Integrating FWD test and laboratory observation for assessing the damage state of semi-rigid base in asphalt pavement

Base layer’s condition assessment provides essential references for pavement maintenance and rehabilitation. However, as base layer is within the pavement structure, direct observation of its condition is difficult, which limits the validation of evaluation indicators against actual damage conditions. This paper aims to propose a non-destructive testing (NDT) framework for assessing the damage states of semi-rigid base, with its reliability validated by laboratory observation. First, Falling Weight Deflectometer (FWD) testing, traffic measurement and core sampling were conducted on two in-service pavements. Then, base layer’s moduli under different magnitudes of axle loadings were back-calculated via FWD deflections, and used to predict base layer’s initial modulus (i.e., E₀), whose prediction accuracy was verified by comparing it with the results of uniaxial compression test on core samples. Based on the back-calculated moduli and initial modulus, the damage state of base layer was assessed, and the assessment accuracy of this new FWD-backcalculation-based method was validated by laboratory observation on actual damage states of core samples. Finally, the proposed method was in comparison with conventional assessment methods to prove its advancement. The results indicate that the fitting error of predicted $E_0$ is below 0.5 % and the damage states assessed by the proposed method align closely with the observed damage states. Besides, comparisons between the proposed and conventional methods illustrate the former one is advanced in identifying different damage states. The findings of this research are expected to offer insights to assist in detecting damage states of semi-rigid base and making maintenance strategies for asphalt pavement.