Influence of Cement Replacement by Calcinated Kaolinitic and Montmorillonite Clays on the Properties of Mortars

Abstract

This study aims to investigate the decomposition and pozzolanic reactivity of two different clays (kaolinitic and montmorillonite) from different origins and to determine their effects after calcination on the properties of cement mortars when used to replace Portland cement partially. Mineralogical and chemical compositions of the clay samples were determined using XRD (X-ray Diffractometer) and XRF (X-ray Fluorescence) tests, respectively. TG-DTA (Thermogravimetry-Differential Thermal Analyses) was used to determine the temperature profiles and the burning temperatures of the clays. The density and fineness of the burnt clays were also determined. In order to investigate the optimum material properties, different burning temperatures and replacement levels were considered. It was found that for all temperatures, the two burnt clays possess good pozzolanic activity. The highest compressive strength and lowest water absorption capacity were achieved when the clay determined as kaolinitic was burned at 700 & DEG;C and with 10% replacement level. While for the clay determined as montmorillonite, the optimum properties were obtained at 700 & DEG;C with a 20% substitution level. Kaolinite had better pozzolanic reactivity than montmorillonite, achieving higher strength performance with lower water absorption when partially replaced with cement. Moreover, it had compressive strength values even higher than plain cement.