Effect of slab curling on backcalculated material properties of jointed concrete pavements

Different backcalculation algorithms produce different elastic moduli which are used as a key indicator of structural capacity of concrete pavements. Accordingly, the elastic moduli backcalculated by various backcalculation algorithms have been evaluated using the elastic moduli of cores of concrete pavement layers measured in the laboratory. However, variation in the backcalculated elastic modulus, even within a pavement section, is a significant issue in the concrete pavement evaluation. In the present work, deflections of jointed concrete pavement under a Falling Weight Deflectometer (FWD) loading were measured for 48 h at the KEC (Korea Expressway Corporation) test road. The curling effect on the backcalculated elastic modulus of the concrete slab was investigated using the different temperature gradients and slab curl conditions arising at different measurement times. The elastic moduli of the concrete pavement layers were backcalculated using the measured deflection basins, the AREA method and the method of equivalent thickness (MET). A basic concept to adjust the cyclic variation in the backcalculated elastic modulus due to the slab curling using the temperature difference between the top and bottom of the slab is presented. Measured data of deflection and load transfer efficiency (LTE) of the tested joints verify the curling effect on the backcalculated structural capacity of the concrete pavements.