y$D51101A The present design curves for concrete pavements in Road Note 29 are largely based on observations made on experimental roads prior to 1970, when none had carried more than 10 million standard axles. By 1985 these and other experimental sites had carried considerably more traffic and provided broader data on which to base future designs. The performance of 29 unreinforced and 42 reinforced forms of construction were analysed to establish new design curves. The structural performance was assessed and pavement life equations were derived by multiple regression analysis. Tensile stresses generated, by traffic and temperature, at the underside of the slab, were calculated for a number of different pavement configurations using a multi-layer linear elastic model. The ratio of strengths of the unreinforced concrete to the calculated stresses in these pavements was found to be directly related to pavement life determined from the regression equation. The existence of this unique relationship suggests a possible design criterion and supports the realism of the regression equation by indicating a credible mechanism of pavement deterioration. Good agreement was found between slab designs derived from the regression models and those obtained by the AASHTO design method; this enabled the enhanced performance expected from pavements with tied shoulders to be evaluated. (A)

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