Impact of temperature and moisture on the tensile strain of asphalt concrete layers

Moisture in unbound layers and temperature in asphalt layers affect the structural response of pavements, such as the tensile strain at the bottom of asphalt concrete layers. Previous studies have proposed relationships for estimating tensile strain at the bottom of an asphalt layer from Falling Weight Deflectometer (FWD) surface deflection measurements. These relationships have been developed based on theoretical calculations of strains and surface deflections. The main objective of this study was to evaluate these relationships using measured FWD deflections and tensile strains at the bottom of asphalt concrete layers. Three instrumented test structures were considered in the study. FWD and strain measurements were conducted at varying groundwater levels in the subgrade and temperatures in the asphalt concrete layers. The results revealed that the relationships have poor agreement with measured strains. A new relationship is proposed that incorporates the volumetric water content in the subgrade and the temperature in the asphalt layers in addition to the surface FWD deflections.