UFC 3-270-03
15 March 2001
CHAPTER 8
SHAPE FACTORS
8.1. Description. For proper crack sealing, the crack must be routed or sawed to a designated
width and depth for the particular type of sealant employed in the crack repair. The dimensions of
a typical crack reservoir (Figure 8.1.) are defined by a shape factor (S = D/W) that is the ratio of
the depth of the sealant (D) to its width (W). Shape factors generally range from 1.0 to 2.0;
however, these dimensions may be particular for the type of sealant employed in the repair
operation and a recommended value will be supplied by the sealant manufacturer.
8.2. Silicone Sealants. Silicone sealants require a shape of approximately 0.5 (Reference
1.3.3.). For example, if the width (W) of the sawed crack is 1/2 inch (13 millimeters), the depth of
the sawed crack (T) must be 1-1/4 inches (30 millimeters) to accommodate a backer rod of 5/8
inch (16 millimeters). The top of the backer rod will be at 1/2 inch (13 millimeters) below the
pavement surface. This allows for a depth (D) of 1/4 to 3/8 inch (6 to 9 millimeters) of silicone
sealant on top of the crown of the backer rod to keep the sealant at 1/8 to 1/4 inch (3 to 6
millimeters) below the pavement surface.
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