Experimental And Computational Investigation Of The Interface Shear Bonding Performance Between Asphalt Pavement Layers

Asphalt pavement consists of several structural layers with different material properties which are bonded together to form a monolithic structure and withstand under traffic loading and environmental circumstances.Consequently,bonding conditions between adjacent layers could play an essential role in the performance of the asphalt pavement structure.Having recognized the fact,this dissertation aims to research the shear bonding behavior of interface between asphalt layers.To fulfill this objective,an experimental and analytical approach was adopted to evaluate interfacial bonding performance between asphalt layers.First,it was found that in the absence of an international standard protocol for evaluating interface bonding,it is inevitable that testing results are not comparable in all cases.In addition,previous studies revealed that parameters such as temperature,loading conditions,materials and so on have significant effects on interface behavior.For this reason,as part of this dissertation,important features of a standard test method that should be taken into consideration were demonstrated,and a framework for a systematic approach to the proper evaluation of interface bonding was presented.Second,an experimental campaign in the laboratory was carried out to evaluate interfacial bonding performance between asphalt layers.In the first phase,monotonic interface shear tests were performed using a direct shear test apparatus where both normal and shear stresses are applied to the layer interface.Influential parameters such as temperature,vertical pressure,and tack coat application rate were considered to analyze the influence of each parameter on interface shear strength.Then,statistical analysis was employed to determine the significance level of each factor on interface shear strength.In the second phase,laboratory fatigue tests were performed to assess interface fatigue behavior.The tests were carried out with a new developed 4-point shear test(4PST)set-up which can also apply normal pressure to the specimens.The combined effect of temperature,normal pressure,loading frequency,and shear stress with single tack coat type and application rate were considered for evaluation.Two interface failure criteria were applied,the effect of each parameter on the interface fatigue life and shear stiffness were assessed,and corresponding fatigue laws were established accordingly.Then,the significance of each factor on the fatigue properties of the interface was determined using statistical analysis.Third,a numerical analysis modeling was conducted to assess the effect of shear stresses on asphalt pavement performance under repeated loading conditions and evaluate the potential of shear failure at the layer interface.A three-dimensional(3D)finite element(FE)model was developed to calculate the stress state within the asphalt pavement.Five different cases of vehicle maneuvering where shear forces acting on the surface layer were selected and pavement responses were obtained and analyzed under 100 loading cycles at three different temperatures.The relationship between normal and shear stresses was investigated,and a shear failure criterion was introduced to examine the possibility of debonding at the layer interface.Findings of this research showed that further studies are needed to establish a robust standard procedure so that it can be efficiently utilized for interface bond assessment in pavements.Monotonic shear test results indicated that all experimental parameters exerted a significant influence on interface shear strength.Among which,the temperature had the most significant effect followed by normal pressure and tack coat application rate statistically.Moreover,regression models developed for predicting interface shear strength were consistent with measured data.Experimental fatigue tests demonstrated that two interface failure criteria were successfully adopted in this study.Furthermore,all parameters had an impact on interface fatigue parameters.Power fatigue laws with a high coefficient of determination were also established to correlate interface fatigue life with shear stress for each temperature.A multiple regression model was developed successfully to predict the initial shear stiffness.All in all,the new four-point shear set-up successfully evaluated the interface fatigue performance in shear mode and could have promising results in future applications.The numerical analysis revealed that pavement responses at structural layer were larger than their counterparts at the layer interface.With increasing temperature,the pavement responses increased for all studied cases accordingly.Finally,the concept of interface shear ratio(ISR)was presented to evaluate the potential of debonding at the layer interface.According to initial results,the ISR could be considered as a promising criterion for assessing shear failure potential in layer interface.