Comparison Study on Various Backcalculation Techniques for Estimating the Resilient Modulus of Asphalt Pavement Layers

Pavement stiffness indicators such as elastic/resilient modulus (MR) can be determined by either destructive (core sampling) or non-destructive testing (FWD). This study uses a Falling Weight Deflectometer (FWD) to determine MR by analyzing pavement defection. Since MR serves as a significant input parameter for designing pavement crust thickness, inaccurate arrival of MR can significantly impact overlay designs. Although several back-calculation programmes are available, large variability is observed in the outputs obtained due to seed moduli and other input parameters. Also, based on the algorithm used in the software, the back-calculated MR values will deviate from the laboratory-measured values. In this paper, FWD investigations were performed and analyzed for Indian highways. The reliability of five different back-calculation computer programs (i.e., KGPBACK, MICKBACK, BAKFAA, MODULUS, and ELMOD) was assessed and compared. The major objective is to find the computer program that predicts the reliable MR values of asphalt pavement layers. Core samples were taken from the field and tested for resilient modulus. The study results show that the BAKFAA and ELMOD computer programs provide more reliable moduli than the other software.