Overview
Recycling of asphalt pavements started more than 20 ago. Actual pavements could have been recycled twice or even more times. On one hand long life time is required for pavements and on the other hand maximum quantity of recycled asphalt pavement (RAP) should be used.
Therefore, the following subjects will be investigated:
- Change of binder properties after several recycling steps
- Change of aggregate shape through mechanical processing (milling).
- Assessment of actual recycling practice, regarding different types of mix plants
- Influence of binder type and rejuvenating agents.
The purpose of this research project lies in the ecological and social need for sustainable pavements and closed cycles of matter.
The goal of the research project is to evaluate a base for the determination of an optimum percentage of RAP in the production of different asphalt mix types making sure that high pavement quality and long term performance is still guaranteed. The reservation against the use of asphalt mixes containing RAP will be reduced by demonstrating that such mixes are still standard conform and well performing.
Testing Methods
- Heat behaviour, resistance to deformation
- Stiffness attempt / module
- Rut test
- Pressure threshold attempt
- Fatigue behaviour
- 4-point bending (SN)
- Low-temperature behaviour
- Train-swell trial
- Aging
- Marshall sample, 120 h / 85 ° C
- Water sensitivity
- Indirect tensile test before / after immersion in water
- Inhomogeneity of the binder
- Thin section examination
Funding
Results
Recycling of asphalt pavements.
First part of research package "Recycling of Reclaimed Asphalt in Hot Mixes"
Technical Implications
Regarding the quality of the mixture, in principle up to 100% RAP can be used in the preparation of mixtures. However, there are requirements which limit the content of recy-cling asphalt pavement RAP. These are mainly the following three:
- Depending on the grading curve of the RAP and the virgin aggregates, the target values for grading may no longer be achieved with high percentages of RAP. In this project, this was the case with the mixture AC 11 S with more than 70% RAP1 0/11.
- With the exception of AC EME mixtures, the use of a rejuvenator is required due to the relatively hard binder in RAP1 and RAP2, if the RAP content exceeds 60 to 70%.
- Heating of the RAP for hot mix production in asphalt plants with a conventional recycling drum is limited to about 135°C and is not possible in plants without a recycling drum. In the cold or batch process, the RAP is added at ambient temperature between 5 and 30°C, depending on the time of year. In the hot process, the RAP is heated additionally, and in the cold process, it is mainly heated indirectly by the hot mineral aggregates, which consequently must be heated to a higher temperature. Hence, the maximum RAP content is limited by the maximum possible mineral temperatures at which no damage is caused to the binder. These limitations do not apply to new 100%-recycling asphalt plants heating the RAP more gently to the required mixture temperature.
Readiness
The results of the whole research package "Recycling of Reclaimed Asphalt in Hot Mixes" bases to implement founded the optimal use of reclaimed asphalt with respect to various aspects of the Swiss Standards.