15 March 2001
A porous friction surface (PFS)
is an open-graded asphaltic concrete wearing
surface containing a large amount of air voids that allow water to drain vertically and laterally
through the pavement structure (Figure 8.1.). These surfaces are usually 3/4 to 1 inch (19 to
25 millimeters) thick and the large void content provides a means to prevent hydroplaning at high
speeds. The surface texture of the PFC provides for excellent skid resistance and decreases the
tire spray under wet conditions. Several procedures to repair a PFS are presented in the
8.2. Sealing Cracks. The guidelines for sealing cracks in a PFS are different from a normal
asphalt surface. The materials used for sealing cracks on a PFS are the same as for a normal
asphalt pavement. The following steps should be conducted for sealing cracks on a PFS.
8.2.1. Prepare the crack. To prepare the crack, all loose material shall be removed and the
crack should be free of dust and dirt.
8.2.2. Seal the crack. The same sealant placement procedures shall be followed as for an
asphalt surface (UFC 3-270-02, "Asphalt Crack Repair"). If the crack is 1/4 inch (6 millimeters)
wide or less, the crack should not be sealed unless loose debris is causing an FOD problem.
Cracks from 1/4 to 3/4 inch (6 to 19 millimeters) should be sealed if they are raveling and causing
an FOD problem. Cracks greater than 3/4 inch (19 millimeters) wide shall be filled with a PFS
asphalt mixture and rolled with a steel-wheel roller. Only seal longitudinal cracks when regular
sweeping methods no longer remove all loose aggregate from the surface. The loose aggregate
could block internal drainage. Transverse cracks should be sealed except those perpendicular to
the water flow. In any case, do not seal the joint if it will interfere with water drainage.