purpose, four established methods that describe the early hydration were used: isothermal calorimetry, thermogravimetry, in-situ X-ray diffraction and chemical analysis of pore solution. This so far unique combination of methods enabled the understanding of the complex binder (cement-calcined clay) hydration behavior. The results showed considerable differences depending on type of calcined clay, its chemical-mineralogical composition, fineness and especially towards its reaction mechanism with aluminate clinker phases controlled by the composition of pore solution. The impact of calcined clay on the early clinker hydration exceeds significantly physical effects only.
Performance of Blended Cements with Limestone Filler and Illitic Calcined Clay Immediately Exposed to Sulfate Environment