Sustainable asphalt mixtures: enhancing environmental impact by partial fine aggregate substitution with rubber powder and bitumen modification using Nano-SiO2

The costs of producing asphalt mixtures are increasing day by day, and with the expansion of roads, the use of natural resources of aggregates has also increased. On the other hand, several factors, such as the increase in traffic load and the number of vehicles, intensify the stress in the pavement layers, reduce the service life of asphalt pavements, and increase the cost of maintenance of road pavements. For this reason, researchers are striving to reduce the costs of asphalt mixture production and the need for natural aggregates by taking advantage of rubberised asphalt in this field. However, when using rubber powder as aggregate, some weaknesses are observed in this mixture, which this study strives to solve by modifying bitumen and improving its performance. The objective of this study is to evaluate the effect of bitumen modified with Nano-SiO2 on the mechanical properties of rubberised asphalt mixture. The percentages of Nano-SiO2 are 0, 0.3, 0.6, 0.9, and 1.2% by weight of bitumen, and used rubber powder has been replaced with fine aggregates with different percentages of 0, 1, 3, and 5%. The characteristics investigated in this study are rutting and fatigue, evaluated in various laboratory conditions. Considering all three target criteria of this study (i.e. environmental, economic and technical), an asphalt mixture containing 3% rubber powder and 1.2% Nano-SiO2 can be considered the best combination to deal with rutting and fatigue. A combination by replacing 3% of aggregates with rubber powder, needs less to extract natural aggregates resources, and also the use of a waste material whose depot in nature is known as an environmental problem in the construction of new asphalt mixture. In addition to environmental aspects, This sample fatigue resistance is about 5%, and the rutting resistance is about 17% more than the control specimen (without additives).