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Semi-flexible pavement (SFP) material is a composite comprising cement, coarse aggregates and asphalt mortar, which has complex mechanical properties. Traditional experimental methods struggle to accurately quantify the effect of each phase and their interfaces on the SFP's mechanical properties. Micromechanical modelling based on finite element method offers a promising solution. In this study, a new micromechanical model for SFP is proposed, idealizing the material by representative volume elements. SFP mesostructure is represented as a simplified five element composite consisting of cement, asphalt mortar, aggregate, pore and cement-asphalt mortar interface. Periodic boundary conditions are used to simulate an infinite repetitive structure within a finite computational domain. The resulting model allows evaluating the stiffness and damage resistance of SFP in a computationally efficient manner. This model is utilized to explore the mechanical properties of SFPs and the results are compared with the experimental findings. The results show that the model captures the uniaxial compressive strength and stiffness for all materials examined. The model is further used to evaluate the effect of properties of individual elements of SFP on its stiffness and strength. The feasibility of using the proposed modelling approach to optimize the material design of SFP is discussed., QC 20240412

Aggregate contacts significantly affect the mechanical behavior of asphalt concrete. However, there still lacks an effective way to account for them in numerical modeling. Therefore, to address this concern, a new virtual-specimen-based modeling approach was developed in this study by simplifying aggregate particles in asphalt concrete as spheres and incorporating aggregate contacts through Contact Region (CR) elements. The complex moduli of both gap-graded and dense-graded mixtures were predicted using this approach and compared with those predicted using the conventional image-based modeling approach and laboratory-measured values. The virtual-specimen modeling revealed that the CR in the gap-graded mixture with a higher proportion of large aggregates can better transmit load among aggregates than in the dense-graded mixture. Both modeling approaches were found to provide good prediction accuracy, but the stress distributions in the virtual-specimen models were more uniform and continuous, leading to better computational convergence and the possibility of nonlinear analysis of asphalt concrete., QC 20230904

The stiffness and failure properties of cement-asphalt mastic-aggregate (C-AM-A) interface are among the most important factors affecting the performance of pouring semi-flexible pavement materials (SFP). Therefore, determining the characteristics of C-AM-A interface are essential for guiding the design of SFP from the perspective of interface enhancement. In this study, the failure characteristics of C-AM-A interfaces are examined experimentally and numerically. Firstly, the effects of temperature and the proportion of cement substituting limestone filler on the bonding strength of C-AM-A interface are analyzed via pull-off tests. Then, an innovative test method based on a three-point bending test of C-AM-A beam is proposed to investigate the influence of test temperature and asphalt mastic type on the fracture characteristics of the C-AM-A interface. Finally, based on the cohesive surface techniques, numerical modeling of C-AM-A beam under three-point bending was applied to study the effect of cohesive parameters on the interfacial fracture characteristics. The results show that the interface bonding strength decreased significantly with the increase of temperature. Using cement as a filler improves the bonding strength, fracture strength, stiffness and fracture energy of C-AM-A interface as compared to the case when limestone filler is used. As the temperature increases from -10 degrees C to 20 degrees C, the failure mode of the C-AM-A interface first alters from adhesive failure to mixed failure mode, and then to cohesive failure. It suggests that enhancing the adhesion of C-AM-A interface is more advantageous for improving the fracture resistance at low temperatures, while increasing the interface cohesion is more important at relatively high temperatures. The laboratory test methods, the numerical model and methodology developed in this study are useful to study the failure behavior of C-AM-A interface and optimize the performance of SFP from the perspective o, QC 20230922

A new micromechanical model for predicting viscoelastic properties of mastic is proposed and validated with experiments. The developed model is based on the finite element method and allows predicting the viscoelastic properties of mastic by means of the fundamental mechanical and geometrical properties of its constituents. The influence of modelling parameters on the model’s accuracy is evaluated and optimal parameter combinations are identified. It is shown that the proposed model can capture the measured viscoelastic behaviour of mastics for the range of loading, temperature and material parameters examined. Accordingly, it may be a useful tool for optimizing mastics material design meeting the target viscoelastic properties., QC 20200430