Different types of reclaimed and end-of-life material can be recycled in pavement layers. However, these case studies mainly deal with the re-use of pavement materials with an asphalt pavement, a concrete pavement or a road base as its source, or artificial aggregates.
The following terminology is used:
- recycled concrete aggregates (RCA): aggregates from crushing a concrete pavement;
- reclaimed asphalt pavement (RAP): aggregates and bitumen from crushing or milling an asphalt pavement;
- artificial aggregates: limited to the by-product of the metal production industry.
In most cases, the recycled materials are used as inert aggregates. The exception is the re-use of RAP in a new asphalt mix; in this case the available “old” bitumen in RAP can (partially) replace a certain amount of new bitumen. The cement mortar of RCA has still a latent hydraulic potential, but the effect is rather limited.
In most cases a new binder is added. Depending on the application the following binders can be used:
- hydraulic binders: o cement,
- hydraulicroadbinders,
- bituminous binders:
- bitumen, polymer modified bitumen (PmB), etc., o bitumenemulsion,
- foamed bitumen,
- combination of hydraulic and bituminous binders.
The pavement mix with recycled materials should ideally comply with the same performance requirements as mixes with virgin materials, such as stiffness, fatigue properties, compressive strength, etc. A dedicated mix design when using recycled materials is essential. If for some reason it is not possible to reach the same performance, then an adapted road design might be necessary.
We distinguish between where the mixing is carried out:
- in-place – The pavements are milled and without further preparation mixed with the binder and some of new aggregates at the location of the road itself. The recycled pavement material is usually deriving from an asphalt pavement or a road base. The materials from the existing pavement are the main constituents. The add-on material is either spread on the surface of the pavement (e.g. in the case of cement) or pumped into the recycling equipment from a tanker (e.g. bitumen or bitumen emulsion) or generated in the equipment itself (e.g. foam bitumen), and then mixed with the milled materials. Water, if necessary, can be added during the mixing process.
- in-plant – The recycled materials are stockpiled and then processed to obtain an appropriate grading. They are finally mixed in a plant to produce a new concrete mix, an asphalt mix or a cement-treated pavement mix. This mix is transported to the job site and put in place.
This collection reports case studies on:
- recycling in-place using hydraulic and/or bituminous binders, it also addresses the preliminary investigations of the existing pavement prior to recycling it;
- recycling or re-using in-plant where the recycled materials are mixed in plant, adding hydraulic or bituminous binders, to produce a mix for asphalt or concrete pavements, or for road base layers.
Document: USE OF RECYCLED MATERIALS IN PAVEMENTS
Author: Maksym Yaryhin
