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When road structures are deteriorating over time, wear and tear is often not restricted to the surface or upper pavement layers. The causes are often to be found in the deeper layers, in particular on roads with high percentages of heavy traffic: The loads applied by heavy truck axles weaken the structure of the road pavement. When that is the case, the base layer has usually lost the stability it needs for shouldering these heavy loads.
Such damage patterns require a rehabilitation method that will restore the bearing capacity. This type of repair is called “structural rehabilitation”. Cold recycling gives roads an almost entirely new chapter in life, while fully re-using the existing material.
Technically speaking, cold recycling is based on the technology of cold milling. The cold recycling operation begins with a milling and mixing rotor milling the damaged road layers to a depth of up to 500 mm. Rehabilitating asphalt roads by means of cold recycling includes the surface course, binder course, and at least part of the base layer.
The reclaimed pavement material is mixed with new binding agents, and with supplementary mineral aggregate if required, by the recycler’s milling and mixing rotor or, in some machine models, twin-shaft compulsory mixer. The binding agents are added in precisely metered quantities by microprocessor-controlled injection systems, which maintain a consistently high quality of the recycled material across the entire stretch to be recycled.
There are two ways of recycling an existing road pavement: The first is effected by a cold recycling train, which completes the entire operation in one single machine pass. The second is effected by a cold milling machine, external recycling of the milled material and placing by a road paver. The first method is called “in-situ”, meaning on site. The alternative method is called “in-plant”, meaning that the material is recycled in a mixing plant which has been set up in the vicinity of the job site.
