Equivalent AC layer thickness conversion and deflection index correction based on structural negative thixotropic effect

To reveal the essential law of asphalt pavement structure deflection under instantaneous loads of falling weight deflectometer (FWD), five structures on the RIOHTrack full-scale test track under the same subgrade and base conditions were seen as benchmark structures, and the variation law of asphalt pavement deflection index with thickness under instantaneous impact loads of FWD was analyzed. Based on the principle of equal stiffness, the equivalent asphalt concrete (AC) layer thickness for different base structures of RIOHTrack was derived, and the 19 pavement structures were simplified into a double-layer system consisting of equivalent AC layer + subgrade. A simple design method for asphalt pavement structure based on bearing capacity index was proposed, and a comprehensive correction model for theoretical deflection index was constructed by considering soil modulus and equivalent AC layer modulus of the superstructure. Research results indicate that under instantaneous loads of FWD, asphalt pavement structures have significant negative thixotropic effects. The deflection index shows a decreasing trend with the increase in asphalt layer thickness under the same subgrade and base conditions. This phenomenon has been verified under different load levels and environmental conditions. The correlation between the equivalent AC layer thickness of the pavement structure and the measured deflection basin area is over 99%, which proves that the proposed equivalent AC layer thickness conversion method has good reliability. Compared with the traditional comprehensive deflection correction models, the F correction model proposed considers both the subgrade and the superstructure modulus, thus compensating for the deficiency of existing deflection correction methods that fail to consider the impact of the pavement structure form. The research results can provide a simple and feasible method for the asphalt pavement structure design.