Performance models for an emulsion-treated material under accelerated pavement testing

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.

During the last 30 years, South African engineers have achieved great success in adding small quantities of bitumen emulsion to gravels of marginal to good quality to provide materials that could cater for the highest pavement design categories. Since the introduction of deep in-situ recycling (DISR) into South Africa, the use of bituminous emulsion and foam bitumen in base layers has become more attractive and the extent of use has been greatly increased. The ageing road network in South Africa, as well as increasing demands in minimum disruption to road users during road construction and rehabilitation, required innovative measures that do not sacrifice the structural integrity of the rehabilitated or newly constructed pavement. The advantages associated with the use of bitumen emulsion include: • The ability to open rehabilitated roads to traffic shortly after construction, thereby eliminating the construction of expensive detours and minimising disruption to road users. • Cheaper construction costs than most standard methods of rehabilitation (World Highways: 2001) • Marginal materials can be utilised in pavement layers. Although emulsion-treated materials have been used with great success for a number of years, their structural performance has not been investigated in detail. Research is currently under way to assess their use in the road building industry. The research includes the use of the Heavy Vehicle Simulator (HVS), laboratory testing and field trials. Results from this research will create a knowledge base on the structural design from which guideline documents and design methods can be developed. The major aspects that are being investigated include: • The engineering properties such as bearing strength, permeability and erodibility. • The mechanical properties such as stiffness, shear strength and strain at break. • The behaviour of the material and pavement under repeated loading. • Aspects that impact on the above such as design, construction and maintenance. This paper discusses the results from HVS and laboratory testing on an emulsion-treated material. The HVS test results were used to determine structural design and performance models for fatigue and permanent deformation for the materials tested. These models were then used to estimate load sensitivity and damage factors.