Mechanical properties of blended cements affected by impurities in thermally activated clays

With the scarcity of raw materials, energy intensiveness and environmental burden connected with producing Portland cement, there is a growing need to find substitute binders. Thermally activated clay also appears to be a suitable material for partial cement replacement. However, not all clays are the same. It depends very much on the place of collection, its chemical and phase composition, and the activation temperature. This study compared six different types of clays fired at 600 °C in terms of quantitative phase analysis and mechanical strength results. In addition to the fineness of grinding and firing temperature, the clay composition had an immense impact on mechanical properties. Content of illite up to 20% was found to be beneficial, as this clay reached the highest mechanical strengths. Regarding the quartz, its presence did not harm the overall performance of thermally activated clays and the presence of calcite could cause the improvement of the mechanical strengths. However, the clay with the most miscellaneous composition caused the deterioration of compressive strength but reached much higher bending strength compared to pure cement.