Resíduo da bauxita na produção de agregados graúdos sintéticos para concreto estrutural: análise de durabilidade

Abstract

In the midst of environmental policies, civil construction began to seek alternative materials, such as those arising from industrial waste; and with each passing day this has become more common. This fact is related to issues involving: the high demand for construction materials; the depletion of raw material reserves; the high cost and space of waste storage; and possible risks to public health arising. In the case of industrial waste, mining waste should be highlighted, in particular the bauxite residue (BR) resulting from the Bayer ore refining process, which has already become a promising alternative raw material in several countries, including Brazil for a number of applications. The BR has been studied and used somewhat recently in the production of coarse aggregates for concrete, with success in several studies. However, the information available regarding the use of coarse synthetic aggregates in concrete is mostly linked to its physical-mechanical properties, with a certain lack of data regarding their influence on the durability of structural concrete. The study initially addressed the physical mechanical characteristics and reactive potential by alkali-aggregate reaction (AAR) of 3 coarse synthetic aggregates (AGS 70, AGS 80 and AGS 90), obtained from BR together with silica and clay, based on in the normative requirements required for use in concrete. Soon after, the concrete produced with these aggregates, in total replacement of pebbles, were evaluated regarding their physical-mechanical properties (resistance to axial compression, traction due to diametric compression, modulus of elasticity, water absorption by capillarity) and durability (accelerated carbonation and penetration of chlorides). The results showed that the synthetic BR aggregates were consistent with the technical specifications for use in structural concrete and did not trigger AAR, thus remaining inoculum. The axial compression strength (28 days) reached values between 36-24 MPa; traction and modulus of elasticity showed little variability; capillary absorption was proportional to the increasing linear trend of water absorption by coarse aggregates; highlighting the concretes with AGS 70 and AGS 80 that obtained better performance in the physical-mechanical characteristics analyzed. The carbonation resistance of concretes containing AGS 70 and AGS 80, based on normative references, were classified as low and exceptional respectively. Regarding the penetration of chlorides, they were classified as moderate resistance (with AGS 70 and AGS 80) and low (with AGS 90) according to the methodology used.