A surface treatment is an application of asphalt
materials to any type of road surface with or without a
cover of mineral aggregate. This application produces
an increase in thickness usually less than 1 inch. Surface
treatments have a variety of uses. They waterproof,
provide a nonskid wearing surface, and rejuvenate an
The simplest types of bituminous surfaces that may
be placed over prepared surfaces are called surface
Surface treatments are applications of
bituminous material to any type of base or pavement
surfaces which, together with an aggregate cover,
produce a pavement with a thickness of 1 inch or less.
In some cases, multiple treatments that produce thicker
pavements are used.
Surface treatments are applied for one or more of
the following purposes:
Waterproof the surface.
Provide a wearing surface.
Make the surface nonskid.
Rejuvenate an old road or runway.
Make permanent improvements.
Surface treatments may be applied to the base
course of a new road or to the surface of an old road as
a method of repair. Surface treatments are grouped into
three categories: sprayed asphalt, sprayed asphalt with
cover aggregates, and asphalt-aggregate mixtures.
Sprayed Asphalt Surface Treatment
Sprayed asphalt treatments contain no aggregates.
They are simply applications of different types of
asphaltic materials to a prepared surface. The categories
include fog seals, dust laying, and road oiling. Prime
and tack coats are also considered as a sprayed asphalt
FOG SEAL. A fog seal is a light application of
diluted slow-setting asphalt emulsion, used to renew
old asphalt surfaces and seal small cracks and surface
voids. Fog seals are especially useful for pavements
carrying a low volume of traffic. A fog seal may also be
used for the following:
1. To seal surface voids in new asphalt plant mixes
2. To prevent dust on sprayed asphalt with cover
aggregate surface treatments
3. To increase aggregate retention
4. To provide a uniform dark color
The asphalt emulsion is diluted with an equal
amount of water, and the diluted material is sprayed at
the ROA of 0.1 to 0.2 gallon per square yard, depending
on the texture and dryness of the old pavement. In
normal conditions, the separation and evaporation of the
water is rapid, permitting traffic within 1 or 2 hours.
DUST LAYING. Dust laying consists of
spraying an untreated surface with a low-viscosity liquid
asphalt, such as SC-70, MC-30, MC-70, or a diluted
slow-setting asphalt emulsion. The asphalt and dilutant
penetrate and coat the fine particles and temporarily
relieve the nuisance of dust.
The material is sprayed at a ROA of 0.1 to 0.5 gallon
per square yard. When emulsion is used, it should be
diluted with 5 or more parts of water by volume.
Diluted emulsion dust-laying treatments usually require
several applications. The dust stirred by traffic between
applications eventually conglomerates and no longer
rises. This is an effective treatment in a very dusty
environment where one application of asphalt is
ROAD OILING. Road oiling differs from dust
laying in that it is usually accomplished as part of a
planned buildup of low-cost road surfaces over several
years. Each application may be mechanically mixed
with the material being treated, or it maybe allowed to
penetrate. The light oils in the road oil penetrate into the
subgrade and tend to repel moisture absorption. The
objective in all road oiling work is to form a dustless
wearing surface, combined with a strong
Because soils vary widely, procedures for oiling are
a matter for local trial and error, rather than scientific
analysis. The amount of road oil, required in the first
year of work will vary from 0.75 to 1.0 gallon per square
yard. The first application is applied at the ROA of
about one half of the total; succeeding applications are
made in equal amounts.
Road oiling treatments are placed several weeks
apart, depending upon the character of the asphalt soil
mat. If some breakup occurs after the first winter, light