Incorporation of Calcined Clays in Mortars: Porous Structure and Compressive Strength

During the last decades, there has been an increasing interest in the cement industry to incorporate pozzolanic materials to cement in order to reduce CO2 emissions, and increase the strength and durability of mortars and concretes. In this work, the potential use of two thermically activated kaolinitic clays as pozzolanic materials coming from different deposits of Argentina, is studied. Both Kaolinitic clays have different kaolinite content and a different order-disorder structure. After thermal treatment and grinding, their pozzolanic properties were studied on blended cement containing 30% of calcined clays. It was determined that mortars containing calcined clay with a higher percentage of kaolinite and certain disorder degree in its crystallinity previous to calcination, developed higher resistance to compression. This can be attributed to larger quantity of hydration products caused by the pozzolanic reaction, which also produces a better pore size arrangement. To conclude, when kaolinitic clays are used as pozzolana, kaolinitic percentage and structural disorder are variables to be taken into account.