Study On The Technology Performance Of Asphalt Pavement Layer Interfaces

The quality of layer interfaces is one of the important factors that influence the life of the asphalt pavement. A poor bond between pavement layers destroys the unity of pavement structure and reduces its bearing capacity. Slippage failure often occurring at the places where vehicles accelerate or decelerate, is the most commonly observed problem related to poor bond between layers. The typical distress is described as crescent cracking. In order to achieve the desired bearing capacity and a longer lifetime of a pavement structure, the research on the technology of adhesion at the interface between asphalt pavement layers is of great significance.Based on the current technology of asphalt pavement layer interfaces, the paper analyzed the mechanical response of pavement structure with different bond conditions between pavement layers. The results showed the mechanism of U-shaped cracking and evaluated the influence of different bond conditions between pavement layers on asphalt pavement performance. Then through comprehensive laboratory experiments, this paper mainly studied the properties of the tack coat, seal coat, prime coat in the asphalt pavement structure. The bond strength of the interfaces was systematically evaluated by direct shear test and direct pull-off test, aiming to analyze the influence of several factors on the adhesive bond at the interface between pavement layers. Each statistically significant level was also tested in this paper. The feasibility of test methods and the reasonableness of evaluation indexes were validated through laboratory experiments, so as to provide a basis for revising related technical specification. At the same time, the shear fatigue properties at the interface of asphalt pavement layers were studied. The discussion about fatigue failure mechanism of the interfaces was conducted. A model was put forward and three parameters were selected to characterize shear fatigue failure at the interface. Finally, on the base of mechanical analysis and testing research, the design method of the asphalt pavement, considering shear-resisting strength, was put forward.The details of the research can be described as follows:(1) For the semi-rigid base asphalt pavement, by inputting the test parameters into a finite element program (ABAQUS), the paper studied the influences of horizontal loads, bond conditions between pavement layers and overloading of vehicles on the pavement structure mechanical response and analyzed the causes of the U-shaped cracking. The results showed that horizontal loads had a significant influence on stress distribution of pavement structure, especially for top surface layer. The vehicle overloads and the discontinuation between the surface and the base exacerbated the rut of the asphalt pavement. For the longitudinal slipping, its occurring was mainly caused by overloading of vehicles, and then by the discontinuation between the surface layers. For the deflection, the greatest effect factor was the load, the next was the bond condition between the surface and base layers, and the last one was the bond condition between the surface layers. The bottom of U-shaped cracking was open tension-type cracking led by tensile stress while the both sides of U-shaped cracking were shear-type cracking led by vertical shear stress. The continuity of surface course interlayer and horizontal loads had a great effect on the development of U-shaped cracking.(2) This paper investigated the influence of several factors on the adhesive bond provided by the tack coat at the interface between pavement layers. These factors included application rate, tack coat type, testing temperature, the surface cleanliness, moisture, sudden change of environment, traffic and mixture type. The statistical significance of the differences in interface bond strength was evaluated. Emulsified asphalt, the polymer modified emulsion asphalt and hot asphalt binder were selected as the tack coat materials. At the same time, the influence of different bond conditions between pavement layers on pavement high temperature performance and durability was evaluated. The results showed that the optimum application at the test temperature of 60℃was 0.1～0.2kg/m~2 less than the application at that of 25℃Tack coat was good for improving interlayer shear performance, high-temperature stability and durablity of the asphalt pavement, and reducing the unfavorable effect of interlayer pollution, rain and environment change. Lastly, this paper recomended suitable tack coat materials and application rates for different climate conditions. On the base of mechanical analysis and testing research, the evaluation method, evaluation index and the technical requirements for the anti-shearing performance of asphalt pavement structure were put forward.(3) For the technology of synchronous surface dressing, the effect factors of the interface shear strength were examined and the statistical significance of the differences in interface shear strength was evaluated. The comparison on the interface shear strength and permeability between synchronous surface dressing and slurry seal was made. The results showed that asphalt properties, aggregate lithological composition, processing mode, and the asphalt binder and aggregate spreading synchronization provided a significantly better bond at the interface between the pavement layers, while the aggregate particles size did not significantly affect the bond strength at the interlayer. As seal course use, the shearing strength of slurry seal was smaller than that of the synchronous surface dressing, but its waterproof performance was obviously better than that of the synchronous surface. Lastly, the paper recommended the suitable seal coat materials for different rainfall and mixture types.(4) The experiment included three types of prime coat materials (cutback, emulsified asphalt and the polymer modified emulsion asphalt) and two types of semi-rigid base materials (cement stabilized granular base and lime-flyash stabilized granular base). The influence of different dilution ratio, prime coat type, base type and curing time of semi-rigid base on penetrability was evaluated. The results showed that the permeability of the cutback asphalt was far better than that of the emulsion asphalt while the polymer modified emulsion asphalt was unsuitable to be used as the prime coat. At the same application rate, the penetrability of prime coat on the cement stabilized granular base was better than lime-flyash stabilized granular base, and the application rate on the lime-flyash stabilized granular base was smaller than on the cement stabilized granular base. The spraying occasion of the prime coat was good for early. Lastly, the paper recommended the suitable prime coat materials for different bases.(5) A shearing test method was developed to conduct the interlayer shearing-fatigue test. The paper studied the effects of existence of tack coat, tack coat type and the surface cleanliness on the shear fatigue property. By analysis, the paper put forward evaluating method, evaluating indexes and a simple shear mechanical model for interlayer to assess the shear fatigue properties of the interlayer between the pavement layers. Based on the analysis of the mechanism of shear fatigue failure, a simple performance declination model for interface was put forward.(6) According to the climatic characteristics of our country and the performance requirements of interlayer materials, the average highest temperature in July and rainfall were selected as the climatic zoning indexes of asphalt pavement interlayer materials. Based on mechanical analysis and testing research, the paper put forward a calculation method of interlayer allowable shear stress and the design method of asphalt pavement considering shear strength.