Non-linear modeling of the influence of rest period on healing behavior of asphalt concrete mixtures

Realistic traffic conditions involve random load amplitude, frequency (speed) and rest periods between load applications. Out of these three factors, one factor which can be controlled and which can throw light on the viscoelastic response of the asphalt concrete mixtures and to some extent on the “healing” nature of these materials is rest period between loadings. An experimental investigation was designed to study the behavior of asphalt concrete mixture during the rest period of a creep and recovery test by providing a prolonged rest period between each set of 100 test cycles. The test was carried out in the unconfined and confined condition, at temperatures of 20, 40 and 55°C. During rest periods, the confinement pressure was maintained in the material. It was observed that during the rest period, the material attained a beneficial internal structural state that required a lesser time to reach a ‘stable’ state when loaded afterwards. It was noted that confinement pressure was necessary for assisting the healing of the material. To model this response of the material, a non-linear upper convected Burgers’ model was used. The model parameters could explain the material behavior and the conditions under which any beneficial internal structural changes happen in the material.