15 March 2001
DISTRESS 70, SCALING, MAP CRACKING, AND CRAZING
12.1. Description. Map cracking or crazing refers to a network of shallow, fine, or hairline
cracks which extend only through the upper surface of the concrete. The cracks tend to intersect
at angles of 120 degrees. Map cracking or crazing is usually caused by overfinishing the concrete
and may lead to scaling of the surface. Scaling is the breakdown of the slab surface to a depth of
approximately 1/4 inch (6.4 millimeters) to 1/2 inch (12.7 millimeters). Scaling may also be
caused by deicing salts, improper construction, freeze-thaw cycles, and poor aggregate. Another
recognized source of distress is the reaction between the alkalies (Na2O and K2O) in some
cements and certain minerals in some aggregates. Products formed by the reaction between the
alkalies and aggregate result in expansions that cause a breakdown in the concrete. This
generally occurs throughout the slab and not just at joints where "D" cracking normally occurs.
Deduct curves for scaling, map cracking, and crazing are shown in Figure 12.1.
12.2. Severity Levels Not Applicable to Alkali-Silica Reaction.
12.2.1. L. Crazing or map cracking exists over most of the slab area; the surface is in good
condition with no scaling (Figure 12.2.). (Note: The low-severity level is an indicator that scaling
may develop in the future. A slab should only be counted if, in the judgment of the pavement
inspector, future scaling is likely to occur within 2 to 3 years.)
12.2.2. M. Slab is scaled over approximately 5 percent or less of the surface, causing some
FOD potential (Figure 12.3.).
12.2.3. H. Slab is severely scaled, causing a high FOD potential. Usually more than 5 percent
of the surface is affected (Figures 12.4. and 12.5.).