Experimental evaluation of the shear resistance of improved steel-asphalt interfaces

Although steel orthotropic deck is currently the most widely adopted solution for long-span bridges, the poor adhesion to the upper asphalt layers still represents a serious problem with a not clear solution. In recent decades many techniques, which involve the use of special bituminous bonding coats, reinforced asphalt membranes, net-reinforced steel deck surfaces or epoxy asphalt binders, have been applied, with varying results, to improve the level of adhesion of the asphalt pavement to the steel surface.
In this experimental study two of such techniques were adopted in order to investigate the shear resistance of steel-asphalt pavement systems. The first technique uses epoxy asphalt both as a bonding coat and as a binder of the upper asphalt layer while the second technique concerns the use of a reinforced asphalt membrane that is applied on the steel deck before overlaying with conventional HMA.
The ASTRA shear test device was used in order to evaluate the shear resistance of different types of HMA-steel interfaces and to investigate the effects of temperature and normal stress. The results have been compared with the shear properties of bitumen-coated interfaces, studied in a previous research.
The results showed that epoxy asphalt guarantees high performance regardless of the test temperature. On the other hand, the shear resistance of the system with the asphalt membrane is lower than with the epoxy asphalt, although it is higher than the resistance of bitumen-coated interfaces at high temperatures.