Wirtgen: Pioneer in Cold Recycling – Gentle to the Environment and Simultaneously Economical

Traffic and heavy-duty transport in industrial countries are constantly increasing. Frequently, road networks can no longer cope with these heavy tonnages and exhibit damage in their lower layers. This is where the cold recycling technology comes in.The method rehabilitates the entire road structure and also increases its bearing capacity on a lasting basis. As a pioneer in cold recycling, Wirtgen is passionately committed to this environment-friendly and economically efficient method. The technological lead we have gained in this complex sector enables us to preserve the functional properties of roads in the long-term.


This method, which is gentle on resources, requires very little new material – indeed, construction materials can be recycled up to one hundred percent. Contrary to conventional methods, costs for transport, storage, removal and disposal are not incurred. Wherever new roads are built, soil stabilizers can be used for efficient processing of the subgrade. Our cold recyclers can also stabilize soils – thus offering contractors an additional source of income.

The operating principle of cold recycling

Cold recycling is an economically efficient and environment-friendly method for producing base layers of superior quality. A distinction is drawn between cold recycling in-situ and cold recycling in-plant.

a) Cold recycling in-situ

When cold recycling in-situ, a cold recycler granulates the existing pavement material while homogeneously mixing in binding agents and water at the same time. This method produces a new construction material mix in just one single machine pass. Cold recyclers are equipped with powerful milling and mixing rotors and with highly efficient injection systems. Some machine models are additionally fitted with paving screeds for placing and pre-compacting the new material mix. This method produces base layers of high bearing capacity.

b) Cold recycling in-plant

When cold recycling in-plant, the damaged pavement material is first removed by a cold milling machine and then transported to a mobile cold mixing plant located in the vicinity of the job site. The milled material is mixed with binding agents in the plant to produce a new cold mix that is suitable for immediate paving.

The key components of cold recycling

Milling and mixing rotor
Cold recyclers granulate the existing pavement material by means of a robust milling and mixing rotor. The rotor is equipped with highly wear-resistant point-attack cutting tools which rotate in special quick-change toolholders. Toolholders and cutting tools are arranged on the rotor in an elevated position, ensuring that the construction material is thoroughly mixed with the binding agents. The engine power is transmitted to the milling and mixing rotor via a direct mechanical belt drive, ensuring maximum efficiency. The design of the cold recycler's drive system with belt pulleys and power belt allows four different rotor speeds to be selected, depending on the intended application.

Mixer

The large cold recycler WR 4200 and the mobile mixing plant KMA 200 produce cold mix in a twin-shaft compulsory mixer. The mixer blends the milled material with water and binding agents to produce a homogeneous mix. The mixing arms and mixing blades, as well as the interior lining are made from highly wear-resistant material.

Injection system for binding agents

The binding agents (cement slurry, bitumen emulsion or foamed bitumen) and water are injected into the cold recycler's mixing chamber via injection bars. These injections bars with pumps and nozzles are precisely adapted to the different types of agents to be added. Metering of the quantities to be added is precisely governed by microprocessor units.

Paving screed

The track-mounted recyclers are capable of placing the recycled mix immediately. A spreading auger distributes the mix evenly across the full working width, followed by the paving screed which compacts the recycled pavement material to produce a compact layer.

The key benefits of cold recycling

Conserve resources:
Cold recycling requires only small quantities of new construction materials, which saves precious natural resources and considerably reduces the number of transports to the job site.

Only one work step
Cold recyclers complete several work steps in one single machine pass: They granulate and remove the existing pavement material, recycle it and then immediately place the new construction material mix. This makes cold recycling an extremely fast-paced method, and the road can quickly be reopened to traffic.

Efficiency
Fast completion, small quantities of new materials required and the small number of transports make cold recycling an economical and environment-friendly method for improving the bearing capacity of damaged road pavements.

Low personnel costs
Cold recycling requires only a small operating crew, for many work steps are carried out by one single machine, resulting in very low labour costs.

Environmentally friendly
Cold recycling saves energy, as the construction materials do not require heating.

Safety
The fast-paced completion of cold recycling projects minimizes disruptions to traffic and reduces the risk of accidents on the job site.