Pavement Performance Of Crack Attenuating Mixture Ultra-thin Asphalt Overlay

The ultrathin overlay is used to be placed on the existing asphalt and concretepavement, and reflective crack is one of the most common distresses. Cracks not onlyreduce the vehicle comfort and safety but also accelerate the destruction of pavementstructure due to water penetration. In order to rehabilitate the pavement performance,there are five accesses to delay the occurrence and development of reflective crackingoverlay from five aspects:(1) Modify existing PCC surface.(2) Overlay layer/mixturemodification.(3) Cushion layers.(4) Reinforcement of HMA overlays.(5) Crackcontrol method. This paper mainly introduced the CAM (crack attenuating mixture)ultrathin overlay from prospective of anti-reflect cracking which was developed bythe Texas Transportation Institute (TTI). The cracking attenuating of ultrathin overlayis a hot mixed asphalt pavement layer less than or equal to2.5mm which can be usedas upper layer of pavement on highway or preventive treatment on existing pavement.This paper deliberated on verifying the pavement performance of the CAMultrathin overlay based on previous research. At first, the Bailey method was adoptedto analyze the maximum nominal diameter of4.75mm CAM and comprehend thecharacter of CAM gradation. Second, the performance of tuffs, Esso A70#asphalt andchloroprene rubber modified asphalt was verified and Marshall Method was used tofound out the optimum asphalt content of every gradation. Then determining the bestgradation and asphalt content accordingly and checking out its pavement performancecompliance with regulatory requirements was done. Third, a set of fixture wasdesigned and the gradation was chosen to discuss the relationship between themixture’s anti-cracking performance and asphalt content and chloroprene rubbermodified asphalt content. The experimental results demonstrated that the crack stressof modified asphalt mixture was improved22.4%than ordinary asphalt mixture.Eventually, this paper introduced how to deal with existing cement concrete pavementand the CAM ultrathin overlay construction process. The experimental results showed that the crack attenuating mixture had greatanti-cracking performance, especially with neoprene modifier of asphalt mixture.And the direct tensile test can be applied on MTS with the overlay tester fixture.