Relationship among cohesion, adhesion, and bond strength: From multi-scale investigation of asphalt-based composites subjected to laboratory-simulated aging

Abstract

Identifying the properties of the bond strength between aggregates and asphalt binders is critical to understand the strength and fracture behavior of asphalt mixture. Some efforts have been made on the effect of aging on the bonding property of the asphalt binder. However, there is no consensus result and the mechanism that drives the change of bonding property remains unclear. The objective of this study is to investigate the influence of aging on the bonding property, and to explain the reason lies behind. To achieve this goal, four neat asphalt binders were treated with short-term aging and long-term aging. The bond strength and the adhesion force were measured by binder bond strength test on a macro scale and atomic force microscope on a micro scale, respectively. Based on the result obtained in this study and previous publications along with the adhesion theories, it is found that a moderate aging contributes to the bond strength while a sever aging does not necessarily improve the bond strength. The change of bond strength under an aging condition can be explained by the cohesion force in asphalt binders and the adhesion force between asphalt binders and aggregates. Based on the results, it can be concluded that the cohesion force increases with aging time as a result of asphaltenes association. The adhesion force increases initially and then decreases, and the wettability is thought to be responsible for the reduction of adhesion force. The adhesion reduction can be observed on the three phases (catana phase, peri phase, para phase) of the asphalt binders, which leads to the adhesion reduction on the whole asphalt binders. These findings help to provide a better understanding of the change of bonding property of asphalt binders during an aging process, which contributes to the improvement of bond strength by enhancing the wettability of each phase in asphalt binders appropriately. The results have practical significance and can help to optimize the materials production process.