15 May 2001
1. GENERAL. Surface treatments consist of a thin layer of aggregate cemented together with an
asphalt (bituminous) material. Surface treatments are widely used because of their low cost and
usefulness in light to medium traffic roadways and parking areas. These treatments are normally used
to seal or waterproof the pavement, provide wear resistance, and increase skid resistance. All surface
treatments are relatively thin coatings of material and do not add structurally to the pavement. Air Force
bases should contact their MAJCOM pavements engineer and Army designer's should contact
the U.S. Army Corps of Engineers Transporation Systems Center (TSMCX) prior to using surface
treatments on airfield pavements, due to FOD potential.
SINGLE AND DOUBLE BITUMINOUS SURFACE TREATMENTS.
a. General. A single bituminous surface treatment (SBST) consists of an application of bituminous
material on a prepared surface followed immediately by a single layer of cover aggregate. Chip seal is a
commonly used term for the same process. Double bituminous surface treatment (DBST) is similar to a
SBST except that two applications of bitumen and cover aggregate are used. The first application of
aggregate uses a coarser aggregate than the second application and usually determines the DBST
thickness. The second application of aggregate partially fills the surface voids and keys into the
aggregate in the first aggregate course. SBST's and DBST's are used on prepared base courses and on
new or old pavements. The DBST's and more additional layers (third or more) are used to provide
greater wearing resistance and some structural strength (minimal).
(a) The functions of the asphalt binder are to hold the aggregate in place, bond it to the
underlying surface, and seal the underlying surface to prevent the entrance of moisture and air. The
binders specified for SBST and DBST are cutback asphalts, emulsified asphalts, and asphalt cements.
The types and grades are shown in table 4-1. ASTM D 1369 also provides a list of binder materials.
(b) The type and grade of binder must be carefully selected. Some items to consider are as
-- Climatic conditions.
-- Curing time of binder.
-- Environmental restrictions.
-- Available materials.
-- Temperature of surface.
-- Condition of surface.
-- Condition of aggregate.