15 May 2001
(2) Voids in mineral aggregate (VMA). The percentage of the compacted bituminous mixture
not occupied by the aggregate. The percentage of VTM plus the percentage of asphalt cement by total
volume is equal to VMA.
vair % vbitumen
(3) Percent voids filled with asphalt (VF). The percentage of the VMA in the compacted
aggregate mass that is filled with asphalt.
vair % vbitumen
l. Porous friction course (PFC). A porous friction course (PFC) is an open-graded, free-draining
asphalt paving mixture that can be placed on an existing pavement to minimize hydroplaning and to
improve skid resistance in wet weather. The course is placed in a layer usually varying from
approximately 20 to 25 millimeters (3/4 to 1-inch) in thickness. PFC paving mixtures are produced in
asphalt hot-mix plants and placed with conventional asphalt paving machines.
m. Surface recycling. Repaving, heater-planing-scarifying, cold milling, and rejuvenating are
methods of surface recycling that are used to increase skid resistance, decrease permeability to air and
water, and improve properties of the asphalt binder. Depending on the process used, surface recycling
may modify from 5 to 50 millimeters (1/4 to 2 inches) of the pavement surface. Surface recycling, except
for some types of repaving, does not increase the strength of the pavement. The cost to scarify and
rejuvenate pavement is approximately the same as the cost of an additional 25 millimeters (1 inch) of
overlay, but the benefits obtained from the scarification and rejuvenation usually exceed the benefits of
the additional 25 millimeters (1 inch) of overlay.
n. Cold-mix recycling. Cold-mix recycling involves reclaiming most or all of the existing bituminous
pavement by breaking it to a maximum particle size of 4 centimeters (1-1/2 inch), mixing it with virgin
materials, if needed, and reusing the mixture as a pavement material. Cold recycling material can be
used to surface secondary roads, if a seal coat is applied, and as a base course for high-quality
o. Hot-mix recycling. Hot-mix recycling is a process which involves removing the existing hot-mix
asphalt, crushing it if necessary, and mixing it in a hot-mix plant with new aggregate, asphalt, and
recycling agent, when required. The recycled hot-mix asphalt can be designed for use in all types of
pavements. Crushed portland cement concrete has also been used as aggregate for hot recycled
p. Microsurfacing. Microsurfacing is the process of applying a latex modified asphalt emulsion
slurry to an existing pavement surface. The slurry is mixed and applied similar to asphalt slurry seals
except for the specially designed mixing and constant agitation application equipment required by the
latex modifier. Microsurfacing applications can contain larger aggregate particles than conventional
asphalt slurry seals. This slurry can be used as a rut filler or for re-establishing skid resistance. Curing
is normally completed in from 1 to several hours depending on weather conditions.