The project is designed to assess the effect that changes in durability of road materials due to the inclusion of reclaimed and secondary component materials in the manufacture of new road materials will have on the cost of the construction, both financially and with regard to the environment.
There is a need for engineers, particular the client’s engineers, to understand the full implications of using reclaimed and secondary materials. Whilst efforts to make highway construction more sustainable are laudable, they must be effective over the longer-term and not be just reduced cost and/or environmental impact on the construction phase alone. If the use of such components in the mixtures does affect the serviceability or durability of the mixture, then any savings may be transitory.
The project will build upon existing knowledge, supplemented by limited site and laboratory studies, to develop a specific model to look at this issue and to provide indicatory values for use in the model. The existing knowledge will be extended with an extensive literature search on the times for construction and the relevant effects that determine the service lifetime of the different pavement layers. The site trials will look at mixtures with and without reclaimed asphalt, but will have to assess their durability from early-life properties. The laboratory trials will concentrate on combined effect of ageing and moisture damage on the performance of selected asphalt mixtures containing different proportions of reclaimed asphalt. All three strands will be fed into life-cycle analysis models to customise them for the effect of using alternative component materials on the availability of the network and their overall financial and environmental cost.
The work consisted of a review of existing data on service lifetime and availability of road materials and structures, a site trial to evaluate varying proportions of reclaimed asphalt, experimental evaluation of moisture damage and ageing in asphalt mixtures and development of an impact assessment model. Each of these activities has been undertaken in a co-ordinated manner.
The resulting main findings from the research are:
- The use of lower temperature asphalt systems, reclaimed asphalt, secondary by-products and/or binder additives can have an effect on the durability of flexible pavements, but that affect is not always adverse and may not be great.
- The effect of using lower temperature asphalt systems, reclaimed asphalt, secondary by-products and/or binder additives can be modelled in the expected service life of mixtures.
- Data on the effect of each specific components and the extent to which they are incorporated into the mixture needs to be collected in order to make the model more accurate.
- The MIST procedure is suitable for standardisation as an asphalt conditioning procedure in the EN 12697 series.