Chemical characterization of Cretan clays for the design of restoration mortars

Three clays and a marly-limestone from the West of Chania, Crete, fired at temperatures ranging from 200 to 1200 degrees C, were characterized by XRD, FTIR, EDXRF and wet chemical analyses. The aim of this study was to assess the pozzolanic and hydraulic properties of these materials for potential use as binders in the design of restoration mortars. The mineralogical composition of the clays is quartz, illite, calcite, plagioclase, kaolinite and hematite. The identification of larnite and gehlenite in the calcined marly-limestone established it as potential cementious binder. Among the clays, one with low amount of calcite and considerable kaolinite content exhibited the best pozzolanic activity upon heating at 600 degrees C. Therefore, it can be considered as an appropriate material for restoration purposes. It is deduced that the pozzolanic activity of fired clays is greatly dependent on the firing temperature and is enhanced in clays containing low calcite and high kaolinite amounts.