Variable rate bitumen spraying in road construction and resurfacing

Abstract

[Abstract]: Over the last decade, traffic volumes, tyre pressures, wheel loads and the percentage of heavy vehicles using the Australian road network has increased significantly. This has led to increased challenges for road designers to provide economical and durable pavement surfaces with adequate surface texture. A particular solution for improving surface texture on spray sealed surfaces is transverse variable spray rates (TVSR). In this technique bitumen spray-rates are varied across the lane width to account for the impact of traffic in the wheel-paths. This leads to designs where higher binder application rates are used on the shoulders and between the wheel-paths and lower rates in the wheel-paths. An extensive literature review has revealed very little quantitative data has been analysed to verify the technique is beneficial in providing roads with improved and more uniform surface texture. Undesirable surface texture issues generally consist of flushing or bleeding of bitumen in the wheel-paths, and stripping of aggregate between the wheel-paths and on the shoulders. The Queensland Department of Main Roads collects annual survey data of their road network, including surface macro-texture data. This project aims to retrieve and compare survey data over a number of years, and collate it with other relevant data to verify if TVSR technology has provided an improvement in surface texture characteristics. Carefully selected road sections were studied to identify the effect of the TVSR technology when compared with similar areas sprayed with uniform single spray-rates. The study concluded that transverse variable spray rates were successful in increasing the transverse surface macro-texture uniformity of the analysed sections, and when used in conjunction with polymer modified binders, the surface macro-texture depth in the wheel-paths was increased also. Due to the limited scope of the study, further analysis would be required to verify the results across a wider area.