Comparison of Unbound Material Moduli — Laboratory vs. Field tests

The unbound material characterization can be based on laboratory or in-situ field tests. Laboratory results may not consider the stress state of the material in the field, while in situ testing is non-destructive and can be more efficient. However, there could be differences in the results based on lab vs. field material properties. This paper presents the laboratory resilient moduli (MR) results of various unbound pavement layers obtained from multiple sections. It compares them with field MR values obtained using falling weight deflectometer (FWD), light weight deflectometer (LWD), and direct cone penetrometer (DCP). The measured surface FWD deflections were used to backcalculate the MR values of different layers, while the LWD and DCP tests were conducted on the surface of the finished unbound layers to estimate their moduli.

The results show that lab subgrade MR values were comparable to the median FWD and DCP moduli values. Similarly, the lab subbase and base layer MR values were in close agreement with the FWD moduli. Without suitable field vs. laboratory correlation between the different layer moduli, the paper includes correction factors for the field-testing data. The comparison showed that among the field tests, the corrected FWD results show negligible bias and standard error compared to lab values for subgrade, subbase, and base layers. This finding suggests that FWD testing over the finished pavement surface reasonably estimates the unbound layer moduli for use in design. The LWD and DCP testing can be used to quantify individual layers' stiffness to identify the relatively weaker areas during construction.