Increasing the kaolinite content of raw clays using particle classification techniques for use as supplementary cementitious materials

The adoption of blended cements to reduce the carbon footprint has increased significantly over the last decades. Clays containing kaolinite are a promising choice due to their widespread availability. Kaolinite content is the major factor controlling the performance of blended cements incorporating calcined clay, for example in LC3-50 (50% clinker, 30% calcined clay, 15% limestone and 5% gypsum) clays with a kaolinite above about 40% are needed to achieve similar strength to reference OPCs at 7 days. Materials with low contents of kalinite are often considered unsuitable. This study compares two fractionation techniques to increase the kaolinite content of a low-grade clay (30% kaolinite content). The results show that kaolinite remains concentrated in the fine particles after grinding. Both wet sedimentation and air separation were effective to increase the reactivity of the material as a combined result of increased fineness and kaolinite content. For the air separation process, it was observed that a significant amount of kaolinite remained in the rejected fraction after processing due to agglomeration of the powder. It was shown that the use of grinding aids before the separation process can further improve the results. (C) 2020 Elsevier Ltd. All rights reserved.