Sulphate Optimization of Binders with Calcined Clay Using Isothermal Calorimetry

The concept of using isothermal calorimetry for sulphate optimization of Portland cement was developed by Lerch more than 70 years ago. In this paper, we demonstrate a new calorimetry based approach for modern low clinker blended cements grounded in Lerch’s concept and that can be used for both periodic sulphate optimization and continuous process control to ensure optimum performance during daily cement production. More frequent sulphate optimization, coupled with daily process control, is especially important for binders that rely on optimum aluminate hydration, such as the novel LC3 cement that utilizes aluminate phases from both clinker aluminates and calcined clay. In the LC3 cement, the sulphate component is the major phase controlling the early hydration, strength development and admixture compatibility of the alumina bearing phases. Moreover, the calorimetry based approach described herein can be substantially automated and does not require a traditional laboratory setting, nor air conditioning, since the calorimetry itself provides a laboratory environment in its temperature control chamber. The only manual labour required for this concept is the weighing of binder, water, calcium sulphate and optional admixtures. The mixing, data collection, calibration, evaluation of the sulphate optimum and subsequent process control can all be automated, such as in Calmetrix Inc’s software suite for cement research and development.