Interpreting falling weight deflectometer results for curled and warped Portland cement concrete pavements

Falling Weight Deflectometer (FWD) test results of concrete pavements are influenced by the presence of temperature and moisture gradients in the pavement. When the pavement surface is warmer and/or has a higher moisture content than the bottom of the pavement, the slab corners tend to curl or warp downward, exaggerating the level of support present at the corners and sometimes leaving the center of the slab unsupported. If the pavement surface is cooler and/or drier than the bottom of the pavement, the corners of the slab tend to curl or warp upward, resulting in a loss of support at the corners and edges of the pavement. Performing FWD testing at times when pavement support varies due to the presence of temperature and/or moisture gradients results in the measurement of nonrepresentative deflections and can lead to inaccurate evaluations of material properties and pavement conditions. A study was performed to quantify the effects of curling and warping on FWD-based evaluations of concrete pavements and to develop techniques for compensating for the effects of temperature and moisture gradients in the analysis of FWD data.; Deflection, strain, temperature, moisture and surface profile data were collected from the concrete pavement test sections at the Minnesota Road Research Facility (Mn/ROAD). Data were collected throughout 24-hour periods at different times of the year so conditions representing various thermal and moisture gradients could be included in the study. The measured slab responses were compared to analytical results generated using the pavement finite element analysis program ISLAB2000. The field data were used to generate models for predicting slab curvature, slab movement at the corners and a correction parameter used for interpreting FWD data when identify voids under the slab.