Validation of the dynamic response of the HMA layer in an inverted pavement measured by strain foils

Abstract Strain in pavement caused by traffic loading is a critical driver for various distress mechanisms. In this study, strain foils (SFs) are utilized to measure longitudinal strains at the bottom of a hot mixed asphalt (HMA) layer in an indoor inverted pavement. The validity and reliability of SF-measured strain are investigated through three tests using a heavy vehicle simulator (HVS). The three tests focus on the consistency and stability of strain measured by individual SFs and various SFs installed at similar positions, as well as the consistency of strain measured by SF and an asphalt strain gauge (ASG) at different test speeds, load levels, and loading cycles in an accelerated pavement test (APT). Fast Fourier transform is utilized to filter out interference in the raw SF strain data. Filtered SF-measured strains were converted into ASG-measured strain based on effective gauge lengths. Research results show that converted SF-measured strains did not reveal a significant statistical difference compared with strains simultaneously collected by ASG under different test loads and speeds throughout the APT at 300,000 repetitions. Moreover, individual SF can provide consistent results with the coefficient of variation (CV) less than 3.3 % under different speeds and load levels, and SFs installed at similar positions showed similar average maximum strain variations (MSVs) with a maximum difference of 5.8 %. Moreover, the linear correlations between the average MSV and the test load, as well as the speed further verified the validity of SF-measured strain. It is believed that SF could be a viable alternative for strain monitoring in asphalt pavement.