Autogenous shrinkage of limestone and calcined clay cements

Abstract

Reducing the clinker factor is a target with increasing priority in cement industry, as a solution to lower greenhouse gases emissions and increasing cement production. Replacing a fraction of the clinker from the kiln with supplementary cementitious materials (SCMs) has proven efficient for many decades. Calcined clays are good candidates for SCMs, as the raw material can be found in many parts of the world, especially developing countries. Limestone and calcined clay ternary cements show a great potential as building material and mechanical properties close to OPC. On the other hand, little is known about the shrinkage behavior of such systems. Assessing this phenomenon is of prime importance for the elaboration of blends bound to be used for building purposes, as those mixes are controlled by strict standards in each country. Therefore, the mechanisms causing autogenous strain in such systems need to be understood. Ternary blends, such as Portland cement with blast furnace slag and limestone, tend to have a different strength development than OPC, therefore modifying their response to internal stresses caused by self-dessication, among other phenomena. However, no precise study on shrinkage behavior of limestone and calcined clay systems has been reported yet. Autogenous shrinkage measurements were done according to the actual standards and compared to OPC. In addition, clays with different grades of kaolinite were tested. Kaolinite is transformed into reactive metakaolin by the calcination process. Therefore, the impact of impurities or other phases, in particular expanding clays such as smectite, is studied.