Contribuição para o estudo da degradação química da pasta de cimento: simulação da atividade agressiva do guano de morcegos

Abstract

The concrete, due to its high strength, low cost and moldability, is the most popular building material at the moment when compared with other materials used for the same purposes. In this context, with the continued growth of urban areas, the number of buildings and large roads structures has also increased. For this reason, many animal species have had to adapt themselves to these new environmental conditions and have started to use human buildings, which can often simulate nature conditions, as shelters. Thus, the metabolism waste resulting from these animals began to chemically interact with these building materials, causing substantially degradation. The main aim of this work is to show how the biological waste, in this case, bat guano, can promote chemical degradation of the cement paste. To that purpose, the chemical attack of cement hardened sampleswas realized in different exposition times in with aqueous solutions of nitric acid and sulfuric acid at pH 4.5, simulating the bat guano oxidation conditions, where these acids, among other substances, are formed. The results indicate that nitric acid is more aggressive to cement paste than the sulfuric acid as evidenced by electron microscopy images where there was a more intensive deterioration of the cement matrix on the surface of cement hardened samples. The images generated by the X-ray microtomographyshowed that there is a difference on density of the cement matrix in the region chemically attacked, in particular when the sulfuric acid was used, which can be associated with the corrosion product properties formed due the sulfuric acid reaction with the cementitious matrix. The hardened cement paste samples showed mass increase with exposition time, probably due to the respective calcium salts deposition on the surface formed as products of chemical attack.