The re-use of recycled asphalt started in the 1950s. It was spurred on by the energy crisis in 1973-1974 due to bitumen savings and started on a 100% basis in 1976 in the Netherlands. Currently several techniques are available, including batch mixing plant (hot) re-use, drum mixer plant (hot) re-use, plant with parallel drum (hot) re-use and cold mix recycling/re-use.
In Europe more than 300 million tonnes of asphalt are produced at more than 4 000 stationary asphalt plants and 750 mobile plants.
The RE-ROAD project aimed to develop knowledge and innovative technologies for enhanced end of life strategies for asphalt road infrastructures. Such a strategy has an important impact on the energy efficiency and the environmental footprint of the European transport system and fits within the life-cycle thinking which is being introduced in waste policy at European level. It leads to reduction of the need for new raw materials, prevents the creation of waste and the occupation of landfills and consequently minimises the need to transport these materials to and from the work site and hence reducing energy, pollution including CO2 emissions.
The project covered the following issues of reclaimed asphalt:
The impact and potentially adverse effects of different dismantling procedures on the quality of reclaimed asphalt will be investigated.
Improving characterisation of reclaimed asphalt and technical evaluation of reclaimed asphalt as a raw material considering the heterogeneity of the material and the specific industrial process for producing the asphalt mix.
Optimising the process to achieve the highest possible level of quality. Ensuring environmentally sound use of reclaimed asphalt and disposal of materials that cannot be recycled.
Assessment of risks and benefits to the environment with the use of reclaimed asphalt will be developed. Special attention will be paid to potential harmful substances (e.g. tar-containing asphalt). Life cycle analysis (LCA) will be used as a tool for this assessment.
Cost Effective Recycling
Short and long-term performance, as well as lifetime prediction by modelling of asphalt mixes produced with different levels of reclaimed asphalt and production techniques.
Study of the effect on the final asphalt mix quality derived from the specific method for introducing reclaimed asphalt in the mixing plant. Avoiding the problems when recycling polymer modified reclaimed asphalt and how to take full advantage of their special qualities.
The consortium carried out various studies.
Dismantling and Handling Strategies
This dealt with the production of reclaimed asphalt by milling operations and the way milling parameters influence the properties of the reclaimed material. The handling and introduction to the mixing process has been outlined by the project. The mixing plant, as well as limitations and potential problems have been discussed. Furthermore, several case studies have been presented. High levels of recycling can be achieved. However, it is important to avoid any down grading.
Sampling and Characterisation
Details have been provided on a study regarding the sampling of reclaimed asphalt. It turned out that a simplified sampling procedure, with roof-shaped piles and a shovel, is a good alternative to the traditional splitting method. Furthermore, RE-ROAD has presented suitable extraction and recovery methods for reclaimed asphalt. Binder properties play an important rol.
The RE-ROAD project outlined the details of a survey on laboratory mixing practices. The results show differences in everyday laboratory mix design. Some producers do not use laboratory mixing at all. In addition, results showed that laboratory mixing is seldom adjusted to mimic precise conditions at the asphalt plant. Another study has been presented in which different ageing procedures have been compared. It showed that it was possible to restore the initial properties of polymer modified asphalt, even after the material had been aged and recycled three times with a mixing ratio of 1:1 (reclaimed asphalt to new material). Furthermore, mix quality and mix performance have been tested. A number of different laboratory mixing procedures are used in Europe. The study concluded that the differences between these procedures were not significant.
A comparison between different leaching techniques and results from ecotoxicity tests on leachates has been made. Also risk assessment was done with leaching data. Field validation on leaching, showed that there could be potentially high leaching associated with reclaimed asphalt in unbound state. A procedure to study fume emissions that occurs in the asphalt plant and during laying has been presented. Another study used a fume generator, making it possible to make a risk assessment of airborne emissions. It showed that reclaimed asphalt changes the quality of fumes.
Cost effective recycling
The following recommendations for implementation have been
Asphalt is 100% re-usable/recyclable. Road authorities can stimulate recycling as they are the owner and thus also responsible for it. Legislation can also stimulate recycling, as has been seen in the Netherlands.
Innovating for the future (technology and behaviour): Promoting more sustainable development