Study On Preparation And Properties Of Modified Asphalt Suitable For High Altitude Area

Compared with the eastern coastal areas,the asphalt pavement in the long-term use process is more vulnerable to low temperature cracking,while the ultraviolet effect intensifies the aging of asphalt,which shortens the service life of asphalt mixture.Therefore,the performance of asphalt mixtures in high altitude areas has put forward higher requirements.From the point of view of asphalt binder,a kind of composite modified asphalt with good low temperature performance and strong aging resistance was prepared to meet the application requirements of asphalt pavement in high altitude areas.(1)?The SBR and TPS modifiers and their adding sequence were determined by three main indexes and segregation indexes of Korean GS90 base asphalt.The optimum preparation process of composite modified asphalt was determined by orthogonal test,and then the optimum content of composite modified asphalt modifier was determined under the optimum preparation process.SBR/TPS composite modified asphalt was prepared.The preparation process is as follows: heating the base asphalt to 140 ?,adding 3% SBR and 6% TPS at the same time,stirring manually for 3 minutes,swelling for 30 minutes,raising the temperature to 165 ?,opening the high-speed shearing machine,shearing for 60 minutes at 5000r/min,developing for 35 minutes until the bubbles disappear completely at 140 ? after shearing.(2)?Korean GS90 base asphalt,SBS modified asphalt,SBR modified asphalt and SBR/TPS composite modified asphalt were selected.The aging asphalt was prepared by rotating film oven aging RTFOT,long-term pressure aging PAV and indoor simulated ultraviolet aging UV.The conventional and rheological properties of the four asphalts before and after aging were tested,and then the PG classification of asphalt was completed.By changing the aging order of PAV and UV,dynamic shear rheological test and trabecular bending test were used to further study the effect of interactive aging on the rheological properties of asphalt at high and low temperatures.The results show that the PG grading of GS90 base asphalt is 58-22,SBS modified asphalt is 70-22,SBR modified asphalt is 64-22,SBR modified asphalt is 70-28,and composite modified asphalt is 70-28.The high and low temperature grading of composite modified asphalt is the best.The aging degree of composite modified asphalt in the second way(aging order is ORIGINAL-RTFOT-UV-PAV)is stronger than that in the first way(aging orderis ORIGINAL-RTFOT-PAV-UV),and the short-term aging is better.After aging,asphalt is more sensitive to ultraviolet aging.After long-term pressure aging,the aging effect of ultraviolet aging on asphalt decreases.Considering the shortage of existing specifications for ultraviolet aging of asphalt,starting from the most disadvantageous principle of the test,it is recommended that the order of asphalt aging simulation test in high altitude areas is ORIGINAL-RTFOT-UV-PAV.(3)?The interaction mechanism between SBR,TPS and base asphalt and aging mechanism of modified asphalt were analyzed by fluorescence microscopy,infrared spectroscopy and differential scanning calorimetry.The results show that the modification of composite modified asphalt is the result of the interaction of asphalt,SBR and TPS.Its modification mechanism is the combination of chemical modification and physical modification.Composite modified asphalt has the lowest glass transition temperature and the best low temperature performance.Ultraviolet aging has the same effect as long-term pressure aging,and its aging mechanism for asphalt is different from long-term pressure aging.(4)?The AC-13 gradation commonly used in high altitude areas is selected for asphalt mixture mix design.The optimum asphalt dosage of three kinds of modified asphalt is determined.The pavement performance of the mixture is evaluated by high temperature rutting,low temperature trabecular bending,immersion Marshall and freeze-thaw splitting tests.The results show that the low temperature crack resistance of the composite modified asphalt is the best,and the high temperature stability and water stability meet the requirements of the specification.Generally speaking,the performance of composite modified asphalt mixture is more suitable for high altitude areas with harsh climate.