Thermal Activation of Two Complex Clays (Kaolinite-Pyrophillite-IUite) from Tandilia System, Buenos Aires, Argentina

摘要

The aim of this work is focused to identify natural resources with industrial potential to be used as supplementary cementitious materials (SCMs) in Portland blended cements. Two clays obtained from the quarries near to Barker in Tandilia System (Buenos Aires- Argentina) were studied. The geneses of these rocks are by a hydrothermal alteration and include the presence of pyrophillite. Whole-rock were characterized by XRD and FTCR spectroscopy indicating that main clayed minerals are kaolinite (Si2Al2O5(OH)4), illite (K_(0.66)Si_(3.33)Al_(2.66) Oio(OH)2) and pyrophillite (Si4Al2Oio(OH)2) associated with feldspar. The thermal transformation was studied by differential thermal analysis and the phase changes were confirmed by XRD and FTIR. Samples of clays were calcined at different temperature (550 to 1050 °C), the electrical conductivity was measured and the dissolved silica in simulated pore water solution was quantified. The pozzolanic activity was measured by the compressive strength activity index, on blended cement mortars containing 25% by weight of calcined clays. Results showed pozzolanic activity after 7 days and the compressive strength values exceed the rate of replacement for both clays. The high water demand of sample containing pyrophillite can be attributed to the exfoliation that occurs during the water loss process.