Research On Experiment And Model Of Interlaminar State Parameters Of Pavement Materials

According to related investigation of pavement diseases,many damages occur at the bonding of asphalt surface layer and base course.The poor state between layers not only leads to the diseases such as sliding cracks,pushing and swelling failure,but also affects the service life of pavement structure.The design method of asphalt pavement in our country is based on the theory of elastic layered continuous system,the interface between layers are not completely continuous,however.If the mechanical responses obtained from the continuous system are used to guide the design of pavement structure,the actual service life of pavement must be different from the design expectation.Thus,the author takes the interface between Sup-25 asphalt underlayer and cement stabilized macadam base as the research object.With the help of customized shear fixture,direct shear tests are carried out under different temperatures,immersion days and repeated shear load times so as to obtain the variation laws of interlaminar shear strength and bond coefficient.The results show that the interlaminar shear strength and bond coefficient decrease with the increase of temperature,immersion days and repeated shear load times;The interlaminar shear strength at 40℃ is only 35% of that at 0℃;The range of shear strength attenuation caused by water immersion is about 7.6%～32.6%;The residual shear strength is only 54% of that without damage after 4000 times of repeated loading.It is suggested that the necessary measures such as increasing the thickness of the asphalt surface layer,selecting reasonable interlaminar bonding materials,timely maintenance of the pavement,improving the construction quality of the pavement and limiting maximum axle load should be taken to weaken the adverse effects of external factors on the interlaminar state of the base course and surface course.Then,the CZM parameters are obtained by fitting the test data to establish the ABAQUS analysis model which reflects the real state between pavement layers.By comparing the continuous model,smooth model and contact model,the variation laws of different mechanical responses with the interlaminar state are obtained.The results show that the change of interlaminar state between the asphalt surface layer and base course changes the distribution of stress and strain in the pavement structure.With the deterioration of interlaminar state,the mechanical responses of asphalt pavement such as design indexes,rebound deflection and bottom shear stress increase gradually.The most unfavorable design indexes considering interlaminar state are the bottom tensile strain of asphalt layer and bottom tensile stress of base course;Compared with the continuous state,the bottom tensile strain of asphalt underlayer increases by 5.4 times and the bottom tensile stress of base course increases by 32% in the smooth state.It is suggested that the allowable interlaminar shear stress design index should be introduced to control the interlaminar shear fatigue failure,and the “intermediate state” beween well-bonded state and completely smooth state should be selected as the design interlaminar state,in which the fatigue cracking checking calculation can be carried out.The research results of this paper can not only help to better understand the influence of interlaminar state on pavement structure,but also establish the corresponding relationship between indoor test and calculation model and propose the improvement suggestions considering interlaminar state based on the elastic layered system theory,which can provide reference for the research of pavement interlaminar state as well as for the design and construction of asphalt pavement.