Sustainable crumb rubber modified asphalt mixtures based on low-temperature crack propagation characteristics using the response surface methodology

Fracture regime of asphalt concrete is of utmost importance in the sustainable design of optimized mixtures against low-temperature cracking. The energy dissipated in blunting the crack tip, stable crack growth, as well as post-peak resistance of the mixtures to the propagating crack comprise the overall fracture performance of the mixtures. In this research, employing the fracture resistance curve (R-curve) concept, three energy parameters: cohesive energy, fracture energy, and energy rate, are extracted to quantify the crack propagation regime of the mixtures incorporating ground recycled waste tire. A temperature range of 0 °C to −20 °C with 0 %, 10 %, and 20 % crumb rubber contents (CRC) were considered and the experiments were carried out in Single Edge notched Beam (SE(B)) fracture testing protocol. An environmental index comprising CO2 and CH4 emissions, as well as the energy consumption, was developed and the production cost of AC samples were also determined. A design of experiments based on the Central Composite Design (CCD) is applied. The Response Surface Methodology (RSM) is used to develop the best model between the fracture response, environmental factor, cost, and the input mixture properties. Multi-objective optimization scenarios were assessed by the RSM and a 4.74 % binder content with 19.5 % crumb rubber incorporation was resulted as the optimal mix design for maximum fracture response and minimized cost and environmental concerns in low temperatures. The environmental effects and costs were by average reduced by 15 % and 1 %, respectively and fracture responses have been improved compared to the reference optimum mix design (CRC = 0).