Technology

Governments and industry members are increasingly recognizing the value of the material existing in roads and highways. Consequently, they are turning to pavement preservation programs, which include maintenance strategies and rehabilitation treatments to enhance pavement performance as well as extend pavement life in a cost-effective and efficient manner.

Various asphalt-recycling techniques have been developed that prolong pavement life and reduce costs. One such method is hot in-place recycling, or HIR, which can save up to 35% in cost and 50% in time while conserving non-renewable resources.

AR2000 Hot-in-Place Recycling System

heaterA patented circulative heating system combining forced hot air with indirect low-level infrared heat is incorporated into each unit of Martec’s AR2000 Super Recycler train. Air is heated to 600ºC in a diesel-fueled combustion chamber and jets of high-velocity hot air are blown onto the pavement through thousands of small holes in a heating plenum. Hot air is vacuumed for reheating.

The AR2000 Super Recycler’s heating system does not overheat the bitumen, and its three milling drums loosen and remove softened pavement without breaking the aggregate. An automated depth-control feature permits asphalt removal to depths of 50 mm or more in one pass and the milling drums can be adjusted to handle working widths ranging from 3.2 to 4.0 m.

To meet client specifications for the pavement quality, corrective material can be added to the reclaimed asphalt pavement (RAP). A patented Postheating, Drying and Mixing Process ensures thorough heating of the RAP and added material and removes moisture. The mixture is then picked up by a slat conveyor and transferred to an onboard twin-shaft pug mill for final mixing before laydown and compaction by a conventional paver and rollers.

Asphalt Recycling Techniques

The Asphalt Recycling and Reclaiming Association (ARRA) has defined several broad categories of asphalt recycling methods, each of which have differing purposes but which may sometimes be used in combination. For more detailed information on the following definitions, please refer to ARRA.

Hot In-place Recycling

HIR is an on-site method of rehabilitating deteriorated asphalt pavements to a typical depth of between ¾ to 2.5 inches (20 to 60 mm) by applying heat to soften the surface layer of the pavement, or wearing course. The softened asphalt material, which is loosened and removed by milling devices, is mixed together with or without the addition of a recycling agent such as Cyclogen L. This mixture is then spread on the roadway and compacted to complete the recycling process. This method of 100% recycling can be quite effective; however, new hot-mix asphalt or aggregate materials may be added for structural correction and upgrading. Admix can be added to increase the thickness of the wearing course.

Cold In-place Recycling

CIR is an on-site process of rehabilitating asphalt pavements to a typical depth of between 2 to 4 inches (50 to 100 mm) without the application of heat. Depths of 5 to 6 inches (125 to 150 mm) are possible with the addition of chemicals. It is a method in which old asphalt cement is pulverized to a precise depth, mixed with a liquid binder and repaved to an accurate grade and profile. Except in cases of rural roads with light traffic flow, CIR requires that a new wearing course be applied over the recycled material.

Full-depth Reclamation

“FDR is the rehabilitation technique in which the full thickness of the asphalt pavement and a predetermined portion of the underlying materials (base, subbase and/or subgrade) is uniformly pulverized and blended to provide an upgraded, homogeneous base material. FDR is performed on the roadway without the addition of heat, similar to CIR. Treatment depths vary depending on the thickness of the existing pavement structure, but generally range between 4 to 12 inches (100 and 300 mm).” (ARRA, Basic Asphalt Recycling Manual, p.16)