Stress-Dependent Behavior of Lightly Stabilized Industrial Waste Subbase Using Falling Weight Deflectometer

Pavement layers exhibit stress-dependent behavior, characterized by using a laboratory resilient modulus (M_r) test. However, the field behavior of such materials seldom matches with the laboratory because of changes in the state of stress, material matrix, and loading patterns. In this study, the nonlinear behaviors of three innovative fly ash-based lightly stabilized industrial waste mixes that are proposed to replace the granular subbase of flexible pavement are characterized and compared in the laboratory and field for the first time. Nine full-scale pavement test sections were constructed with three varying thicknesses of waste mix subbase layers, namely, fly ash +  5 % lime (FAL), 70 % copper slag +  30 % fly ash (CFA) and 80 % fly ash +  20 % granulated blast furnace slag (FAG). Repeated load triaxial tests on lab samples and multiload falling weight deflectometer (FWD) tests (40 kN, 55 kN and 70 kN) on test sections conducted for three years post-construction were used to extract the nonlinear behavior of M_r and the FWD backcalculated modulus (E_FWD) of subbase layers. Effects of curing and traffic damage on the nonlinear parameters of E_FWD were investigated. Stress-dependent conversion factors based on two different constitutive models were established to convert M_r to E_FWD at different points of the subbase service life. Stabilized waste mixes exhibited stress hardening with increasing bulk and deviatoric stresses both in the field and laboratory. Curing increased E_FWD and reduced the effect of stresses on the E_FWD. In contrast, traffic damage imparted the opposite effect, as the stabilized waste mixes transformed into a cracked and blocky mass. The results of this study will allow practitioners to predict the field performance of waste mix subbase with great accuracy, resulting in a reliable design and possible cost savings.