Effect of temperature and traffic speed on the asphalt moduli for fatigue cracking and pavement structural design considerations

Abstract

Asphalt pavements exhibit strongly temperature-dependent viscoelastic behaviour resulting in response to load varying with both temperature and traffic speed. To design against fatigue cracking for structural pavement design applications the linear-elastic material response is typically assumed to simplify the calculation of the critical strains in the pavement structure layers. To be representative the simplified pavement model needs to be defined in such a way that it accurately reflects the effect of both temperature and traffic speed on the critical strains used to compare with the material’s tolerable strains. Against this background, this paper presents a method to determine an equivalent asphalt modulus (EAM) for the asphalt layer which represents the effect of temperature and loading speed on the critical tensile strains. The EAM is determined from viscoelastic modelling. Two thick asphalt pavement configurations representative of typical French pavement designs are considered. Results show expected trends of the equivalent asphalt modulus increasing with increasing traffic speed and decreasing with increasing temperature. The application of the asphalt material shift factors allowed building pseudo-master curves for the EAM dataset. Finally, the effect of temperature and pavement structure on the relationship between traffic speed and complex modulus frequency is examined. Results support the use of 10 Hz for 70 km/h at intermediate temperatures currently used for pavement designs in France.