Emulsion cold mix asphalt in the UK: A decade of site and laboratory experience

Cold mix asphalt manufactured using bitumen emulsion, by its very nature, has struggled to gain market penetration in the UK due to lack of design guidance and specifications and the need to comply with prevailing hot mix asphalt specification requirements. Despite this, a number of contractors have successfully utilized emulsion cold mix asphalt materials containing recycled asphalt planings on various categories of road. Whilst the majority of schemes in the UK have been on lower category traffic roads, in this paper we discuss the use of one material which has been used on a strategic highway (trunk road) in 2008 which saved 43 t of CO₂ during construction and is still performing well in situ to this day. Site construction details along with an analysis of traffic loading are presented. Laboratory simulations of in-situ curing of material supplied to site demonstrated an indirect tensile stiffness modulus at 10 ℃ of 5 GPa was achieved within 6 months. Binder recovered from site cores was found to be in line with comparable hot mix materials, whilst wheel tracking of site cores demonstrated excellent deformation resistance which has been borne out by site performance over the last decade. The continued development of standards enabling engineers to design and specify cold mix asphalt in the UK is also reviewed.