Investigation of the early performance properties of a pavement, recycled with foamed bitumen and emulsion through field testing

Abstract

Paper presented at the South African Transport Conference 17 - 20 July 2000 "Action in transport for the new millennium", CSIR International Convention Centre, Pretoria, South Africa. ABSTRACT: The use of foamed bitumen for the modification and improvement of roadbuilding materials is increasing globally. This is mainly due to the increased commercial availability of static and mobile plants with the capacity to produce foamed bitumen following the lapse in patents on the foam nozzle system. As new rehabilitation procedures for maintenance and upgrading of the South African road network such as “In place cold recycling with foamed bitumen” emerge, so a level suitable level of understanding of these processes and reliability in the products requires development. The primary objective of the research was to further the understanding of foamed bitumen treatment. This was carried out by characterising the foamed materials with the same tests as the equivalent emulsion treated materials, which is a better-understood product. In addition to the standard tests, triaxial testing was also carried out on the foamed mix only, as part of a research investigation. Acelerated Pavement Testing (APT) was performed as part of the rutting potential investigation during early strength conditions. It also provided insight into ravelling of foamed bitumen and emulsion treated layers under traffic. The influence of slushing with water or diluted emulsion were investigated and reported. The comparisons between foamed bitumen and bitumen emulsion treated mixes have highlighted the differences between these mixes. Foamed bitumen has provided higher tensile strengths than the equivalent emulsion mix, but higher field compaction results and consequently better rut resistance was achieved for the emulsion treated materials, probably due to a more favourable moisture regime during compaction. The influence of the cement content was not investigated.