Guidelines for the mix design and performance prediction of foamed bitumen mixes

Abstract

Paper presented at the 20th Annual South African Transport Conference 16 - 20 July 2001 "Meeting the transport challenges in Southern Africa", CSIR International Convention Centre, Pretoria, South Africa. ABSTRACT: As the use of foamed bitumen mixtures in the road pavements of the Southern African region continues to grow, so the need for sound mix design procedures and performance criteria for these mixes becomes paramount. Four years of fundamental and developmental research into foamed bitumen mixes has been combined with practical experience obtained from laboratory and field application of foamed mixes, as well as previous publications on these mixes, to provide guidelines for their usage. This paper proposes: - methods for the optimisation of the foamed bitumen properties and the setting of suitable limits for its characteristics dependent on type of application, - guidelines for the selection of the ideal aggregate structure for cold foamed mixes including separate filler, sand and large aggregate considerations, - procedures for carrying out cold mix design in the laboratory (including mixing, compaction and curing) - procedures for manufacturing half-warm foamed mixes in the laboratory, - for road structures incorporating foamed mix layers. In particular, the spatial composition of the aggregate plays an important role in determining the behaviour of a foamed mix.To this end,procedures are provided that enable the interaction of moist filler and foamed bitumen to be modelled in terms mastic stiffness as well as optimal blending of aggregate fractions for most suitable foamed mix properties. The proposed guidelines of this paper are pertinent to the Southern African region.They are intended to provide a means of foamed mix selection with improved reliability that is based on sound pavement engineering principles.

As the use of foamed bitumen mixtures in the road pavements of the Southern African region continues to grow, so the need for sound mix design procedures and performance criteria for these mixes becomes paramount. Four years of fundamental and developmental research into foamed bitumen mixes has been combined with practical experience obtained from laboratory and field application of foamed mixes, as well as previous publications on these mixes, to provide guidelines for their usage. This paper proposes: - methods for the optimisation of the foamed bitumen properties and the setting of suitable limits for its characteristics dependent on type of application, - guidelines for the selection of the ideal aggregate structure for cold foamed mixes including separate filler, sand and large aggregate considerations, - procedures for carrying out cold mix design in the laboratory (including mixing, compaction and curing) - procedures for manufacturing half-warm foamed mixes in the laboratory, - for road structures incorporating foamed mix layers. In particular, the spatial composition of the aggregate plays an important role in determining the behaviour of a foamed mix. To this end, procedures are provided that enable the interaction of moist filler and foamed bitumen to be modelled in terms mastic stiffness as well as optimal blending of aggregate fractions for most suitable foamed mix properties. The proposed guidelines of this paper are pertinent to the Southern African region.They are intended to provide a means of foamed mix selection with improved reliability that is based on sound pavement engineering principles.