Mix ratio optimization design method for hot in-place recycled asphalt mixtures

The design of components for hot in-place recycling (HIR) is the key to determining the performance of asphalt pavement regeneration. However, existing design methods have numerous problems, such as the large demand for sample size, and the neglect of the interaction of different factors and levels. In order to establish a reasonable component design method for hot in-place recycled mixtures, this study analyzed the action mode of the rejuvenator and optimized the mix design method using orthogonal tests. The regeneration mechanism of the rejuvenator in the reclaimed asphalt pavement (RAP) was analyzed and the optimum working conditions of the rejuvenator were determined initially by means of physical performance, chemical composition and dynamic shear rheological tests. In addition, the influences of rejuvenator, RAP and new asphalt at high and low temperatures and the water stability of the recycled asphalt mix were analyzed, with testing using an orthogonal design method combining rheological tests for wheel rutting, trabecular bending rheological and freeze-thaw splitting tests, the optimum design of the recycled mixture was determined on this basis. According to the test results, the rejuvenator and RAP can influence the pavement performance of the recycled mixture more than new asphalt. When the rejuvenator dose is 5.% of the total asphalt mass, the ratio of RAP and new asphalt is 80% and 0% of the mixture, respectively, the recycling effect is the best. The proposed method is economical and environmentally friendly and has been well applied in ordinary trunk road maintenance engineering in Hanzhong City, Shaanxi Province, China, since 2017. The research findings can provide references for HIR engineering.