15 March 2001
SPRAYED ASPHALT WITH SURFACE AGGREGATE
5.1. Introduction. Single and double bituminous surface treatments (SBST and DBST, respectively)
consist of sprayed asphalt applications followed immediately by one or more layers of aggregate.
These treatments are used to retard deterioration of raveling, improve skid resistance, seal small
cracks, and waterproof the surface. They are usually used on light-traffic roads and overruns.
Another type SBST, sandseal, is also presented. Also, a variational procedure of SBST to repair
bleeding is presented and consists of applying hot sand followed by rolling.
5.2. Single Bituminous Surface Treatment. Bituminous materials which can be used for SBST
are as follows: cutback (RC-250, RC-800, or RC-3000); emulsion (RS-1, RS-2, CRS-1, or
CRS-2); asphalt cement (AC-2.5 or AC-5); or road tar (RT-5 through -12). Aggregate gradations
to be used are shown in Table 5.1.
5.3. Procedural Steps (SBST). The following steps should be conducted for placement of an
5.3.1. Prepare the area. Prior to applying an SBST, all failed areas shall be repaired and
surfaces for treatment shall be thoroughly cleaned. The same procedures for prime and tack
coats should be followed and are discussed in Paragraphs 4.2.1. and 4.5.1.
5.3.2. Apply the binder material. The binder (asphalt material) should be applied with an asphalt
distributor. The distributor must be properly calibrated and the same precautions should be taken
as discussed for sprayed asphalt treatments (Chapter 4). Application rates of the binder and
aggregate for SBST are shown in Table 5.2.