Dynamic Back-calculation for Evaluating Structural Degradation of Transverse Joint in Concrete Pavement

In this study, test sections of a concrete pavement were constructed on a circular accelerated pavement testing (APT) roadway and subjected to 5.2 million of 49kN equivalent single wheel loads (ESWL). The test pavement has four sections with presence and absence of steel mesh in concrete slabs and hot asphalt mixture interlayer (HMA-IL) beneath the slabs, and the effects of these devices on joint degradation were investigated. Also, transverse cracks were induced at the mid slab to examine performance of pavement slabs after fatigue transverse cracks occur. During the loading test, FWD tests were regularly performed and structural changes were evaluated with FWD dynamic back-calculation.Joint degradation process was divided into fourteen stages from structurally sound states to severely degraded states with broken dowel bars and a gap underneath the joint. These degradation states were modeled with Dynamic 3DFEM that takes into consideration dynamic nature of FWD impact loading. The back-calculation identifies not only layer moduli but also the degradation stage at a doweled joint of the concrete pavement. The results of the analysis revealed that the amount of steel mesh was insufficient to keep the crack opening tight. After dowel bars did not work, a gap formed and expanded under the slabs but HMA-IL prevented further expansion of the gap. In spite of those severe degrading conditions, the stress at the slab bottom did not significantly increase and the slabs have kept sound for more than 5 million of ESWLs, which is much longer life span than we expected. Excavation survey on the test section, however, revealed that gap between the slab and base course surface were found, which corresponds to the stage identified with FWD back-calculation.