Study On Mechanical Simulation And Crack Propagation Law Of Rubber Powder And Cement Stabilized Waste Semi-rigid Base Materials

China produces a large amount of waste semi-rigid base material and waste rubber powder every year,reuse both in road base construction,not only can solve the problem of solid waste pile,but also can realize the green sustainable development of resources.The waste semi-rigid base material as recycled aggregate preparation of new cement stabilized macadam mixture will affect the mechanical properties and crack resistance of the mixture,using the elasticity of rubber powder,by adding rubber powder can improve the shrinkage resistance of the mixture,and effectively prevent and control the reflection cracks of asphalt pavement.However,if recycled aggregate and rubber powder are added into the cement stabilized macadam mixture,the mixture will form a complex structure of multi-phase materials,so it is especially important to investigate the mechanism of the influence of recycled aggregate and rubber powder on the performance and the crack expansion law of the mixture.Firstly,based on the anti-cracking gradation,six kinds of rubber powder and cement stabilized waste semi-rigid base materials containing different amounts of recycled aggregate(0%,30% and 100%)and different kinds of rubber powder(modified rubber powder and nonmodified rubber powder)were designed and their mechanical properties,frost resistance and anti-cracking properties were measured.It was found that the mechanical properties,cracking resistance and frost resistance of the mixtures decreased with the increase of recycled aggregates at the ages of 7d/28d/90 d.At the same time,the mechanical strength,crack resistance and frost resistance of the mixtures in the modified rubber powder group were significantly improved compared with the mixtures in the unmodified rubber powder group under the same aggregate conditions at 7d/28d/90 d ages.Secondly,according to the structures of new aggregate,recycled aggregate,rubber powder and cement mortar existing in the 3D discrete element model of the mixture,the linear contact model and parallel bonding model were chosen to characterize the mutual contact between each structure respectively.The step-by-step calibration method was used to calibrate the fine view parameters of the mixture,and the results were verified and calibrated with the indoor test results,finding that the deviation of different types of mixture simulations from the indoor test results was less than 10%,which verified the feasibility of using the 3D discrete element method in the mechanical simulation of rubber powder and cement stabilized waste semi-rigid base materials.Thirdly,based on the 3D discrete element model,the damage displacement,contact cloud and mechanical transfer path changes of each structure in different types of mixtures were investigated in three stress modes(compression,compression-tension and bending-tension states).It was found that with the increase of recycled aggregate admixture,the mixture structure is prone to form large structural damage in the compressed state,resulting in the loss of the mixture skeleton and the reduction of the integrity,which eventually leads to the decrease of the load-bearing capacity of the mixture.Rubber powder forms a good stress transfer chain with coarse aggregate and cement mortar in the mixture system,and shows the role of dispersing stress with high elasticity in the system.Finally,the influence of different recycled aggregate admixture and different types of rubber powder on the crack expansion law of the mixture under three stress modes was explored,the process of structural damage formation was analyzed,and the damage mechanism of the mixture was explored from the fine viewpoint.It was found that the mixture under anti-cracking grade reflected strong rigidity,and after adding modified/unmodified rubber powder,the flexibility of the specimens increased,so that the crack expansion law of the mixture was changed,and the damage form of the mixture was changed to some extent,so that the mixture was converted from brittle damage to plastic damage.The mixture mixed with recycled aggregates produced large cracks under different stress patterns,and the large cracks penetrated each other to form penetration cracks under load,which led to the decrease of the mechanical properties of the mixture.In summary,in this paper,by adding modified/unmodified rubber powder to cementstabilized waste semi-rigid base materials,the cracking and frost resistance of the mixtures can be improved while ensuring their mechanical strength.The effects of different recycled aggregate admixtures and different types of rubber powder on the performance and crack expansion patterns of rubber powder and cement stabilized waste semi-rigid base materials were investigated through 3D discrete element simulation tests to promote the use of waste semi-rigid base materials and rubber powder in the field of road engineering construction.