Interfacial Bonding Strength between Cement Asphalt Mortar and Concrete in Slab Track

Abstract

In China Railway Track System II, the bonding of a cement asphalt mortar (CA mortar) layer to concrete slabs is a decisive factor for its durability and serviceability. In this study, the interfacial bonding strength between two types of CA mortar, A/C=0.2 and A/C=0.6 (A/C, asphalt to cement ratio in mass) and the concrete slab was investigated by pull-off tests, and effects of polymer latex, expansive agent, and temperature cycles were considered. Results indicate that the bonding strength of the CA mortar at a high A/C is obviously higher than that at a low A/C. The modification by polymer latex effectively increases the bonding strength and the effect is greater at a higher A/C. Similarly, the presence of expansive agent in the CA mortar increases the bonding strength but the effect is greater at A/C of 0.2 because of a different mechanism. From the microstructural point of view, the bonding strength of the CA mortar at a lower A/C is primarily decided by the mechanical interlocking whereas the bonding strength of the CA mortar at a higher A/C is firmly related to the adhesion of asphalt binder. Temperature cycles decrease the interfacial bonding possibly due to the weakened mechanical interlocking forces at the interface caused by the mismatch deformation between the CA mortar and the concrete slab. The incorporation of polymer latex reduces the temperature sensitivity of the bonding strength at A/C of 0.6. In contrast, the inclusion of expansive agent increases the temperature sensitivity.