| Asphalt pavement recycling technology can not only solve the problem of nowhere to pile up waste and pollute the environment,but also save costs and create huge economic benefits.Therefore,this technology is getting more and more attention in highway renovation and construction.However,the incorporation of a large number of reclaimed asphalt pavement(RAP)directly reduces the low temperature crack resistance of the recycled material.At the same time,due to the influence of external factors such as geographical environment and traffic load,quality problems frequently occur in the later service process of the road,which cannot meet the expected design requirements.This has become the key reason that restricts the use of high dosage of RAP.Therefore,it is very important to study the low-temperature anti-cracking performance of recycled asphalt mixtures.In this regard,this article starts from the two perspectives of materials and environment,based on the six kinds of RAP content(0%,10%,20%,30%,40%,50%),based on the natural environment of eastern coastal areas of China,-15℃ was used as the test temperature.To simulate the erosion of asphalt pavement under salty and wet environment,the specimens were subjected to salt erosion in three kinds of solutions(0%,10%and 20%)for 30 cycles;In order to study the influence of different types of cracks on the low-temperature anti-cracking performance of specimens,Ⅰ type cracks(incision located at the bottom center of the specimen)and Ⅰ+Ⅱ type composite cracks(incision offset bottom center 10mm and 20mm)were designed;At the same time,three loading rates(2mm/min,5mm/min,10mm/min)were also designed to study the failure modes of the specimens under different loading rates.In addition,in order to evaluate the rationality of low temperature crack resistance of reclaimed asphalt mixture,fracture energy(Gf)and cohesive force c were used as the indexes to evaluate Ⅰ type crack,and peak load(PMax)and fracture deformation(δFmax)were used as the indexes to evaluateⅠ+Ⅱ type composite crack.Through the comparative analysis of multiple indexes,the understanding of the damage mechanism of reclaimed asphalt mixture under low temperature environment is enriched,which provides a theoretical reference for evaluating the anti-crack performance of reclaimed asphalt mixture at low temperature.The following conclusions are obtained through SCB test,SEM test and data processing analysis.(1)This paper sets up two processes to regenerate asphalt.According to three indicators and SEM test,different regeneration processes have a great influence on the fusion effect of new and old asphalt.In addition,the pretreatment of extracted old materials can effectively improve the stability of the gradation of recycled asphalt mixtures.(2)The Gf of specimens decreased with the increase of RAP content and salt concentration,and increased with the increase of loading rate.(3)When RAP content reaches 40%,due to the larger viscosity of old asphalt,the strong action interface can improve the salt erosion resistance of reclaimed asphalt mixture.(4)By establishing the relationship between Mohr-Coulomb’s law and ultimate tensile stress,the evaluation index cohesive force c is obtained,which can effectively evaluate the influence of chloride salt concentration and loading rate on recycled asphalt mixture.(5)The cohesive force c decreases with the increase of salt concentration,and increases with the increase of loading rate.After being eroded by 20%chloride concentration for 30 cycles,the cohesive force curve of the specimen under each loading rate has little fluctuation range,indicating that the change trend of the low temperature crack resistance of the reclaimed asphalt mixture after being eroded by high concentration chloride salt is relatively stable.With the increase of RAP content,the cohesive force c is affected by many factors and fluctuates greatly.(6)At-15℃,when the loading rate of 2mm/min is used,the crack is basically destroyed along the asphalt mortar and asphalt fine material combination,while when the loading rate of 10mm/min is used,coarse aggregates are mostly damaged on the fracture surface of the specimen.(7)Under Ⅰ+Ⅱ type compound crack,the PMax of the specimen with the incision offset by 10mm from the bottom center is larger than that of the specimen with the incision offset by 20mm from the bottom center.The position of the incision offset from the bottom center only affects the area of the tension zone at the tip of the slit.(8)PMax increases with the increase of loading rate and RAP content,and decreases with the increase of salt concentration.When the RAP content reaches 30%or above,PMax fluctuates.(9)The δFmax of the specimen decreases with the increase of loading rate,salt concentration and RAP content,but when the salt concentration reaches a certain limit,the δFmax of the specimen will be in a stable state.(10)When evaluating the low-temperature crack resistance of recycled asphalt mixtures,it is considered that the performance of recycled materials fluctuates with the increase of RAP content,which affects the stability of PMax.Therefore,Gf should be the main evaluation indicator,combined with a comprehensive analysis of multiple indicators.In actual engineering application,it is recommended that the RAP content should not exceed 30%.Figure[37]Table[29]Reference[80]... |
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