Cold in-situ recycling

How does cold recycling work?

In the cold in-place (or in-situ) recycling process, the reclaimed material is not removed from the construction site at all, but is processed and repaved on the spot. This not only eliminates the need for trucks to make frequent trips to a processing facility, but also shortens construction times.

Cold in-situ recycling, one technology with a wide range of uses

As a pioneer in cold recycling, Wirtgen offers a range of technologies and processes that can be deployed to meet the needs of each specific situation. Nevertheless, the underlying technology is the same for all cold recyclers: small amounts of a cement binding agent are spread ahead of the cold recycler, the asphalt layer is granulated to the desired depth, the granulate is mixed with the binding agent and water, bitumen emulsion or foamed bitumen and then repaved and compacted.

Various different use-cases – the difference lies in the paving method:

Projects being realised with a Wirtgen CR series cold recycler usually require the use of an asphalt paver. The homogeneous construction material produced by the cold recycler is transferred directly to the material hopper of the asphalt paver, which then paves it with pre-compaction.

With the WR series of cold recyclers, paving is fundamentally carried out without the need for an additional paver. Before compaction, the material is finely profiled by a Grader.

In a recycling train, all cold recyclers are supplied from a water tanker and, if necessary, emulsion or bitumen tankers driving ahead of the machine.

Paving option – recycling train with a CR series cold recycler

The Wirtgen cold recycler transfers the processed mix directly to the paver’s material hopper for paving. This is followed by compaction.

Paving option – recycling train with a WR series soil stabiliser and cold recycler

The Wirtgen WR cold recycler and soil stabiliser granulates the damaged layers. At the same time, the pre-spread cement is mixed in and bitumen and water are sprayed into the mix. This is followed by compaction.

Foamed bitumen is the first choice as a binding agent in cold recycling

Foamed bitumen is produced by high-pressure injection of small amounts of water and air into heated bitumen. The water then evaporates and the steam produced causes the bitumen to foam up instantly to between 15 and 20 times its original volume. The foam is then added directly to the mixer via injection nozzles and thoroughly blended into the cold and moist construction materials. The quality of the foamed bitumen is primarily defined by the parameters ‘expansion’ and ‘half-life’. This is because the greater the expansion and the longer the half-life, the easier it is to work with the foamed bitumen.

Asphalt rehabilitation with the cold recycling method as a rolling construction site

In many countries around the globe, cold recycling using foamed bitumen as a binding agent has become an established method for the rehabilitation of roads that is increasingly moving into the focus of road construction authorities and construction contractors, and, in some countries, is already the standard procedure offered in tenders. The flexible and enduring layers produced in this way create the perfect foundation for a final asphalt surface layer with reduced thickness. Foamed bitumen is produced from normal bitumen at a temperature of approx. 175 C using state-of-the-art technology. In the in-situ method, the microprocessor-controlled injection systems of the Wirtgen cold recyclers of the CR and WR series inject precisely dosed amounts of the binding agent into the mineral aggregate mix. This means that a project can be realised as a rolling construction site.