The current South African design practice of cape seals considers the application of single and slurry seals as separate processes. This practice can lead to problems of aggregate overspread, over application of bitumen tack-coat resulting in bleeding, or slurry being over-applied. Subsequently a research project was undertaken to critically evaluate standard design practice. This study concluded that the voids between the single-sized layer of stone are of paramount importance, as they dictate the binder application rate and the quantity of slurry that can be applied without danger of bleeding. The research further aimed at establishing a rational volumetric design method based on the voids between the aggregate. The modified tray test, to determine the effective layer thickness and true void content, forms the basis of the design method. The model mobile load simulator (MMLS3) was subsequently used to evaluate the design prediction (based on volumetric parameters) and the in-service performance of cape seals. From the analysis, criteria were identified and limits proposed to control the combined volumetric composition of the single seal and the slurry components of a cape seal to avoid bleeding. It was confirmed that a maximum total slurry application rate, which avoids bleeding, can be determined. (a) For the covering entry of this conference, please see ITRD abstract no. E127100.
Abstract