Material Alcalinamente Ativado (MAA) de metacaulinita sintetizado a partir das espécies alcalinas do tipo sódio e potássio

Abstract

New materials have been developed seeking to minimize negative effects on the environment, especially in the field of cementitious materials, alkaline activated materials (AAM). These have been shown to be an economically viable alternative that may contribute to reducing the environmental impact of construction in general. The raw material for the production of this material must be rich in silica and alumina in amorphous form. In this work, metakaolinite was chosen because it is a locally available material, relatively easy to obtain and low production cost. The efficiency of activation depends on the chemical and mineralogical composition of the raw material, as well as the molar ratios of the components and the curing conditions. Alkaline activators were defined as sodium and potassium hydroxides and silicates. Although there are already works in this field, here the research sought to advance by studying the formation of silicoaluminous species of the (AAM) at curing temperatures of 38.5oC and 50oC, lower than those commonly indicated, and using also the molarity of alkaline activators equal to 8, which corresponds to about half of what is considered ―ideal‖ by the literature. This is to reduce the energy costs of chemicals. The behavior of MAA was evaluated when subjected to thermal curing at temperatures indicated for periods of 3, 7, 28, 56 and 91 days. The generated AAM's were sprayed and characterized by physical-chemical tests using X-ray diffraction and fluorescence techniques (DRX and FRX), as well as by thermographic tests, infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and electron microscopy by scanning (MEV). In addition to these, the mechanical performance of AAM‘s was obtained in tests of resistance to compression, whose results were analyzed statistically through ANOVA. The characterization results made it possible to know the physical-chemical and microstructural characteristics of the products, as well as their reaction process. Using Fourier transformation infrared spectroscopy it was possible to identify the reactive potential of the samples. The results of compressive strength were worked from the influence of alkaline activators (NaOH and KOH); the different temperatures (38.5 °C and 50 °C); of curing time at ages 3, 7, 28, 56 and 91 days and indicated that there was no differentiation in the variability of resistances in relation to the alkaline activators used. For NaOH, there was an oscillation from 19.88 MPa (3 days) to 6.16 MPa (91 days) at a temperature of 38.5 ºC, and 19.45 MPa to 6.03 MPa (3 days and 91 days respectively) at temperature of 50 ºC. For KOH, the variation was 12.47 MPa (28 days) to 6.62 (91 days) at 38.5 ºC and, at 50 °C, 11.88 MPa (28 days) to 9,05 MPa (91 days). Taking into account the curing times, it is noticeable that when the curing time increases, the resistance of the products tends to decrease. Finally, statistically, in the resistance associated with the temperature, the results achieved at a temperature of 50 ºC were higher than that of 38.5 ºC. In this context, the developed AAM´s present themselves as products that promise significant performance in civil construction as sealing or interlocking blocks, with the advantage of being able to be prepared with a lowest mass percentage, low temperature, in shorter curing time and with a precursor of easy and abundant access, thus becoming a product less aggressive to the environment.