Particle characteristics of calcined clays and limestone and their impact on early hydration and sulfate demand of blended cement

Abstract

Supplementary cementitious materials (SCMs) can alter significantly the early hydration behavior of blended cement. While the underlying mechanisms have been intensively discussed in literature, they need to be extended regarding SCMs with complex mineralogy and surface properties, such as calcined clays. In this study, a blended Portland limestone cement was monitored during the first 48 h of hydration using in situ X-ray diffraction and isothermal calorimetry. The influence of a fine limestone and four different calcined clays, which vary in mineralogical composition and particle properties, was investigated at a replacement level of 30 wt%. The sulfate content was gradually adjusted and its influence on heat evolution and phase development was examined. It was shown, that depending on their particle properties, the investigated SCMs influence the aluminate and silicate clinker reaction by different mechanisms and to varying extents. The results underline the importance of proper sulfation of blended cements.