Three-dimensional finite element analysis to evaluate reflective cracking potential in asphalt concrete overlays

Many existing pavements, both rigid and flexible, have been rehabilitated with bituminous overlays. However, reflection cracking occurs in these new overlays due to the movement of existing pavements under environmental or traffic loads, and/or a combination of both. To solve the reflective cracking problem, the localized responses in the overlay close to the joints/cracks need to be understood first before more detailed studies can be conducted in future.; An airport rehabilitation demonstration project has been established at the Rantoul National Aviation Center (NAC), which was already instrumented with in-place pavement sensors. It has existing Portland cement concrete pavements which were overlaid with asphalt concrete in fall 1999. Several different rehabilitation methods at Rantoul NAC were designed to mitigate reflective cracking. Even though many methods have been used for mitigating reflective cracking, none of the methods have been investigated with sophisticated models with nonlinear material modeling. Therefore, pavement sections from the Rantoul NAC demonstration project were modeled with 3-D finite element analysis using a contact algorithm between PCC slabs and the underlying layer, and viscoelastic material modeling of layers containing asphalt binder. The critical responses in asphalt overlays in the vicinity of the joints, as well as the benefit of using a crack arresting interlayer, were evaluated in this study. Measured deflections during FWD testing were used to calibrate the models and estimate the subgrade modulus with dynamic finite element analysis. Realistic pavement temperatures throughout the pavement thickness were predicted with the Integrated Climatic Model (ICM), and calibrated with field pavement temperature measurements from Rantoul NAC airport.; The study revealed that the crack treatment interlayer, ISAC, greatly reduces the tensile stresses at the bottom of the overlay after both the cooling cycle and cooling cycle plus traffic loading. On the other hand, the modified asphalt (PG 64-28) greatly reduces the tensile stresses at the top of the overlay compared to regular asphalt (PG 58-22) at the end of the cooling cycle before traffic loading. It appears that a ductile crack control system (such as ISAC) in cold temperatures can isolate the overlay from underlying existing pavement movements (contraction and curling).