Performance of geopolymer tiles in high temperature and saturation conditions

Abstract

High temperature and saturation situations are conditions that a building material can experience due to fire, heavy rains and floods, for example. For this reason, the application of geopolymer tiles in conditions of high temperature and saturation was evaluated in this work, to understand how fires and rains modify the performance of these materials. Samples were produced varying the molar ratio of SiO2/Al2O3 between 2.25 and 4.00, curing at an ambient temperature of 25 °C at 7 and 28 days. Metakaolin, sodium hydroxide, sodium silicate and water were used as raw materials in this study. Initially, the samples were evaluated in normal condition performing tests of flexural tensile strength, linear shrinkage, density, optical microscopy (OM) and mineralogical analysis. It was found that formulations 2.25, 2.50 and 3.00 had compatible properties, while formulations 3.50 and 4.00 did not show efficiency in the geopolymerization reaction due to the excess of sodium in the material. Formulations 2.25, 2.50 and 3.00 formed larger amounts of zeolite A (sodalite cage) and zeolite X (faujasite), which are minerals formed after the geopolymerization reaction. This did not happen with formulations 3.50 and 4.00. In the sequence, the high temperature condition was carried out until the temperature of 1050 °C, being carried out tests of burning linear shrinkage, mass loss, flexural tensile strength and thermal analysis. The results showed that due to the non-formation of polysialate networks in an effective way, formulations 3.50 and 4.00 showed a high drop in properties, differently from formulations 2.25, 2.50 and 3.00, that present efficient polysialate networks, due to the formation of zeolites X and zeolites A. Finally, the saturation condition was performed, where open porosity, water absorption, OM and flexural tensile strength were evaluated. It was observed that the formulations 3.50 and 4.00 showed elimination of sodium gels during saturation, which caused a decrease in the mechanical performance of the material. In all conditions, formulations 2.25, 2.50 and mainly 3.00 showed better results. Finally, geopolymers tiles with SiO2/Al2O3 = 3.00 was evaluated in a complementary manner by scanning electron microscopy (SEM), where it proved its compatibility with the application proposed in this work.