Study On Anti-cracking Performance Of High-Flexible SBS Modified Asphalt And Its Mixture In High Altitude Area

The low temperature,UV aging and temperature difference in Tibet are strong,which require high resistance to low temperature cracking,fatigue and aging of asphalt materials.Therefore,to improve the performance of the commonly used asphalt in Tibet,and study the rheological properties,modification mechanism,road performance and durability of the asphalt mixture,as well as the application in the crack resistance structure of the asphalt pavement in Tibet has far-reaching significance for the long life of the asphalt pavement.Cluster analysis was used to divide regions with the same climate characteristics in Tibet and analyze the correlation with the characteristics of road surface diseases in the region.The results show that Tibet can be divided into five regions from I to V based on climate clustering.The annual mean minimum temperature and annual mean precipitation have significant elevation sensitivity,while the annual mean maximum temperature has no significant elevation sensitivity.The main diseases of asphalt pavement are transverse and longitudinal cracks caused by low temperature or large temperature difference and loose pits caused by freeze-thaw cycle.Dynamic shear rheological test and low temperature creep test were used to compare the properties of commonly used asphalt in Tibet and analyze its applicability in five regions of Tibet I～V.The results show that the high-temperature performance of direct-casting SBS and finished-product SBS is better than that of SBR,but the low temperature performance of SBR is better than that of direct-casting SBS and finishedproduct SBS.The fatigue resistance of direct-casting SBS and finished-product SBS is obviously better than that of SBR under medium and high temperature conditions,but high temperature has the greatest influence on SBR,and direct-casting SBS is obviously better than that of finished-product SBS.Compared with finished-product SBS,direct-casting SBS improved the low temperature performance to a certain extent,but did not significantly improve the high temperature performance.90#A grade ordinary asphalt is not suitable for use in Tibet.Direct-casting SBS,finished-product SBS and SBR are only applicable to Tibet region III～V,and the recommended priority order is direct-casting SBS,finished-product SBS and SBR.The performance of SBS modified asphalt was improved by self-developed high flexibility modifier,and viscoelastic,rheological and aging properties were studied by conventional test,dynamic shear rheological test and low temperature creep test.The results show that the high flexibility modifier can effectively improve the low temperature performance,fatigue resistance and UV aging resistance of SBS modified asphalt,but has a slight adverse effect on its high temperature performance.It can effectively reduce the viscosity of SBS modified asphalt,so that it has isothermal mixing characteristics of high temperature and low viscosity,low temperature and high viscosity.In Tibet region I and II,the recommended dosage range of highly flexible modifier is 8～10% and 6～10%,respectively.In Tibet region III～V,the recommended dosage range of highly flexible modifier is 6～8%.In order to further reveal the influence of highly flexible modifier on the microstructure of SBS modified asphalt and its modification mechanism,fluorescence microscopy,atomic force microscopy,infrared spectroscopy and thermal analysis were used to study the microstructure.The results show that the addition of high flexibility modifier can promote the uniform dispersion and swelling of SBS modifier molecules,and change the number and size of the original SBS modified asphalt bee structure,network crosslinking structure is strong,so as to improve the comprehensive performance of SBS modified asphalt.When the content of high flexibility modifier is 8%,the thermal stability of highly flexible SBS modified asphalt structure is the best and the mass loss is the least.The road performance and durability of SBS modified asphalt mixture were studied by using Marshall test,rutting test and fatigue test.The results show that the high flexibility modifier greatly improves the water damage resistance and low temperature bending resistance of SBS modified asphalt mixture.Although the high temperature rutting resistance decreases slightly,it still meets the requirements of the specification.Compared with the existing SBS and SBR modified asphalt mixture,the fatigue life of the asphalt mixture is about 20 times higher than that of the existing SBS and SBR modified asphalt mixture.Semi-circular bending SCB,low-temperature constraint stress TSRST Test and Texas Overlay Test were used to analyze the low-temperature crack resistance and anti-reflection crack performance of highly flexible SBS modified asphalt mixture,and ABAQUS finite element method was used to study the suitable layer and thickness of highly flexible SBS anti-crack functional layer.The results show that highly flexible SBS modified asphalt mixture has excellent low temperature crack resistance and anti-reflection crack performance,which can effectively offset the stress concentration and reduce the tensile strain and tensile stress at the bottom of asphalt surface layer.High flexibility SBS modified asphalt is not only suitable for each asphalt structural layer,but also as a crack prevention functional layer,the best suitable layer is the top surface of the base,and the best suitable thickness is 2cm.