Caracterização da casca de café e suas cinzas na compatibilidade em matrizes cimentícias

Abstract

The present research aims to investigate the potential application of coffee husk ash as an additive in cement-based matrices, due to the abundance of residues from coffee production in Brazil. Its present physicochemical and morphological composition arouses interest in investigation, since research in the Cement Industry with the possibility of incorporating this material as additives is restricted. Therefore, combinations of "in natura" coffee husks, called Endocarp or Parchment, Mesocarp, Exocarp were characterized, in order to investigate chemical, morphological and thermal characteristics, by means of Scanning Electron Microscopy, Energy Dispersive Spectroscopy, Thermogravimetric Analysis and X-Ray Diffraction. After the characterization of the husks, the potential combination for the production of the ash was selected, these components of the coffee husks underwent heat treatment at a temperature of 500°C, 600°C, and 800°C, in order to guarantee the reduction of peaks of the crystalline elements and a consequent amorphization of these products. X-Ray Diffraction and X-Ray Fluorescence Assays were applied to evaluate the chemical composition of the produced ash and amorphism tendencies in the produced ash found in the ash produced at 600°C for 3 hours. In this way, the composites were prepared, with proportions of 5, 10, 15, 20, 25% (in relation to the cement mass) and reference paste (0%), to analyze the heat of hydration, through the test of Semi-Adiabatic Temperature Calorimetry, with the objective of investigating the reactivity of ash in the pastes, in which the highest substitution content makes the paste more reactive. And finally, considering the reaction content, the carbon fixation was evaluated, which is the evaluation of the Pozzolanicity of the material, however, the value found for the Pozzolanic Activity Index found was 155.08g /mg or 15.508%, so the samples did not reach the minimum value (75%) stipulated by NBR 12653/1992. Therefore, the results presented in this research, where the coffee husk ash were applied to cementitious matrices, it was not possible to prove its application as Supplementary Cementitious Material.