Quantifying the Effects of Chip Seal Volumetrics on the Occurrence of Pavement Flushing

Abstract

The reported study was undertaken to investigate the micromechanical interactions that occur between sprayed seal (chip seal) layer materials in order to examine their relationship to the initiation of flushing. In particular, the deformation patterns of chip seal pavement samples with respect to lateral cyclic loading as well as the changes that occur to the distribution of air voids within a chip seal layer during loading were investigated. The effect of binder volume and air void volume on the development of flushing of the chip seal samples was also investigated. The reported study was based on laboratory testing of chip seal pavement samples (cores) that were obtained from in-service, flushed pavements in New Zealand. The cores, of 200-mm diameter and thicknesses ranging from 32.4 to 55.5 mm, were subjected to varying levels of lateral cyclic loading using a wheel tracking machine and the deformation that had occurred on the surface of the cores was measured. The cores were then scanned using a computed tomography (CT) scanner to examine changes that had occurred to the air void volume of the cores during the wheel tracking test, and the reductions in air void volume were compared with the quantity of flushing that was displayed on the cores. The cores were tested to determine the binder volumes in order to investigate how flushing development was affected by the ratio of binder volume and air void volume. The results from the analyses demonstrated that a strong correlation existed between flushing and air void volume reduction, where a larger reduction in air void volume directly corresponded to a higher amount of flushing. The deformation pattern of the cores indicated the likely state of stability of the chip seal structure, and the state of stability in turn indicated the best method of maintenance that was required for a flushed surface. The study findings demonstrated that the combination of wheel tracking and CT scanning is an extremely effective analysis method that can be used to determine the state of stability of a chip seal and to select the best maintenance treatment for pavement flushing.