Proposal of a methodology for the preliminary assessment of kaolinitic clay deposits as a source of SCMs

The growing interest in calcined clays as Supplementary Cementitious Materials (SCMs), from sources other than relatively pure industrial grade clay deposits, demands the development of new tools for the identification and evaluation of the potentialities of a given clay deposit as a source of raw materials for the production of SCMs. In this paper, a methodology for the preliminary assessment of kaolinitic clay deposits as a source of SCMs is presented and discussed. As a case study, the chemical and mineralogical composition of several non industrial grade kaolinitic clay deposits, identified and classified according to the proposed methodology, is related to the pozzolanic reactivity of their calcination products. The developed methodology allows to establish preliminary selection criteria based on the chemical composition of the raw material (% Al₂O₃ > 18,0; Al₂O₃/SiO₂ > 0,3; LOI > 7,0; % CaO < 3,0; % SO₃ < 3,0). Comparison of the potentialities between the different clay deposits is determined from its relative position in a plot that relates the content of Al₂O₃ and the weight loss within the range of temperatures that corresponds to the thermal decomposition of clay minerals, which are, in turn, the main parameters affecting the pozzolanic reactivity of calcination products. The presence of thermally active non clay minerals in the sample may also affects negatively the pozzolanic reactivity. Through the observed results, the developed methodology proves to be a practical and useful tool for the identification and evaluation of kaolinitic clay deposits as a source of pozzolans.