Evaluation of optimum mixing conditions for rubberized asphalt mixture containing reclaimed asphalt pavement

Abstract

The use of reclaimed asphalt pavement (RAP) represents an environmentally positive method of recycling besides saving cost. Experience has shown that properly designed hot-mix asphalt (HMA) containing RAP performs as well as HMA produced with virgin materials. Crumb rubber asphalt represents, on the other hand, a promising paving material that recycles waste tires. The combination of the two techniques has promising environmental significance, i.e. recycling asphalt concrete pavement using rubberized asphalt, which remains a virgin research topic. In this paper, microstructure of rubberized asphalt mixture containing RAP was studied to obtain its optimum mixing conditions. Specimens were prepared in the laboratory and scanned by X-ray Computed Tomography (CT) system to identify distribution of the components. An improved Otsu’s algorithm was used to segment the mixture images. The results indicate that the algorithm could effectively solve the uneven brightness problem of scanned images. Statistical indicators were used to analyze uniformity of component distribution. Three mixing time and three mixing temperatures were used in the blending process to evaluate effects of mixing time and mixing temperature on the distribution of mixture component. It was found that distribution of air voids and virgin aggregates are relatively more sensitive to mixing time and mixing temperature. Optimum mixing time is 150 s and it should not be less than 90 s to achieve well distribution of components. Optimum mixing temperature is at least 150 °C.