15 May 2001
proper application rate. Generally, the application rate should not exceed that which will allow the
rejuvenator to penetrate the pavement within 24 hours.
(c) The amount of rejuvenator needed to properly modify the asphalt binder may not be the
same amount needed to penetrate the asphalt pavement. The determinations made from the test
sections should dictate the amount of rejuvenator that can penetrate the asphalt pavement, and this
amount should never be exceeded. The optimum benefit will be obtained by applying the maximum rate
that will penetrate the pavement.
(d) When a rejuvenator is applied to the pavement, clean dry sand should be available to
blot areas that received too much rejuvenator. The sand should be evenly spread over these areas,
broomed into a pile, and removed. Rolling the pavement surface 1 or 2 days after rejuvenator has been
applied may help to knead and close hairline cracks.
e. Cold milling.
(1) Cold milling process. The cold milling process can be used to mill a bituminous or portland
cement concrete pavement to a desired grade or depth. The milling machine normally mills up to
50 millimeters (2 inches) of pavement in one pass but can remove up to 100 millimeters (4 inches) ore
more in one pass. The machines can use sensors that follow a stringline grade reference and slope
control to directly control the finished grade. A problem with dust may occur, but this problem is usually
controlled by spraying a small amount of water onto the pavement in front of the machine. The milling
machine can be used during all weather conditions to produce a smoother grade.
(2) Cutting teeth. The cutting teeth on the milling machine are a high maintenance item and
must be replaced often. The teeth may last 1 or 2 days, depending on hardness of the material being
milled and the number of operation hours per day. The cutting teeth can be adjusted to provide a range
of surface textures from smooth to very rough. When all the teeth are in position, the finished surface
texture is relatively smooth. By removing some of the teeth, the surface texture can be made rougher.
When the milled surface is used for a riding surface, a rougher surface texture provides better skid
resistance; however, the rougher surface also causes more tire wear and rider discomfort.
(3) Milled surface. Occasionally, when a pavement surface has been milled, the surface is used
as the riding surface for a period of time. For instance, when a pavement does not have adequate skid
resistance but no immediate funds are available to overlay this pavement, one alternative is to mill the
surface to give it a rough surface texture and provide adequate skid resistance until it can be overlaid or
otherwise repaired. An excessive amount of material should not be removed because the pavement
structure could be weakened. It is recommended that the pavement be overlaid as soon as possible
after the milling. It is recommended that the milled pavement be swept with a power broom to remove
all fines. Otherwise, these fines can collect and be imbedded in the milled grooves making them difficult
to remove later. Raveling after the milling process may become a problem with asphalt concrete
pavements. On airfields, raveling may cause foreign object damage (FOD) to the aircraft. To prevent
FOD, an overlay should be applied immediately after the milling operation.
(4) Milled material. The material obtained from milling operations can be used in pavement
construction. The milled material can be stockpiled, but care must be exercised not to stockpile it too
high, especially in hot weather, since the asphalt concrete material will have a tendency to bond, thus
making it difficult to use. In most cases, the material should not be stockpiled over 3 meters (10 feet).
The milled material can be used for producing recycled cold mix, recycled hot mix, and other mixes.
Occasionally, this milled material can be used to surface secondary roads that otherwise would not be
surfaced. In this case, some additional binder material, such as asphalt emulsion or rejuvenator, is
usually added to rejuvenate the old asphalt or improve binding qualities. This milled material, mixed with