| With the advancement of highway engineering construction in China,highway construction projects at this stage are mainly concentrated in the underdeveloped areas with significant climate differences.In order to meet the road performance of asphalt pavement in these areas,high-performance modified asphalt is often needed,and SBS modified asphalt of good high and low temperature performance is widely used in these areas.Due to the short allowable construction season in these areas,low-temperature construction conditions cannot be avoided in the construction process of SBS modified asphalt pavement but will seriously affect the quality of pavement construction.Improper construction quality control of low-temperature pavement will often lead to asphalt aging,temperature segregation,insufficient compaction and poor adhesion between layers,which will lead to block cracks,longitudinal cracks and transverse cracks,ruts,wave entrapment,potholes and looseness at the early stage of pavement.However,ruts,longitudinal and transverse cracks often appear in large numbers only3～5 years after opening to traffic.In order to control the quality of low-temperature construction pavement,this paper determines the evaluation index of low-temperature pavement construction quality in the completion acceptance period.The indexes are divided into two levels.The first level include the representative value of road compaction and the pass rate of compaction.The second level indexes include the degree of temperature segregation,the shear strength between layers,the depth index of compacted ruts and the equivalent area of transverse cracks at construction joints.This paper studies on the construction temperature control of SBS modified asphalt,so as to determine the reasonable mixing,paving and forming temperature during the construction of SBS modified asphalt,which can effectively improve the quality of low-temperature construction pavement.1.Mixing temperature.The tentative mixing temperature of SBS modified asphalt is determined by workability test.Due to the high requirements of low-temperature construction conditions for the control of construction temperature,reasonable mixing temperature can not only fully combine the cement and the mineral,but also provide temperature guarantee for the subsequent paving and compaction links.Therefore,it is necessary to modify the upper limit of mixing temperature to make it suitable for low temperature construction.The results of the short-term aging test of SBS modified asphalt carried out during the construction show that 180℃ is the upper limit of mixing temperature.Based on the attenuation model of mixture transportation temperature,the lower limit of mixing temperature is 170℃.2.Molding temperature.The narrow molding temperature range determined by the workability test is not conducive to guiding construction.The relationship between the volume,high and low temperature performance and mechanical performance of the mixture and the temperature is analyzed through the Marshall forming test and the wheel rolling forming test with the initial pressure temperature controlled at low temperature,so as to determine the reasonable initial pressure temperature range of the mixture at low temperature,and determine the minimum allowable surface temperature after forming,which is verified by the rotary compaction test.The results show that the initial pressure temperature range is from 150℃ to 170℃,and the forming surface temperature should be higher than 115℃.3.Paving temperature.In order to deal with the influence of low temperature construction,this paper divides the paving temperature into the temperature of the underlying layer and the temperature of the mixture.The reasonable temperature of the underlying layer determined by the interlayer bonding performance is(40±10)℃through the interlayer bonding performance.Based on the transient simulation of the paving temperature attenuation model of ANSYS fluent,the paving temperature of SBS modified asphalt mixture is 170℃. |
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