Study On Mechanism Of Crumb Rubber Modified Asphalt

Crumb rubber modified asphalt can not only improve asphalt pavement performance, but also can achieve the waste re-use, further study on the crumb rubber modified asphalt isvery important.This paper is based on western transportation scientific and technological project "The applied research of crumb rubber modified asphalt ". Aimed at asphalt rubber mixture wet production process, using fluorescence microscope, infrared spectrum, differential scanning calorimeter modern analytical test methods, this paper went on a preliminary analysis in the composition or structure of asphalt and rubber, and then by analyzing the test results of asphalt,s conventional and SHRP performance tests. Influence of modification process, particle size, powder type, rubber content as well as the type of base asphalt on the performance of modified asphalt were investigated, based on this the modified mechanism of crumb rubber modified asphalt was summed up, This paper went on further analysis of the mechanism which crumb rubber palyed in asphalt mixture.Through analysis, the main conclusions are as follows: (1) The factors that influence the performance of crumb rubber modified asphalt are summed up to two types: one for factors of the processing technology (mixing temperature, mixing time), and the other for factors of the materials (powder type, particle size and the types of base asphalt). The test results of crumb rubber modified asphalt conventional and SHRP performance index show that, there is a inflection point on relationship map between mixing temperature, crumb rubber content and three conventional indexes of modified asphalt, mixing temperature and crumb rubber content have a reasonable scope; The performance of modified asphalt is of time-dependence, if mixing time is too long, the performance is degradate; Asphalt modified by crumb rubber of large size has beteer temperature sensitivity, high temperature and elastic performance, which has nearly equal effect in low temperature performance; The performance of modified asphalt of oblique crumb rubber is significantly better than meridian crumb rubber; Asphalt modified by base asphalt of high content light components, has bad temperature sensitivity and good low temperature performance; (2) Fluorescence microscope images show that crumb rubber has role of adsorption and filling. when mixing time is 60 min, oblique crumb rubber of small size or asphalt with high component, crumb rubber distribute more evenly and more easily absorb the light fraction and swelling. Differential scanning calorimeter(DSC) show that oblique crumb rubber of small size or asphalt with light component, its modified asphalt,s absorption of heat is lower, temperature sensitivity is higher. Infrared spectroscopy (IR) show that the interaction between crumb rubber and asphalt have chemical and physical modification. The differences in composition and structure between crumb rubber and asphalt, which can lead to performance differences in modified asphalt. (3)Through macro-and micro-analysis, in this study experimental conditions, the appropriate mixing temperature is about 180℃, mixing time is about 60min. oblique crumb rubber of large particle size is recommended, the content of crumb rubber is about 20%. Base asphalt is recommended to select targetly according to different characteristics of climate and traffic conditions; (4) Modified mechanism of crumb rubber modified asphalt can be explained as, crumb rubber absorb Light component of asphalt, and then their swelling happens, which form boundary layer and boundary transition layer. Micelle fill in the network structure of crumb rubber, which forms three-dimensional network structure, resulting in the improvement of asphalt,s performance; (5)Whether it is dry process or wet process, the role of crumb rubber played in asphalt mixture is divided into physical and chemical action, in this dual role, makes crumb rubber asphalt mixture to obtain a good pavement performance.