Asphalt-related temperature correction of deflections measured in central FWD tests on a concrete-over-asphalt composite pavement

This study focuses on the seasonal variations observed in five Falling Weight Deflectometer (FWD) tests conducted on a well-instrumented composite pavement. The main objective is to investigate the underlying mechanisms driving these seasonal variations and propose a method to facilitate the comparison of the different FWD tests. The stiffnesses of concrete, asphalt, and cement-stabilised layers are characterised individually. The stiffness of the subgrade is back-calculated using multi-layered simulations. These simulations also enable computation of deflections for different asphalt temperatures. The results allow for developing a method which converts measured deflections into corrected deflections referring to an asphalt reference temperature. Remaining seasonal variations of the corrected deflections refer to the subgrade. Corresponding k-values of the AREA4 method correlate well with seasonal variations of the stiffness of the subgrade. Finally, an alternative temperature-correction approach, requiring measured deflections only, is developed. Corrected deflections allow for quantifying seasonal stiffness variations of the subgrade.