Relaxation of Hardening in Asphalt Concrete under Cyclic Compression Loading

The present experimental study investigated the behavior of hot-mix asphalt (HMA) under repetitive creep and recovery loading. Cylindrical samples of HMA were subjected to trapezoidal and haversine loading followed by unloading. Different amounts of unloading (stress reduction) and relaxation periods (rest periods in complete unloading) were tested. The measured vertical deformation was decomposed into viscoelastic and viscoplastic components. It was observed for cyclic loading that an increase in unloading and/or relaxation period increased the recovery of viscoelastic strain, which in turn increased the accumulated viscoplastic strain in subsequent loading cycles. It appears that repetitive creep and recovery loading caused slight reorientation of the aggregates and changes in the microstructure. This led to relaxation of stress hardening of the materials and resulted in higher viscoplastic strain in subsequent cycles. (C) 2016 American Society of Civil Engineers.