Using the light weight deflectometer with radial offst sensors on two-layer systems for construction quality control/quality assurance of reclaimed and stabilized materials

Abstract

The light weight deflectometer (LWD) is a portable device used to perform a dynamic plate load test developed to rapidly assess the in situ elastic modulus of surface soils. LWDs are particularly suited for the evaluation of compacted base and subgrade layers prior to application of the pavement surface or wearing course and have slowly gained acceptance for purposes of quality control/quality assurance (QC/QA) and nondestructive evaluation in earthwork construction. The use of LWD testing has been prompted by the need for performance related specifications of pavement construction. In this sense, techniques are needed to measure the designed-for properties of pavement layers, e.g., resilient modulus. The shift towards performance-based specifications requires this, and is critical for mechanistic empirical pavement design. The relatively recent inclusion of radial offset sensors with LWD testing has stemmed from the well-established Falling Weight Deflectometer (FWD) testing method of backcalculating individual layer moduli from a measured deflection bowl. However, very little research exists in the literature exploring the applicability of backcalculating layer moduli from LWD tests with radial offset deflection sensors, particularly in the field on active construction sites. Furthermore, LWD use on stabilized or lightly bound layers as well as the use of radial offset deflection measurements to isolate individual moduli has not been heavily addressed in the literature. To this end, a thorough investigation of the applicability of LWD testing on stabilized layers using radial offset deflection measurements is needed to determine if using the LWD is feasible for construction QC/QA of stabilized base layers on low volume roads. LWD testing data with radial offset deflection measurements on stabilized base layers from seven field sites were rigorously analyzed to determine if radial offset sensors are a necessity for QC/QA. Several backcalculation methods, both static and dynamic, were explored to isolate individual layer moduli and characterize the curing behavior of the stabilized layer. It was found that radial offset deflection measurements are critical to the assessment of both the stabilized base and subgrade layers and should be incorporated into LWD testing for QC/QA. Backcalculation results demonstrated the dynamic nature of the LWD test to be significant and, consequently, quasi-static analysis of measured deflections may lead to inaccurate moduli estimates.