The use of recycled aggregates in slag bound mixtures

摘要

In the UK, bound sub-base and/or base usually comprise virgin aggregates with bitumen or Portland Cement as a binder. Production of these binders is energy intensive and use of alternative "secondary" binders could realise considerable cost and energy savings during road construction. Alternative hydraulic binders exist but their use in the UK is currently limited. Granulated blast furnace slag when activated with lime, or lime based material, demonstrates cementitious properties and can act as a binder for any suitable aggregate to form "slag bound material (SBM)". SBM is widely used throughout Europe for sub-base and base layers in the construction of all categories of road. SBM is a cold mix/cold lay material which develops a high level of stiffness and strength compared to conventional bituminous mixtures and similar level of performance to cement bound materials, but at a slower rate. Whilst numerous studies have demonstrated the potential of SBM using natural or slag aggregates, there appears to be little if any previous research looking at the use of recycled fine aggregates generated by highway and utility arisings. This paper presents the results of a series of laboratory tests obtained on selected mixtures of SBM utilising recycled aggregates. Effects of mix design on the early life strength and longer term strength development have been investigated and the results are compared to a conventional mixture utilising natural aggregates. The paper concludes by suggesting optimised mix design for recycled aggregates with high levels of performance.