Mechanical Behaviour And Failure Mechanisms Of Asphalt-aggregate Systems Subjected To Direct Shear Loading

Asphalt mixture has been widely used in highways,airport and bridge pavement constructions.When the vehicles run on the asphalt pavements at a constant speed,the stress and the strain inside the structural interlayers have no obvious changes.However,several cases of slippage cracking and permanent deformation appear at the poor asphaltaggregate interface where the the shear stress exceeds the shear resistance of asphalt mixture.At present,the typical destruction in terms of rutting,peeling,and cracking are often reported,which seriously reduces road performance and service life.Therefore,much more understanding the mechanical characteristics and failure mechanisms of asphalt mixture is an indispensable and meaningful step for improving service life of asphalt pavement.This paper focuses on mechanical behavior,failure mechanisms,shear fracture energy and interface slip of asphalt-aggregate systems subjected to direct shear loading.The main details consist of the following parts: 1)introduce the current study of asphalt mixture and its interface;2)self-design direct shear test and obtain the single-peak curve(SPC)and the double-peak curve(DPC);3)analyze mechanical behavior of the SPC.s and the DPC.s;4)analyze the mechanisms of the SPC.s and the DPC.s;5)study the shear fracture energy and interface slip.Based on the analysis of experimental data,the main discussions and conclusions of this paper can be summarized as follows:Two kinds of the complete stress-displacement curves,including the single-peak curve(SPC)and the double-peak curve(DPC),are clearly observed.Each of the double-peak curves(DPC.s)generates two peak values with increasing shear displacement.The mechanical behavior of asphalt-aggregate systems can be governed by the characterizes of the stone surface,asphalt film thickness,loading rate,adhesion between asphalt and aggregate and other unknown factors.Especially,the loading rate has a pronounced effect on the shear strengths of the SPC,the first-peak stress and the second-peak stress of the DPC.It confirms that the potential failure modes of the DPC.s include adhesive failure at the asphalt-aggregate interface and cohesive failure within the asphalt film.Furthermore,stress concentration,shear flow,interface slip,viscosity and hysteresis of asphalt mastic might contribute to the delayed secondpeak curves of the DPC.s.For each experimental condition,it indicates that the singlepeak curves(SPC.s)tend to envelop the double-peak curves(DPC.s)and the values of shear fracture energy of the SPC.s are much higher than those of the DPC.s.Shear fracture energy of the asphalt-aggregate specimens was an integrated fracture energy of the adhesion and the cohesion;for the DPC.s,the adhesive energy tends to get a smaller percentage than the cohesive energy during the direct shear testing.The evolution of the cumulative dissipated fracture energy with the increasing corresponding displacement of the SPC.s and DPC.s clearly indicates that producing the SPC.s always consumes higher energy than producing the DPC.s during the direct shear testing for each experimental condition.The experimental results clearly show that the reduced fracture energy of the DPC.s is mainly due to the substantial apparent shear-dependent slip,including adhesive slip and cohesive slip that occur simultaneously and promote each other in the shear regime,which would be more likely to save the dissipated fracture energy than as expected with the SPC.s.This study suggests that fracture energy should be considered as a significant parameter in the failure and healing analysis of asphalt pavements.The fatigue life of asphalt pavement can be improved by enhancing the bonding between asphalt binders and aggregate.