Research On Meso-Scale Numerical Simulation Of Cement Treated Base Material Semi-Circular Bending Cracking Based On Cohesive Zone Model

Cement treated base(CTB)is the main form of asphalt pavement base in China,and a large number of road bases have suffered fatigue damage during long-term service.For the preservation of semi-rigid base structures,it is necessary to study the damage cracking behavior of CTB material.Currently,the cracking research concentrates on experimental methods,and most theories are based on the assumption of homogeneity and rarely involve the heterogenous characteristics.However,CTB material is a multi-phase material composed of aggregate,cement mortar,voids and interface transitional zones(ITZ),and it is unable to deeply study the relationship between its microstructure and macroscopic mechanical properties by means of traditional fracture mechanics theory.Therefore,it is necessary to establish meso-scale cracking model of CTB material to study its fracture behavior.Firstly,heterogeneous meso-fracture model was studied.Elliptical and polygonal random aggregate digital specimens were generated according to two methods respectively,which can characterize the gradation,content,maximum size,shape of aggregate and porosity,size,shape of voids.A minimum rectangle area method was developed to calculate the polygon aggregate size,and a buffer zone method was proposed to determine the minimum distance between randomly generated polygon aggregates.The zero-thickness cohesive elements were inserted into model to achieve cracking propagation with cohesive embedding algorithm based on cohesive zone model(CZM).Spatially-varying Weibull random fields were given to the mortar and interface transition zone to characterize the heterogeneous fracture properties of CTB material.Secondly,finite element model(FEM)was established by means of ABAQUS.Two nonlinear solving algorithms provided by ABAQUS were analyzed and compared,and the result shows that ABAQUS/Explicit is suitable for the quasi-static problem in this paper.Convergence analyses of grid density and loading time were carried out,and grid density was determined to unit size L=2.0mm and loading time was determined to 0.5s with respect to loading displacement 3.0mm.Thirdly,meso-scale parameter of CZM were studied.Nano-indentation tests were employed to obtain the modulus of aggregate and mortar,74.6GPa and 30 GPa respectively.Based on digital image processing(DIP)technology,two-dimensional reconstruction of the SCB core sample was realized,and the meso-fracture model based on the actual aggregate was established.Inverse analysis was carried out to determine the rest of CZM parameters,and Weibull random fields were given to cohesive elements to characterize its heterogeneous fracture properties.Finally,virtual fracture tests of semi-circular bending(SCB)test were carried out based on meso-fracture model.The reliability and applicability of the model were checked,and parameter sensitivity analyses of aggregate properties(aggregate gradation,content,maximum size and shape),ITZ properties,void properties(porosity,void size and void shape)and inhomogeneity properties were carried out to study the influence of meso-structure characteristics on the crack-resistance and reveal the meso-mechanism of its macro-fracture behavior.