Influence of the thermal expansion of bitumen on asphalt self-healing

Abstract

The self-healing of cracks in asphalt mixture is mainly due to the drain of the bitumen contained in the space between the aggregates, into the cracks. Until now, it was believed that the physical principles affecting the flow of bitumen are influenced by gravity and surface energy of bitumen and the aggregates. In this study, we show that the thermal expansion of bitumen plays an important role in the self-healing of asphalt mixture. To demonstrate this, asphalt mortar beams were manufactured and broken in two pieces by means of three-point bending tests. Self-healing was induced in asphalt mixture by increasing its temperature using a convection oven, at temperatures that ranged from 40 °C to 120 °C. The self-healing ratio was calculated by comparing the force required to break the test specimens before and after heating.Furthermore, a test was designed that consisted of bitumen raising through a capillary tube from a bitumen container. To account for the effect of thermal expansion, the bitumen container was fully enclosed except for the capillary tube. To account for the effect of surface energy on the bitumen’s capillary flow, the capillary tube was placed in a container that was open to the atmosphere. The rise of bitumen was monitored at temperatures that ranged from 40 °C to 120 °C. Finally, activation energies were derived from the rise of bitumen in the capillaries, viscosity changes and the self-healing progression. It was found that the activation energy of asphalt self-healing is similar to that of bitumen rising due to thermal expansion, which confirms the contribution of thermal expansion on asphalt self-healing by the effect of increasing temperature.