Incorporação de resíduo agroindustrial em matrizes cimentícias

Abstract

The proposal of this research covers two important subjects: the application of a waste generated in large scale in Brazil and the study of properties related to the durability of cement matrices. Brazil leads the world's sugarcane production. Among the wastes generated in sugarcane processing, bagasse stands out due the utilization as biomass to generate energy. After the burning of bagasse, the sugarcane bagasse ash sand (SBAS) remains at the bottom of the boilers. The final disposition of this material is a problem faced by the managers of the sugar and alcohol plants. In this context, the main objective of this study was to evaluate the influence of the SBAS incorporation on the porosity of the cementitious matrices, susceptibility to the aggressive agents ingress, and on the passivation of the steel. Therefore, the study was carried out in three phases. In the first stage a process of beneficiation, characterization, and verification of the pozzolanic activity of SBAS samples with different particle size distributions was performed. In the second phase, a study in the mortar phase applying the SBAS in partial replacement of the natural sand in the contents of 0%, 10%, 20%, 30%, and 40% (by volume) was carried out. Several tests were carried out to verify the influence of SBAS application on mortars, such as: compressive strength, water absorption by immersion and capillarity, mercury intrusion porosimetry, tomography, electrical resistivity, chloride penetrability, scanning electron microscopy, hydrogenation potential, electrical conductivity, among others. In the third stage, the steel passivation process was verified when exposed to the pore water solution with and without SBAS by monitoring the open circuit potential. Subsequently, the passivating films were analyzed by scanning electron microscopy technique. Through of the obtained results it can be verified that the ashes analyzed showed low pozzolanic reactivity. The SBAS incorporation contributed to the reduction of macropores, increased the electrical resistivity, and reduction of the chloride penetrability, for the mortars with advanced ages (after 91 days), compared to the reference mortar (0% SBAS). The passivating film formed by the pore water solution with SBAS stabilized at a more positive potential than the reference. In addition, it was possible to identify higher amounts of calcium oxides on the surface of the steel exposed to the SBAS solution when compared to the reference. These results indicate a possible improvement in the quality of the passivating film formed in solution containing SBAS. Finally, it can be concluded that the incorporation of SBAS improved properties related to the durability of the matrices studied.