Study On The Optimal Secondary Compaction Time Of Emulsified Asphalt Cold Reclaimed Asphalt Mixture

At present,China’s road has entered the maintenance stage,in order to recycle the waste asphalt mixture,plant mixing cooling regeneration technology arises at the historic moment.After the construction of the cold regenerated layer,the hot mix asphalt mixture can not be spread immediately,so it is necessary to keep the cold regenerated layer healthy.The specification requires that the treatment should not be less than 7 days before the next layer of spreading,therefore,the time needed from spreading the cold regeneration layer to spreading the hot mix asphalt mixture is called the secondary compaction time(curing time).However,some research data show that reducing the treatment time is beneficial to improve the strength of cold regenerated layer.This paper studies the influence of secondary compaction time on the performance of cold regenerated layer,and analyzes the factors that influence the secondary compaction time(health preservation time),so as to provide some reference value for the field construction of cold regenerated layer.Firstly,three types of emulsifier,LBP1,CP and R3T1,were used to prepare emulsified asphalt.In the process of preparing emulsified asphalt,the content of emulsifier and the p H value of emulsifier soap liquid affect the performance of evaporated residual asphalt.The penetration degree,softening point,5 ℃ ductility and storage stability of evaporated residual asphalt were tested.Determine the optimum dosage of emulsifier.Secondly,in order to verify the existence of the optimal secondary compaction time for cold regeneration,RAP,LBP1 and CP emulsified asphalt from a mixing station in Chongqing and a mixing station in Guiyang were selected for tests.According to the splitting strength at 15℃,the splitting strength at 24 h and the void fraction of the four emulsified asphalt cold recycled mixtures under different secondary compaction times,it can be concluded that the optimal secondary compaction time of the two kinds of RAP is less than the seventh day required by the code.Thirdly,the influence of different emulsified asphalt,cement,early strength agent,retarder and water content on the optimal secondary compaction time is analyzed.Three kinds of emulsified asphalt and one kind of RAP were selected to study the optimal secondary compaction time for cold regeneration.According to the splitting strength at15 ℃,the splitting strength ratio and the voidage after 24 h immersion,it can be concluded that the demulsifying speed of emulsified asphalt has some influence on the optimal secondary compaction time,and the faster demulsifying speed can reduce the optimal secondary compaction time.Through analyzing the influence of three types of cement on the optimal secondary compaction time,the test results show that: the cement hydration reaction speed is fast,the optimal secondary compaction time is short;The effects of the early strength agent and retarder on the optimal secondary compaction time were analyzed.Results showed that the early strength agent shortened the optimal secondary compaction time,and the retarder prolonged the optimal secondary compaction time.Finally,the influence of water content on strength was verified.The experimental results show that the longer the sealing time is,the lower the strength of emulsified asphalt mixture will be,so it can be concluded that the moisture content will prolong the optimal secondary compaction time.Finally,by comparing the difference of cold regeneration road performance between the 7-day health treatment time stipulated in the specification and the optimal secondary compaction time determined in this paper,the results show that;Compared with the 7-day treatment time,the stability of cold regeneration,freeze-thaw splitting,dynamic stability and low temperature cracking resistance are increased by 28%,16%,26% and 37% respectively under the optimal compaction time,and the road performance is significantly improved.