One technique commonly used in the rehabilitation of roads, highways, and airports is cold planing (CP). Cold planing is the controlled removal of an existing pavement to a
desired depth, longitudinal profile, and cross-slope, using specifically designed equipment. Cold planing can also be used to remove deteriorated, cracked, aged asphalt pavement
or pavement that is unacceptable for other reasons.
The resulting textured surface can be immediately used as a driving surface, can be further treated with one of the other asphalt recycling methods, or once cleaned and track coated, overlaid with hot asphalt (HMA), with or without added RAP. In addition, cold planing can be used to roughen or texture pavements to restore low friction numbers and eliminate slippery surfaces.
The modern cold planer or milling machine has a large diameter rotary cutting drum or “cutter/rotor/mandrel” housed in a “cutting chamber.” The cutter is equipped with specialty designed replaceable
tungsten carbide cutting “teeth” or “tools” that remove or “mill” the existing pavement.
Water is used during the milling operation to control the amount of dust generated and to extend the life of the cutting tools. The water is sprayed onto the tools by a series of spray nozzles that cover the width of the cutting chamber. Milling machines are self-propelled and of sufficient size to provide the traction and stability required to remove the pavement surface to the specified grade and cross-slope. Most machines are equipped with automatic grade and slope controls systems to produce results to the specified elevations and grades.
RAP generated during the cold planning process is loaded onto haul trucks by a conveyor system on the milling machine, and typically is removed from the site. The RAP then is further recycled using Cold Central Plant Recycling (CCPR), Hot Central Plant Recycling, or reused as a base aggregate or similar material is a form of the three “R’s” of recycling (Reduce, Recycle, and Reuse), but the highest-value added application is to use the CCPR process or hot recycled mix.
CP “micro-milling” or “carbide grinding” is a cold planing process that uses a cutting drum equipped with significantly more cutting teeth in order to produce a much finer-textured surface.
Micro-milling’s primary application is for a milled surface that is to be used as the final riding surface without a HMA overlay. Micro-milling can also be used to correct some minor pavement distresses by removing a very thin layer of existing pavement. A surface treatment such as micro-surfacing, thin HMA overlay, chip seal, etc., is then placed as the wearing surface at a significantly reduced cost.
Micro-milling also is used to remove pavement markings due to changing traffic flows or reconstruction. Micro or fine milling can be used to improve pavement skid resistance by removing a small amount of the pavement surface. The resulting surface texture is smooth enough for any vehicle to ride on safely – even motorcycles.
Conventional milling machines are used for micro-milling, so only the cutting drum needs to be changed. The conventional drum on a cold planer has cutting tools spaced approximately 5/8 to ¾ inch (15 to 20mm) apart. This cutting tool spacing produces a grid-patterned textured surface with discontinuous longitudinal striations are much closer together. Other cutting teeth spacing can exist in the range of ¼ to ½ inch (6 to 12mm) apart and is commonly referred to as “fine milling.”
The surface texture, regardless of the type of cutting drum being used, is affected by the condition of the cutting tools, rotational speed of the cutting drum, and the forward speed of the cold planer. The milled surface
has a finer texture when the cutting tools are new, the milling drum rotates faster or the forward speed of the cold planer is reduced.
The same grade and slope controls that are on the cold planer for conventional cold planning are also used during the micro-milling process to ensure that the roadway is re-profiled according to the plans and specification.
Recon currently operates milling machines capable of performing standard milling and carbide grinding/ micro milling. Recon’s milling machines vary in cutting width from 2’ wide up to 10’6” widths.
Recon also offers cleanup crews to perform the detail work around utilities along with the cleanup behind the milling machines.