Mechanical characterisation of concrete-asphalt interface in bonded concrete overlays of asphalt pavements

Bonded concrete overlay of an asphalt pavement (BCOA) is a rehabilitation technique consisting of 50-175 mm thickness concrete overlay on an existing asphalt pavement. This technique, known as thin (minimum 100 mm) or ultra-thin whitetopping (thinner than 100 mm) in the past, relies on the composite action of concrete and asphalt layers acting together with a third phase of the system being the interface between the two materials. For this study, the stiffness and strength/fatigue resistance of this interface have been characterised by means of a series of laboratory tests conducted on asphalt and composite cylindrical specimens under different loading and environmental conditions. Testing conditions included wet and dry, and temperatures between 5 and 40 degrees C, a range applicable to BCOA asphalt bases in California. Experimental results from this study indicate the mechanical nature of the concrete-asphalt interface is strongly related to that of the asphalt. The interface stiffness showed clear time dependency, and it significantly softened under wet conditions. Experimental results from this study are in line with common belief that water is one of the critical factors leading to failure of BCOA sections, but do not support the common belief that concrete does not bond well to new asphalt.