Comparison of PCC Elastic Modulus for Rigid Pavements – Laboratory versus Field

Deflections measured using Falling Weight Deflectometer (FWD) device are used to backcalculate the elastic modulus (Epcc) of the concrete slab of a jointed Plain Concrete Pavement (PCP). The two procedures used to estimate the Epcc of the PCP slab from the deflection basins include the AREA method and the Best-Fit method; the latter is used by the Long-Term Pavement Performance Program (LTPP) in the US and Canada. Generally, the Epcc derived from any of the backcalculation processes is higher than the laboratory-based values. Therefore, this study compared the laboratory-based Epcc values with the FWD-based values for the LTPP Specific Pavement Section-2 (SPS-2) sections. The comparison used moduli values from the LTPP SPS-2 database with the same test year and month for both the laboratory and FWD tests to ensure that the pavement has the same age. To reduce the sum of squared errors between the laboratory- and FWD-based moduli, an estimated reduction factor of 63 % for the FWD-based values is suggested based on the data analyzed in this study. The reduction factor caters to the overestimated Epcc values caused by static and dynamic loading conditions in the laboratory vs. field during the FWD tests and material vs. pavement system (i.e., laboratory tests only the concrete behavior while FWD tests the entire pavement structure).