Backcalculation procedure for bonded concrete overlays of asphalt pavement

Bonded concrete overlays of asphalt (BCOA), previously known as ultra-thin whitetopping, have become increasingly common in Illinois in the past 15 years. No methods exist for assessing in situ properties under loading for this type of overlay. A procedure to backcalculate layer properties from falling weight deftectometer tests does exist for concrete slabs on grade with influite dimensions, hut this method is not applicable to finite-sized BCOA slabs with multiple layers and interfaces. Based on two-dimensional finite element modeling of BCOA pavements, a back-calculation procedure was derived for a range of expected slab sizes, effective concrete pavement thicknesses, joint loud transfer efficiencies, und foundation layer stiffnesses. The backcalculated effective concrete thickness quantifies the load-currying capacity of the BCOA pavement, variation of the structural capacity as a function of distance along the roadway, and potentially the condition of the concrete-asphalt bond interface and the underlying asphalt concrete layer. Application of the BCOA backcalculation procedure to falling weight deflectometer data collected from several projects in Illinois confirmed the reasonableness of the procedure through observed performance and estimated layer thicknesses from construction.