The erosion analysis used in the development of the PCA pavement design method takes account of the fact that erosion failure modes are more closely related to pavement deflections than to pavement stresses. This has an equivalent fatigue damage value of typical heavy vehicle wheel placements.
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An analysis of typical heavy vehicle wheel load locations was undertaken to arrive at a design value of around 6% of heavy traffic occurring at the slab edge. The PCA pavement design method accounts for the different stresses produced by loading at different distances from the edge. This means that the combined warping and curling effects will have a negative net impact on the stresses produced on the slab during loading. This can be justified for the fatigue case as the temperature and moisture content of the slab will generally be higher at the bottom of the slab than at the top. This moves the edge loading condition to an interior loading condition, significantly lowering the maximum stresses produced.Īgain the PCA pavement design method omits the effects of warping and curling on the slab. The edge loading condition can be reduced significantly by including a concrete shoulder.
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This is far enough away from the slab joints for them to have a significant impact on the stresses developed in the pavement. The fatigue analysis used in the PCA pavement design method is based on the edge stress condition where the load is situated on the edge of the mid-slab. One criticism of the Westergaard method is that is does not take account of erosion type failures which were found to be very common during the AASHTO Road Test for concrete roads. Erosion failure occurs when pumping or erosion of the pavement foundations leads to failure of the pavement and joint faulting. Fatigue failure occurs when concrete pavements fail due to the repeated damage caused by many millions of loading cycles. The PCA procedure includes two main modes of pavement failure, fatigue or erosion. The finite element model was populated largely by Pickett’s equations based on Westergaard’s initial stress and deflection analysis. The PCA method was developed based on finite element calculations of pavement stresses and deflections which were then calibrated with some simple design and performance criteria to create a series of design tables and charts. Unlike the AASHTO rigid pavement design method which is empirically based on road test data, the PCA method was an early attempt at a mechanistic design method. It included the erosion design condition and tables were included for the design of pavements with concrete shoulders and with undoweled joints. This method was improved in 1984 to include a wider range of design considerations and pavement types. The Portland Cement Association (PCA) developed a new rigid pavement design method published in 1966.