| As the highway construction in China has entered the period of large-scale maintenance,the concepts of "energy conservation and emission reduction as well as recycling utilization of resources" have been the green development concept of transportation industry gradually.Therefore,the pavement recycling technology has attracted more and more attention.Meanwhile,the understanding of recycled technology itself is more calm and scientific.For example,there is still some distance from the real eco-friendly transportation for the hot mix recycled asphalt(HMRA)technology in plant,which is accepted earliest and most widely used.Because it possesses the disadvantages of low utilization of reclaimed asphalt pavement(RAP),usually lower than 30%,and high construction temperature at which a considerable amount of exhaust gas and asphalt fumes is produced.How to reuse RAP efficiently on the premise of energy conservation and environmental protection is the key of the current research of asphalt pavement recycling technology and pavement maintenance.The high-percentage warm mix recycled asphalt(WMRA)technology with the advantages of both warm mix asphalt(WMA)and HMRA,can decrease the construction temperature effectively and increase the percentage of RAP.Nowadays,the high-percentage WMRA technology in China has not been mature enough as a result of the lack of systematic and comprehensive evaluation system and sufficient experimental data.Furthermore,the thorough evaluation system is required to build.Then the large-scale application of this technology will be achieved.Therefore,in order to explore the feasibility of high-percentage WMRA technology,systematic and in-depth theoretical and experimental studies were carried out.The paper involves the following specific contents:(1)In this paper,two types of warm mix additives which were made of synthesize wax and surfactant were employed.The artificial ageing asphalt was recycled,which was used to blend 15 kinds of WMRA binders containing 5 different percentages ranging from 30%to 70%.The experimental study was conducted on the high,medium and low temperature performance of WMRA binders.Meanwhile the changing trend between the performance of WMRA and different contents of ageing asphalt was analyzed.The objective was to study the performance of high-percentage WMRA technology primarily.(2)This paper further studied the rheological properties of the high-percentage WMRA binders and the combined effects of the warm mix additives and ageing asphalt.The rheological properties analysis was as follows:temperature sensibility,the complex shear modulus and phase angle master curves by frequency sweep tests,low-temperature creep compliance master curves,high-temperature creep properties,and fatigue properties.The results indicated that the two types of warm mix additives could enhance the low-temperature creep and fatigue resistance performance of recycled asphalt.The R warm mix additive composed of synthetic wax could reduce the asphalt viscosity and improve the low-temperature properties more significantly while the surfactant M contributed more to the high-temperature properties.With the combined effects of warm mix additives,ageing asphalt and virgin asphalt,it was found that the fatigue resistance performance of high-percentage WMRA binders was improved considerably compared with 90#virgin asphalt,indicating that the durability was satisfactory.(3)Based on the evaluation of macro-performance,microstructures and properties of high-percentage WMRA were studied.Fourier transform infrared spectroscopy(FTIR),gel permeation chromatography(GPC)and differential scanning calorimetry(DSC)were utilized to discuss the ageing and recycling mechanism of asphalt as well as the warm-mix mechanism of different kinds of warm mix additives.Meanwhile,the changing trends of the microstructures,thermal properties,molecular weight and its distribution of recycled asphalt binders before and after ageing were analyzed quantitatively.The relationship between micro-performance and thermal properties and the macro-performance was analyzed in order to establish the foundation for the further mechanism and microscopic performance research of WMRA technology.(4)According to the evaluation and analysis of asphalt properties,the paper also evaluated the pavement performance of high-percentage WMRA mixture.Two percentages(50%and 70%)of RAP,which was from the top and the bottom layer with different gradations of aggregate,were recycled by using two types of warm mix additives.The RAP was divided into three sizes and the portion less than particle diameter of 1.18mm was removed.Thus the void structure of mixture was optimized.The mixing and compaction temperature of WMRA mixtures containing different percentages of RAP was determined repectively.Furthermore,the optimum asphalt content was also confirmed for each recycled mixture.As a result,the mix design method suited for the high-percentage WMRA mixture was improved.Then the high-temperature stability,moisture susceptibility,low-temperature crack resistance and fatigue properties of high-percentage WMRA mixtures were analyzed by a series of pavement performance tests.Moreover,the consistency analysis of the high,medium and low-temperature properties of the recycled asphaly binders and mixtures was carried out.It could be concluded from the results that the high-percentage WMRA mixtures could satisfy the requirements of asphalt pavement performance while the low-temperature performance and moisture susceptibility would be the focus of future research.The performance of WMRA binders can predict the changing trend of mixture performance well and there was a good relationship between them. |
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