Avaliação mecânica e térmica de misturas asfálticas modificadas com micropartículas de dióxido de titânio

Abstract

Recent research on the factors that influence urban climate recognizes that the increase in temperatures in urban centers, resulting in the phenomenon of Urban Heat Islands, is due to anthropogenic activities, such as land use and occupation. Due to the harmful consequences of this effect, it is necessary to develop methodologies to mitigate it. One promising approach involves the use of urban pavement surfaces with lighter colors, capable of reflecting a greater amount of solar radiation, through the incorporation of dyes or other materials into the pavement. In this sense, titanium dioxide (TiO₂) has gained prominence in recent research in the area of paving, especially as a modifying agent for asphalt binders. However, given the gaps observed in the literature, it is still necessary to investigate the effects of the addition on the mechanical behavior of asphalt mixtures, in addition to verifying its thermal effects in relation to its ability to modify the color of the mixture. In view of this, the study in question evaluated the mechanical and thermal effects of the addition of TiO₂ in hot asphalt mixtures. TiO₂ was used as a partial and total filler replacement, in proportions of 2% and 3% by weight of the mixture. Indirect tensile strength (ITS), moisture damage susceptibility (ITSR), resilient modulus (RM), abrasion wear, permanent deformation resistance (FN) and indirect tensile fatigue life tests were performed. To evaluate the effect of aging on the mechanical strength of the mixtures, the Short Term Oven Aging (STOA) protocol was applied. A factorial design was also performed for the mechanical results of the mixtures. For the statistical analysis, a two-way ANOVA with repetition was performed. The thermal analysis involved verifying the albedo value and the surface and internal temperatures of the mixtures. A preliminary analysis of the economic feasibility for using the material was also performed. The mechanical results demonstrated that the 2%TiO₂+1%Cal and 3%TiO₂ mixtures presented, respectively, an increase in ITS of 7.41% and 14.07%, a reduction in moisture damage of 2.22% and 6.65%, a decrease in abrasion wear of 31.41% and 52.64%, and a reduction in FN of 10.78% and 22.55%. As for RM, an increase of 12% was observed in the 2%TiO₂+1%Cal mixture, while the 3%TiO₂ mixture showed a reduction of 19% in this parameter. Regarding indirect tensile fatigue life, the mixtures with and without TiO₂ showed similar performance. In general, the application of the aging protocol indicated that, with the effect of time, the performances of the mixtures with the addition of TiO₂ resembled those of the reference mixtures, with the 2% TiO₂+1% Lime mixture presenting greater stability of the mechanical parameters after aging. The thermal analysis demonstrated that the 3% TiO₂ mixture presented superior performance in relation to the others, standing out for the greater increase in albedo and the greater reduction in surface temperature. The 2% TiO₂+1% Lime mixture also obtained satisfactory results, superior to those of the reference mixture, although slightly inferior to those of the dosage with 3% TiO₂. The application of the STOA aging protocol showed an improvement in the evaluated thermal parameters of all mixtures. Based on the internal temperature analysis performed on the reference and 2%TiO₂+1%Cal mixtures, it was observed that the surface heats up and cools down more quickly than the internal layers, where heat is absorbed and stored, keeping the interior of the mixture heated for longer periods. In all layers of the 2%TiO₂+1%Cal mixture, temperatures remained lower compared to the reference mixture. Considering the preliminary analysis of economic viability, although titanium dioxide presents a higher unit cost, the association of mechanical and thermal gains observed in the mixtures evaluated indicates that its application in asphalt compositions may be technically and economically viable. It is concluded that, given the mechanical and thermal results and the preliminary analysis of economic feasibility, the incorporation of titanium dioxide in asphalt mixtures has the potential to improve pavement performance, contributing both to their durability and to the mitigation of thermal effects in urban environments.