Effects of chipseal pavement material interactions on flushing

Abstract

Chipseal surfacings are a cost-effective and widely used option for roads having low traffic volumes. Frequent resurfacing is a common maintenance option used on chipseal pavements to maintain skid resistance and prevent moisture damage. The increase in surface thickness, resulting from a build-up of surfacing layers, and excess binder quantities often lead to flushing or bleeding on the pavement surface. Once flushed, maintenance of these surfaces becomes problematic and often full pavement rehabilitation is required. Flushing develops due to the micromechanical interactions between materials within a chipseal layer. In particular, the presence of air voids within a chipseal structure plays a vital role in the extent to which bitumen movement can happen. Thus, a thorough understanding of the mechanistic nature of flushing is essential for better management of chipseal pavements. The reported study was carried out to examine the micromechanical interactions between chipseal layer materials and their relationship to flushing using image analysis techniques. In particular, the effectiveness of using image analysis techniques to analyse the changes in air voids that occur within a chipseal layer during loading were investigated. This study was based on laboratory testing of chipseal pavement cores from in-service pavements from Auckland and Waikato regions of New Zealand. The cores, of 200 mm diameter and thicknesses ranging from 32.4 mm to 44.5 mm, were subjected to lateral cyclic loading and changes to the volume of air voids that had occurred were recorded. Samples from loaded cores were then scanned using a Computed Tomography (CT) scanner to examine the effects of loading on the distribution of air voids. The results from the study showed that image analysis is an effective tool to analyse air voids within a chipseal layer.