Influência do lixiviado de aterro sanitário nas propriedades de diferentes classes de concreto comerciais

Abstract

A relation between the generation of urban solid waste and its environmentally unsafe destination and/or the existence contaminated areas by irregular disposal are issues addressed in this research. These irregular areas are constantly occupied by buildings, which raises a concern with the potential interference of contaminants present in the concrete structure properties. In this scenario, the general objective of this work was to evaluate the exposure impact from landfill leachate on the concrete characteristics from different concrete commercial classifications (T1, T2 and T3). The proportion of ingredients for concrete T1 is poor, the proportion for concrete T2 is intermediate and the proportion for concrete T3 has the lowest w/c ratio and the highest cement consumption. The immersion of concrete specimens (CS) in a tank containing leachate aims an accelerated simulation. The characteristics of this leachate were monitored in the course of the experiment, as well the exposure of the physical/mechanical characteristics from concrete by compressive strength, electrical resistivity, water absorption, specific mass and void ratio tests. The XRF test, digital microscopy and SEM were also performed for this study. The monitoring of the leachate from the tank ("attack" environment) showed that the effluent maintained its degree of contamination. In this environment was verified that the physicochemical variations may be due to the degradation, sedimentation and evaporation processes, being also noticed the influence of the CS immersed in the tank. In the compressive strength tests, it was found that in 70.37% of the CS attack (tank with leachate) and CS reference (samples cured in a standardized environment for comparison) presented significantly equal results. In 25.92% of the attacked ones obtained superior results, and in 3.71% of the reference specimens reached superior compressive strength. In this way, it is estimated that the leachate did not negatively affect the strength of the concrete. However, it is notable that the leachate altered the surface of the concrete, resulting in the CS pores closing and its internal humidity reduction. This could be confirmed by comparing the water absorption and void ratio tests. This phenomenon may have influenced the increase in compressive strength and electrical resistivity tests. When comparing the mean electrical resistivity of concrete T1 there are no significant differences - a behavior that differs from that presented by concreteT2 and concrete T3, where the specimens in attack had a higher average than those in normalized cure. However, through the FRX analysis, qualitative, it was not possible to determine any change in the chemical composition of the samples. In digital microscopy images, it can be seen that the pores of the reference samples from concrete T1 are filled and those from concrete T3 are unobstructed. On the other hand, the attacked samples from concrete T1 and concrete T3 obtained the surfaces and pores with dark material, a possible biofilm, which contributes to the concrete impermeability. Finally, the MEV images show that the CSs that were in the reference environment presented structures that may be associated with the presence of ettringite, calcium hydroxide and C-S-H. These substances were not visually observed in the “attacked” CS. Based on these analyses; the research concludes that alterations caused by contact with leachate in concrete could be identified. These changes are associated with an increase in compressive strength and electrical resistivity; in addition, reducing the void index and water absorption.