The development of structural design models for foamed bitumen treated materials

Abstract

Paper presented at the 21st Annual South African Transport Conference 15 - 18 July 2002 "Towards building capacity and accelerating delivery", CSIR International Convention Centre, Pretoria, South Africa.

The use of foamed bitumen treated materials in the construction of pavement layers is increasing both in South Africa and internationally. These materials are used as a method of cold treatment, and are particularly useful when used in conjunction with the Deep In Situ Recycling (DISR) technology. With the growing need to construct new roads for rural access in southern Africa and to rehabilitate existing roads, these materials are a viable option, because of the many advantages associated with their use, including: • The ability to open the rehabilitated road to traffic immediately after construction, thereby eliminating the need to construct temporary detours and minimizing traffic disruption; • Cheaper construction costs than standard methods of rehabilitation; • Lower quality aggregates can be effectively used in pavement layers when treated with foamed bitumen, and • Environmental savings through the reuse of natural materials. Although foamed bitumen treated materials have been successfully used for a number of years, the structural adequacy of these materials has not been quantitatively proven. Recently, research has been performed to assess the structural performance of foamed bitumen materials. The data used to develop the structural design models were obtained from both laboratory and Heavy Vehicle Simulator (HVS) testing. This paper discusses the development of these models. The paper begins with a discussion on the materials used to generate the data, then discusses the HVS and laboratory tests, and finally, presents the transfer functions. The models were developed from data on one material type and are most applicable to materials similar to this parent material. The models will be calibrated, modified and updated as more data become available.