A chip seal testing device (CTD) capable of applying vertical and horizontal loads and loading frequencies typical of actual traffic is described. The CTD uses a pneumatic system to apply vertical loads up to 1 tonne and a hydraulic actuator to impart horizontal loads (up to 50 kN) at 1.7 metres per second (6 km per hour) - equivalent to 10 percent sideways slippage for a vehicle cornering at 60 km per hour. A number of preliminary experiments using the CTD are described in which seven different binder types (including polymer modified binders) are compared using artificial seals constructed on steel plates with grade 3 aggregate (9.1-13.2 mm). The force required to dislodge a steel disk glued to the chip surface was recorded as a function of displacement. Correlations between the measured peak stress and failure energy and binder properties were poor. This was ascribed to the fact that binders in the seals experienced large finite strains and at effectively a high frequency of loading. A significantly better correlation was found between stiffness modulus and peak stress. Two final experiments illustrate the importance of binder film thickness and substrate surface texture on seal strength. (A)
Abstract