ENVIRONMENTAL INFLUENCES ON WARPING AND CURLING OF PCC PAVEMENT
This research was conducted to analyze the influence of moisture content in concrete pavement slabs on warping and curling of Portland Cement Concrete (PCC) pavement. To do this, temperature and deflection data measured in an instrumented test runway pavement at the Denver International Airport [1-3] was used. Variation in temperature gradient over the slab thickness was computed and plotted against time, for both the summer and the winter. Deflections of the PCC slabs and the base layer were compared to identify gaps between the two layers caused by slab warping and curling. It has been found that such gaps physically exist and that the magnitude of the gaps varies with time as temperature gradient does. The gap magnitude at various locations within the slabs, together with the temperature gradient, was plotted on the same time scale. This has made it possible to quantify the influence of moisture gradient in the equivalency of temperature gradient on slab warping. As expected, the equivalent temperature gradient of moisture content also varies with time and is dependent on the day of the year and the hour of the day. Based on the available data, this value varies in the neighborhood of 0.10 to 0.27 (oC/cm), which is about half of the maximum positive temperature gradient (when the bottom of the slab has a lower temperature than the top of the slab) in the summer and close to the maximum positive temperature gradient in the winter. The analysis has also proved the fact that the existence of moisture gradient strengt hens the effect of negative temperature gradient (when the bottom of the slab has a higher temperature than the top of the slab), but weakens the effect of positive temperature gradient.