Abstract
A methodology for evaluating the condition of jointed portland cement concrete pavements (JCP) by non-destructive deflection testing was recently applied on the N4 (National Route 4) between Middelburg and Witbank in South Africa. A set of two calibrated Multi-Depth Deflectometers (MDD) measured traffic-associated vertical absolute deflections at both sides of a transverse joint. An 80 kN rear axle truck was used to simulate traffic. A piezo-electric film strip triggered the data accumulation process. Joint efficiencies were then calculated from absolute deflections measured by both MDDs. It was found that temperatures at the top and at the bottom of the slab, as well as temperature gradient, have a significant effect on maximum absolute deflections and hence joint load transfer efficiencies. For the range of vehicle speeds considered in this study, the effect of speed on deflections and joint efficiencies was found to be insignificant if compared with the temperature effect. Deflections decreased for increasing surface temperatures while joint load transfer efficiencies calculated by means of the AASHTO formula did not follow a definite trend owing to the influence of the temperature gradient, the surface temperature and the front axle of the test vehicle. Joint load transfer efficiency is one of the inputs of theoretical-mechanistic models for the calculation of stresses and deflections in the pavement structure. In this paper, charts have been developed for deflection vs joint efficiency and stresses vs joint efficiency. Stresses and deflections have been calculated by the ILLI-SLAB finite element computer program code. Calculated stresses and deflections increased significantly for decreasing joint efficiencies. There was a discrepancy between theoretically calculated results and deflections measured in the field. The effect of temperature, the curvature of the slab, the load configuration and the dynamic application of loads were not considered in the parametric study. This is seen to be the major cause of this discrepancy.
Published Version
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