Specification development for cold in-situ recycling of asphalt

In-situ cold recycling provides a valuable means to reduce the environmental impact of road construction. The reduced energy requirements relative to traditional hot mix recycling can lead to significant reductions in cost and associated CO₂ emissions. Worldwide, in-situ cold recycling has been found to be particularly useful in the rehabilitation of rural roads where site locations are far from asphalt plants. However, practical issues remain due to the evolving nature of cold bituminous materials. Unlike hot-mix asphalts which gain strength quickly as they cool, cold-mix bituminous materials gain strength slowly over time. This is particularly an issue in countries with cooler, wetter climates, such as Ireland. Consequently the specification of cold materials poses a number of challenges relating to curing and testing protocols. This paper reports on the development of a specification for cold recycled materials and the application to a case study in Ireland. This work was conducted as part of the CEDR funded project CoRePaSol which focused on the development of harmonised design procedures for cold recycled mixes. In collaboration with the Irish National Roads Authority a 2.5 km site on a national road was identified for a recycling trial. The existing guidance for Low Energy Pavements was used to classify the road with respect to traffic levels and a testing programme was implemented which sought to reflect best practice across Europe. A series of recycling options were assessed and four different mix designs were proposed. These included variation in the binder type (foam mix or emulsion, with or without cement), binder content and recycling depth, reflecting the wide array of options available to engineers seeking to promote cold recycling. Due to the lack of harmonised guidelines across the Europe on design and evaluation of cold mixtures a specific focus is given in this paper to the mix evaluation procedure where alternative laboratory test specimen curing and testing procedures are investigated and recommendations are given.