Relating Unbound Pavement Layers’ Moduli—Laboratory vs. Field Tests

The laboratory-determined resilient moduli (M_R) of various unbound pavement layers, obtained from multiple sections of six different projects, were compared with moduli determined using in situ field tests, including falling weight deflectometer (FWD), lightweight deflectometer (LWD), and direct cone penetrometer (DCP). While the FWD deflections were measured over the finished pavement surfaces, the LWD and DCP tests were conducted on the surface of the compacted unbound layers. The laboratory subgrade M_R values were comparable to the median FWD- and DCP-determined moduli. Similarly, the subbase and base layer M_R values were in close agreement with the FWD backcalculated moduli. Plots are presented to estimate potential correlations between the lab- and field test-based layer moduli. When the exact sampling locations were unavailable for these correlations, the median moduli estimated from the different field tests were compared to their laboratory values. Correction factors were obtained without accurate field vs. laboratory correlation to estimate different layer moduli from the field-testing data. The comparison showed that among the three field tests evaluated, the FWD backcalculation moduli results with negligible bias and standard error compared to their lab-determined values, especially for the base layers that require little to no correction. This finding suggests FWD testing over the finished pavement surface reasonably estimates the unbound layer moduli for use in design. The LWD and DCP testing may quantify individual layers’ density to identify the relatively weaker areas during construction.