Study on the evolution pattern of in-service modulus for semi-rigid base layer based on curing-state correction

Laboratory tests show that prolonged curing enhances specimen modulus. However, when evaluating in-service modulus of base layers in asphalt pavements, most studies emphasize traffic loading while neglecting time effect. To address this gap, this paper develops an evolution model of the in-service modulus for semi-rigid base layers considering coupled effects of traffic loading and time. First, Falling Weight Deflectometer testing was conducted to back-calculate moduli under varying loading levels and service ages. Then, assuming time-dependent effects remained consistent within each six-month interval, regression analysis was performed separately for each period to derive modulus evolution trend. From this, the unloaded modulus at different ages was obtained to quantify time factor (Kt ). Based on Kt ​, moduli measured at different ages were normalized to a reference age, and regression fitting was subsequently performed to characterize deterioration trend under repeated loading, expressed by loading factor (KN ). Results indicate that the time-dependent effect follows a characteristic increase-decrease-stabilization pattern, well described by Gamma-type function. The peak unloaded modulus within the first year can reach approximately 1.3 times the initial value. By contrast, traffic loading induces continued damage described by structural behavior equation. The findings improve prediction of base layer’s modulus and support pavement management decision-making.