Falling weight deflectometer testing (FWD) is a non-destructive testing method for pavements, which involves measuring the response of a pavement to a a falling weight. For jointed plain concrete pavements (JPCP), the response of the pavement to the FWD load can be used to backcalculate the pavement layer properties, estimate the performance of the joints, and detect voids. Temperature and moisture gradients in the concrete layer of JPCPs induce curvature in the slab, altering the support conditions of the slab throughout the day. This change in support condition can have a significant effect on FWD testing results.
A combination of computational analyses, interpretation of field trials, and statistical analysis was used to evaluate the effect of slab curvature when interpreting FWD data. It was determined that backcalculation of the modulus of subgrade reaction (k-value), is sensitive to slab curvature, if the equivalent linear temperature gradient (ELTG) in the slab is less than 0.5 °F/in especially. for pavements with stiff supporting layers. A backcalculation procedure was developed to backcalculate the modulus of subgrade reaction using FWD testing when positive temperature gradients are present. The measured load transfer efficiency (LTE) for doweled JPCP slabs was found to be at a minimum when the slab is approximately flat and increase as a positive or negative temperature gradient develops. The measured differential deflection for doweled slabs was found to be at a maximum when the slab is approximately flat or with a negative temperature gradient, depending on the condition of the dowels. A void detection model for doweled JPCP pavements was developed using LASSO logistic regression, which outperforms currently available void detection techniques. Finally, a temperature prediction model was developed, which predicts the pavement temperature profile as a function of the weather conditions. The developed models are all packaged in the University of Pittsburgh FWD Analysis of Concretes Slabs (PITT-FACS) web tool, so that they can easily be used by practitioners
