Mechanical properties of concrete made with calcined clay: a review by RILEM TC-282 CCL

A review of the mechanical property development of concrete containing calcined clay was performed. A comparison of compressive and tensile strength results showed that concrete can be made to have equivalent or higher strength as an ordinary portland cement (OPC) system with up to 30% calcined clay or 50% blend of calcined clay and limestone fines in a limestone calcined clay cement (LC³) system, as long as the kaolinite content in the clay used is above 40%. Most of the strength development in these systems occurs during the first 7 days, making extended wet curing not necessary in these systems. Calcined clay systems are subject to the cross-over effect because of the high solubility of ettringite and lower cement degree of hydration at elevated temperatures. Concrete creep and shrinkage were found to be a function of the clay kaolinite content and replacement level. Bond strength was improved by the use of up to 20% metakaolin.