Evaluation of red mud as filler in Brazilian dense graded asphalt mixtures

Abstract

Red mud is a waste resulting from the bauxite refining to produce aluminum. A large amount of red mud generated and inadequately disposed of in the environment, evidence the immediate necessity in developing methods to reuse this hazardous waste in the productive chain. In this scenario, a viable and environmental alternative is the red mud used as filler in asphalt mixtures production. This work aims to evaluate the potential application of red mud as filler in dense asphalt mixture. Three percentages of red mud as filler were tested (3, 5 and 7%). The methodology encompassed the red mud chemical analysis, the asphalt mixtures design and production, and then, mechanical tests, such as moisture-induced damage and, permanent deformation through French Rutting Tester (FRT) traffic simulator were performed. The red mud tests included X-ray diffraction, fluorescence, specific mass, laser granulometry, pH and scanning electron microscopy. As Brazilian dense-graded mixture allow the total filler content of 7%, in order to vary the red mud percentage, stone powder filler (size ≤0.075 mm) was also used. As a result, the granulometry test showed that red mud could be used as filler. The chemical analysis detected the presence of 0.20% of vanadium pentoxide (V2O5) indicating that red mud is a hazardous waste. Three asphalt mixtures were produced using different percentages of red mud, Mixture 2 (3% of red mud and 4% of stone powder); Mixture 3 (5% of red mud and 2% of stone powder); Mixture 4 (7% of red mud). The conventional mixture with 7% stone powder filler was the reference (Mixture 1). The moisture-induced damage showed that red mud mixtures presented greater tensile strength by diametral compression in comparison to the reference mixture. As for permanent deformation resistance, Mixture 3 (5% of red mud and 2% of stone powder) performed better than the others, with 3.50% of rutting depth at 30,000 cycles.c In general, concerning conventional mixture, red mud ones presented rutting reduction from 42.63% (reference) to 12.82 (mixture 3). This study showed the viability of reinserting the red mud in the production chain and the possible road construction use. The red mud as filler in asphalt mixtures production showed as an option to contribute and mitigate the disposal problems, as well, as an environmentally friendly alternative.