Sealant shape, particularly for reservoir configurations, also influences performance. It is the primary design consideration and is often dealt with in terms of shape factor. The shape factor is defined as the ratio between the width and depth of the sealant (Peterson, 1982). In direct applications, shape factor is controlled solely by the crack-cutting operation (i.e., cutting width and depth). In backer rod applications, shape factor is controlled by both the cutting operation and the depth to which the backer rod is placed.
Current recommendations for both direct and bond-breaker applications are to give rubber-modified asphalt sealants a shape factor of 1 and silicone sealants a shape factor of 2.Generally, seals with smaller shape factors risk adhesion loss, while those with larger shape factors have increased resistance to adhesion loss.
