A Research On Durability Of Hot In-place Recycling Asphalt Mixture

The workload of highway maintenance is growing with days, as both construction and maintenance are progressing rapidly in China at present. The hot in-place recycle of HMA has significant social and economic benefits as a method of highway maintenance. The research of hot in-place recycle technology started relatively late in China. The hot in-place recycle pavement bears not only the vehicle load, but also the external environment such as freeze-thaw cycles and solar radiation, which would affect the durability of pavement.The proportion of regeneration agent in aged asphalt is determined to be 6.8% in this paper, by analysis of relationship between regeneration agent proportion and asphalt penetration, using penetration as a design index. SBS is decided to be added into recycled HMA with a proportion of 5% after comparing the modification effects of several modifiers. The optimum asphalt content in recycled asphalt mixture is determined by Marshall Test method. The pavement performances of recycled asphalt mixture satisfy the requirements of current Technical Specification for Construction of Highway Asphalt Pavement, tested in the laboratory.The splitting test and bending test are carried out in laboratory, simulating the external environment. Contrasted with new SBS modified asphalt mixture, the durability of recycled asphalt mixture is researched to draw the following regularity of variation mechanical indexes:(1) The splitting test after freeze-thaw cycles (25℃)The split tensile strength and the stiffness modulus of recycled asphalt mixture both get lower and more stable with the increase of freeze-thaw cycle times. The decreasing speed of split strength is basically the same with that of new modified asphalt mixture.(2) The low-temperature bending test after freeze-thaw cycles (-10℃)The flexural tensile strength of recycled asphalt mixture is higher than that of new asphalt mixture, getting lower and more stable with the increase of freeze-thaw cycle times; The flexural tensile strain of recycled asphalt mixture is higher than that of new asphalt mixture, getting higher with the increase of freeze-thaw cycle times; The stiffness modulus of recycled asphalt mixture get lower and more stable with the increase of freeze-thaw cycle times.(3) The splitting test after long-term aging (25℃) The split strength of asphalt mixture increases after long-term aging:19.2% for recycled asphalt mixture and 12.1% for new asphalt mixture. The damage tensile strain of asphalt mixture decreases after long-term aging:17.4% for recycled asphalt mixture and 12.2% for new asphalt mixture.