In situ pavement recycling

Description

Recycling of pavements is a technique whereby an existing degraded pavement is modified and transformed into a homogeneous structure that can support the traffic requirements. More specifically, it involves reusing the materials from the existing pavement for the construction of a new layer, including:

• pulverisation of the existing pavement up to a certain depth, and
• addition of a binder (cement or hydraulic road binder, sometimes combined with bituminous emulsion), water (for hydration, mixing and compaction), aggregates if necessary (for grading correction or other purposes), and admixtures. Mix design is based on the results of performance tests on trial mixes.

Most often, these operations are performed in-situ.

The homogeneous mixture is compacted and cured appropriately, resulting in a base or a layer with a satisfactory structural contribution to a new pavement.

A sealing coat is then applied on the recycled layer to protect it against traffic during the works, with one or two layers of asphalt concrete later applied to ensure the functionality and bearing capacity of the pavement.

Using cement bound recycling, a homogeneous and stable layer of an adequate thickness to be obtained, with mechanical characteristics similar to those of a soil/cement or a cement-bound base.

Therefore, with cement bound recycling the bearing capacity can be substantially increased or, conversely, pavement deflections, subgrade stresses and strains can be greatly decreased. Moreover, existing ruts can be appropriately corrected if the thickness of the bound layer is increased.

Advantages

Recycling of a pavement in place leads to:

• re-use of old, polluted or inadequate materials in the existing pavement,
• uniformity of the pavement, both in strength and in geometry,
• reduction in waste and extraction of aggregates from quarries or pits, with the associated environmental advantages,
• the possibility of repairing individual lanes of roads with two or more lanes, where deterioration is frequently restricted to those supporting the heaviest traffic,
• decrease in nuisance caused by conventional repair work traffic,
• lower risk of causing deterioration in the adjacent network of secondary roads as a result of the reduced volume of new materials to be transported,
• lower costs of renewal of worn pavements,
• maintenance of the surface to a level which will not need hard shoulders and curbs to be raised, and will not reduce the clearance under bridges,
• opportunities for simultaneously widening the existing road, a frequent situation when upgrading a road. The construction of narrow wedges often associated with the widening can be avoided.

Applications

Pavement recycling is used for a number of applications, from heavy traffic motorways to low volume roads. Airport pavements have also been constructed with recycled pavement materials and cement.