Study On Structure And Materials Of Asphalt Overlay For Old Cement Concrete Pavement In Hot And Humid Regions

Due to the advantages of its full use of the old concrete faceplate, reducing the pollutionof environment, saving resource and driving comfortably, etc, paving asphalt overlay hasalready been one of common technological measures in the reconstruction of old concretepavement. With the climate characteristics of damp, rainy, hot and summer lasting for a longtime on humid and hot regions, therefore, paving asphalt overlay over old concrete pavementwill meet with problems of water damage, rut, and so on, besides restraining the reflectioncracks on these areas.Based on the pavement diseases of concrete road and tracking observation data forsuccessive years about testing roads and entity engineering on hot and humid regions, thispaper made further thoroughly study of the asphalt overlay structures and materials of oldconcrete pavement on hot and humid regions, and obtained systematic conclusions.After the investigation and evaluation into the using status of semi-rigid base cementconcrete pavement on typical sections of humid and hot regions, analyzing the disease form,forming mechanism and the influencing factors, it was found that void under road surfaceplate was the typical disease type to semi-rigid base cement concrete pavement on theseregions. In order to avoid waste and occurring of unreasonable situation to local evaluationand full consideration vehicle operation characteristics, it was recommended that different oldcement concrete pavement driveway should take different pavement performance evaluationmethods.With the test of temperature field of asphalt overlay on old cement concrete pavement onhumid and hot areas, through the analysis of test results, it was found that the temperature ofthe place under road surface2cm was extremely high and extreme low both high-temperatureseason in summer and cold season in winter. According to a linear regression analysis ofresults, the estimate formula of highest temperature in the place under the surface2cm wasobtained, and the importance of factors affecting the highest temperature was analyzed byusing the gray relational analysis.The3-D finite element model was adopted to analyze the influence of axle load size,asphalt layer thickness and modulus, anti-cracking structure layer thickness and modulus and basic modulus on pavement structure stress rule under vehicle loading, temperature loadingand the coupling effects. After comprehensive account of the structure stress on the influenceof various structural layer parameters, the reasonable thickness of asphalt overlay and thereasonable thickness and modulus of anti-cracking structure layer were recommended basedon stress absorption interlayer and open-graded large stone asphalt mixes respectively,.The propagation path of reflection cracks on the asphalt overlay setting stress absorptioninterlayer and open-graded large stone asphalt mixes were simulated numerically. The resultsshowed that the extending path of reflection cracks began from the original cracks tips with alarger angle and extended gradually similar as the Chinese character “Zhi” until it reached thesurface layer, but the mechanism of anti-cracking was different.According to the hot and humid climate characteristic and the damage situation of oldcement concrete pavement, material composition and design methods and performanceinspection technology standards of the each layer of adding structure were proposed. Forstress absorption layer of adding structure, ensuring good quality of aggregates, polymermodified asphalt should be used, combining Superpave design theory with the mix proportiondesign, penetration test should be applied to test its high-temperature shear performance of themixture. According to the test results of direct tensile test, the low temperature anti-crackingperformance evaluation index was established. For open-graded large stone asphalt mixes, bigMarshall method on mixture proportion design should be adopted, and emphatically from thewater stability, the high temperature stability, water seeping three aspects to test itsperformance. In order to improve the asphalt overlay anti-rutting function, high modulus asasphalt mixture asphalt overlay below the surface should be adopted, uniaxial compressiontest method was used to test dynamic modulus of asphalt mixture, the influence of gradation,asphalt content, temperature on dynamic modulus was analyzed.In order to test the rationalityof adding structure, basing on stress absorption layer or open-graded large stone asphalt mixes,the fatigue test was developed. Through analyzing flexural-tensile and shear fatigue testresults, it was found that setting anti-cracking structure layer could obviously delayflexural-tensile and shear reflection crack formation.From the mechanism of typical failure modes of the hot and humid regions old asphaltcement concrete pavement structure, the material selection of each layer was discussed, and the right type of material was recommend. Through the analysis of extending mechanism ofthe old cement concrete pavement structure adding a anti-cracking layer, design index ofadding structure was raised, the detailed calculation method was discussed, and a detaileddesign process was recommend.