Evaluation of ultrafine calcined clays on LC3 cements on the sulfate requirement, water demand and strength development

The utilization of clays other than kaolinite, particularly ultrafine clays in ternary blended cement, and their impact on sulfate optimization still need to be better understood. This study investigated the use of high amorphous kaolinite clay and a kaolinite–hematite clay with a high specific surface area (SSA). The aim was to enhance understanding of sulfate balance and its influence on cement hydration when combining different metakaolin:limestone ratios with two different clinker substitution levels. First, sulfate balance was assessed using isothermal calorimetry test varying the total SO 3 content from 2.0 to 5.5%. Within the properly sulfated systems, bound water and portlandite content was evaluated by thermogravimetric analysis, setting times by Vicat’s needle test, minimum water demand by mini-slump spread flow test in cement pastes and compressive strength in mortars The results demonstrated a great influence of the additional surface area offsetting the amount of amorphous phase on sulfate optimization. Furthermore, the mechanical strength exhibited remarkable performance compared to an ordinary Portland cement (OPC) system, despite replacing over half of the clinker.