UFC 3-250-03
15 May 2001
CHAPTER 3
SPRAY APPLICATIONS
1. GENERAL. Spray application is a term used to describe many different types of asphalt
applications. More maintenance and repair work for flexible pavements is accomplished by spray
applications of a asphalt material than by any other technique. When properly constructed, asphalt
spray applications are economical as well as long lasting and are beneficial in treating or improving the
pavement condition and increasing the life of the pavement. Where additional thickness is needed to
increase the structural strength of pavements, spray applications are of little help because they
contribute little to the structural strength. The different types of spray applications to be discussed in
detail in this chapter are as follows:
-- Prime coats.
-- Tack coats.
-- Fog seals and rejuvenators (Air Force bases should contact their MAJCOM pavement
engineers prior to using these applications on airfield pavements, due to possible decrease in
skid resistance.).
2.
PRIME COAT.
a. General. Asphalt prime coat consists of a low-viscosity liquid asphalt material applied by a
pressure distributor to an unbound base course before placement of a hot-mix asphalt pavement. The
purposes of the prime coat are to prevent lateral movement of the unbound base during pavement
construction; to waterproof during pavement construction; and to form a tight, tough base to which an
asphalt pavement will adhere. To accomplish these purposes, the prime material must penetrate into
the unbound base and fill the void spaces. A completed unbound base is susceptible to serious damage
from rain, wind, and traffic. An adequate prime coat is insurance against this water and traffic damage.
Prime coat material should be applied to a dust-free unbound base as soon as the base has been
thoroughly compacted and before construction or other traffic loosens surface material in the compacted
base. Sufficient time should be allowed to permit prime material to penetrate thoroughly into the
compacted base. In instances where construction of an asphalt layer is to follow in less than seven days
upon completion of base course compaction, the application of a prime coat may be omitted. When
construction of an asphalt layer will not occur for at least seven days, the compacted base will be
primed. Whether the compacted base is primed or not, the contractor should take steps to protect the
surface from any damage (water, traffic, etc.) until an asphalt layer is placed. Generally, it will take
several days for a prime coat to properly cure and withstand construction traffic and cool or wet weather
may further increase the time required. Construction traffic on an uncured or improperly aged prime
coat can cause more base movement than construction on an unprimed base. Local conditions, local
experience, type of base material, and the type of prime coat material available should all be considered
when deciding on the application of a prime coat.
b. Materials.
(1) Low-viscosity asphalt material should be used as prime material, but the selection of type
and grade must be given special consideration. Some items to consider in selecting the priming material
are as follows:
--
Air temperature.
3-1
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