Research On Cold In-plant Recycling Technology Of Milling Materials For Old Asphalt Pavement

Recycling of asphalt pavement have the advantages of economic, energy-saving and environment friendly, which is conformity with the principles of "minimization""recycle" and "recycling". Taking use of these high quality waste road resources could reduce total social cost of engineering, mitigate environment crisis causing by contradiction between supply and demand of nature and human beings, social and environmental benefits. Recycling methods of old asphalt pavement include hot in-place recycling, cold in-place recycling, hot in-plant recycling and cold in-plant recycling, wherein, cold in-plant recycling has the characteristic of environment friendly, low energy consumption and simple process. In the paper, cold in-plant recycling of milling materials for old asphalt pavement is researched using laboratory test and experimental pavements,main content and conclusions are as follows:(1) Selection method for base asphalt of recycling agent has been studied, key technical indexes of agent are developed, such as stability, adhesion and penetrability of emulsion, demulsification speed and molding time. Temperature performance, ageing resistance and PG level were evaluated.(2) Compaction and curing method of cold in-plant recycling mixture are improved, and main points of mix design for cold in-plant recycling are proposed based on a fully analysis of milling materials performance, and. influence of water consumption on porosity of recycling mixture is also evaluated. The results shows that the improved Marshall design method could reflect process characteristics and molding mechanism of cold in-plant recycling mixture.(3) High temperature stability, low temperature crack resistance, moisture susceptibility, frost resistance and antistrip performance of cold in-plant recycling mixture were studied. Through comparison with HMA, road performance of cold in-plant recycling mixture was evaluated. The results shows that high temperature stability and moisture susceptibility of cold in-plant recycling mixture are as good as that of HMA, but other performances are relatively poor.(4) The influence of cement on road performance and mechanical property of cold in-plant recycling mixture was studied. The results show that cement could obviously improve the high temperature stability, moisture susceptibility, frost resistance and static and dynamic modulus of cold in-plant recycling mixture, however, it has unfavorable influence on fatigue performance and low temperature crack resistance and leads to a deterioration of mixture adhesion.(5) Experiment pavement of cold in-plant recycling mixtures were successfully constructed, method of mixture design and main points of construction for cold in-plant recycling mixtures were also summarized by comparison with series of recycling base layer. High and low temperature performance and resistance to water damage of cold recycling materials was evaluated by technical index of dynamic stability, bending strength and freeze-thaw split strength. Strength, rigidity and stability of cold recycling materials used for semi-rigid base course were evaluated by testing comprehensive strength, splitting strength and resilient modulus of recycling materials.(6) Stress distribution of cold in-plant recycling asphalt pavement with semi-rigid base course was analyzed with finite element analysis. The analysis shows that undersurface of asphalt surface is under compressed stress and the maximum tensile stress is at the center of wheel gap which is in tension, Top of subgrade soils is in compression; tensile stress of base layer recycled by emulsified asphalt is maximum and this type of base course showing obviously flexible characteristics, followed by regeneration cement base layer, tensile stress of gravel base layer stabilized by cement is minimum.