Pavement milling

Recycling of the road surface is one of the main reasons for milling a road surface. Milling is widely used for pavement recycling today, where the pavement is removed and ground up to be used as the aggregate in new pavement. For asphalt surfaces the product of milling is reclaimed asphalt pavement (RAP), which can be recycled in the asphalt hot mix asphalt (pavement) by combining with new aggregate and asphalt cement (binder) or a recycling agent. • Raveling: aggregate becoming separated from the binder and loose on the road • Bleeding: the binder (asphalt) coming up to the surface of the road • Rutting: formation of low spots in pavement along the direction of travel usually in the wheel path • Shoving: a washboard like effect transverse to the direction of travel It can also be used to control or change the height of part or all of the road. This can be done to control heights and clearances of other road structures such as: curb reveals, manhole and catch basin heights, shoulder and guardrail heights, and overhead clearances. Specialty Specialty milling can be used to form rumble strips which are often used along highways. Using milling instead of other methods, such as rolling them in, means that the rumble strips can be added at any time after the road surface has hardened. == Types ==

In the USA, the Asphalt Recycling and Reclaiming Association has defined five classes of cold planing that the Federal Highway Administration has recognized. The classes are: • Class I – milling to remove surface irregularities • Class II – milling to uniform depth as shown on plans and specifications • Class III – same as class II with the addition of cross slope • Class IV – milling to the base or subgrade (full depth) • Class V – milling to different depths at different locations == Process and machinery ==

Asphalt milling is performed by construction equipment named cold planers or commonly referred to as milling machines. These machines use a large rotating drum to remove and grind the road surface. The drum consists of scrolls of tool holders. The speed of the rotating drum should be slower than the forward speed of the machine for a suitable finished surface. Modern machines generally use a front-loading conveyor system that have the advantage of picking up any material that falls off the conveyor as milling progresses. Water is generally applied to the drum as it spins, because of the heat generated during the milling process. Additionally, water helps control the dust created. In order to control the depth, slopes, and profile of the final milled surface many millers now have automatic depth control using lasers, string-lines, or other methods to maintain milled surfaces to ± of the target height. == Micro milling ==

Micro milling is also known as carbide grinding. It is a lower cost alternative to diamond grinding of pavement. Micro milling can be used either as the final surface or as a treatment before applying a thin overlay. Micro milling can be used to remove many of the same distresses that standard milling can remove, although usually to a shallower depth. A micro milled surface has a uniform finish with reduced road noise compared to standard milling. == References ==