| There is a technical difficulty that emerging reflective cracking easily when to beused for asphalt pavement with semi-rigid base course and asphalt overlay on oldcement concrete pavement. For this reason, it is a common approach in theengineering to set a stress absorbing membrane interlayer to prevent or abase thegeneration and development of reflective cracking. There are many forms of stressabsorbing membrane interlayer at present, such as Strata stress absorbing layer (SAL),Geotextiles and rubber asphalt SAL. The designing and comprehensive roadperformance of rubber asphalt mixture (RAM) with extra large asphalt-aggregate ratio(AAR) was studied in this paper. Meanwhile, the feasibility of RAM with extra largeAAR used both to be structural layer of pavement and SAL was studied and discussed.The research was mainly carried out from the following several aspects:First of all, the preparation process of rubber-asphalt was studied. The propertiesof rubber-asphalt affect the performance of mixture directly. Therefore, through thepreparation in this study, there are several key points needing to pay attention in theprocess. The temperature, time and rotate speed of stirring are included. At the sametime, the compatibility of base asphalt and crumb rubber is also need to pay attention.Then, the mix design of skeleton structure RAM with extra large AAR waspreceded. There are some differences on mix design with the common design methodwhich determine the mineral aggregates first and then define the optimum asphaltcontent in this paper. The design method adopted in this paper was ascertain a rangeof asphalt content according to the engineering practice at first (7AAR was selected,the largest AAR is12.4%), then mineral aggregates gradation were designed to eachAAR respectively. In order to ensure the skeleton dense structure of mixture, thedesign method for mineral aggregates was the combination of coarse aggregate voidsfilling method (CAVF) and stone asphalt concrete method (SAC). The mixturedesigned with this method has the feature that the coarse aggregate form thestone-on-stone contact and the fine aggregate, filler and asphalt binder filling the voidof coarse aggregate. Thirdly, a serious of performance tests of asphalt mixture of each AAR in theroom was carried out. Marshall Stability test, wheel tracking test, SubmergedMarshall Stability test, freezing and thawing test, beam bending test, prismaticuniaxial compression test and fatigue test were included to evaluate the hightemperature stability, moisture susceptibility, anti-cracking property at lowtemperature and anti-fatigue performance of the mixture.At last, several technical indicators of skeleton structural RAM with extra largeAAR, the appropriate range of asphalt content and gradation were proposed accordingto test results of the mixture. At the same time, the social and economic benefits ofthis kind of mixture to be the undercourse of asphalt pavement were analyzed briefly.Test results showed that the RAM with extra large AAR designed with themethod of combination of CAVF and SAC could ensure the stone-on-stone contact ofthe mixture. And the mixture had favourable pavement performance. Especially on thehigh temperature stability, the dynamic stability was2530passes/mm when the AARreached12.4%. Meanwhile, there was also nice deformability for it. Theflexural-tensile strain at-10℃reached3000~5000με. Furthermore, the skeletonstructural RAM with extra large AAR used in the asphalt pavement is not only to be astructural layer, but can also to be a SAL and waterproof layer. Using this approach inthe engineering omitted the step of setting up a SAL single-handed and simplified theconstruction technology. It brought convenient for further engineering construction,saved the cost and improved the social and economic benefits compared with settingup a SAL specially. |
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