Numerical Simulation For The Void Evolution Under Cement Concrete Pavement Slab

Existence of voids under a slab is one of the common structural damage types in the cement concrete pavements. The appearance of voids is very adverse to the stress distribution in the cement concrete pavements, which greatly affects the pavement performance and the fatigue life. Local void under a concrete slab in the service period of pavements is a common phenomenon. The past investigations focused mainly on the experimental evaluations for voids rather than the theoretical discussions by using mechanics theories. Some investigations for the void evolution problem under a concrete slab has been done in this work by application of continuum damage theory. The main conclusions can be summarized as follows:1. The mechanical modeling for a pavement slab is builded up. By taking the two-order form of the general theory of elastic damage problems, a damage constitutive model with three independent parameters is developed. Based on the proposed damage model, the damage mechanics - additional load - finite element method is then developed. A computer program is written by using the Fortran language in which the plane triangular element with three nodes is adopted. The numerical simulation calculation for the void evolution problem under a concrete slab is carried out in this paper.2. Based on the numerically simulating results, the damaging process in the concrete pavement slab is discussed. First, the general damage evolution process of voids under the pavement slab is introduced, and the damage evolution forms of voids under the slab under the different loads are calculated. The void effects under the different loads are analyzed based on the displacement, damage and stress field distributions. Second, the influences of the elastic modulus of the base layer on the void evolution process under the slab are evaluated. The results show that there is no meaning for improving the pavement performance if the base layer modulus exceeds a large value. Third, if there is a void in the base layer under the pavement slab, the existing void would greatly enhance the crack propagation in the slab and greatly reduce the pavement fatigue life. It is seen that the elastic damage theory can correctly describe the damaging process in the cement concrete pavements. It can be taken as a new mechanics approach for the void evolution problem of pavement slabs.3. Fatigue process of an asphalt beam is analyzed and simulated by using the damage mechanics– finite element method, which is also based on the elastic damage theory. A comparison has been made with the experimental results. The validation and accuracy of the proposed damage model used for concrete materials are examined.