UFC 3-270-04
15 March 2001
particularly if at a shallow slope, are converted to use as power check pads, extensive thermal
damage can occur. Particular problems are posed by aircraft with vectored thrust such as the
Navy's Harrier or aircraft such as the B-1 or FA-18 with auxiliary power units that exhaust
downward on the pavement for extended periods of time. AFCESA and TSMCX should be
consulted for the most up-to-date guidance on how to deal with these problems.
13.2. Exposure Time and Temperature. Concrete slabs exposed to an ASTM E119 standard
fire for 2 hours indicated that after the temperature of the concrete at about 3/4 inch (19 milli-
meters) below the surface was 1,200 degrees Fahrenheit (649 degrees Celsius), at 1 1/2 to
2 inches (38 to 51 millimeters) it was 800 degrees Fahrenheit (427 degrees Celsius), and at
about 3 1/2 inches (89 millimeters) it was 400 degrees Fahrenheit (204 degrees Celsius). (The
atmosphere temperature for a standard ASTM E119 fire rises to 1,000 degrees Fahrenheit
(538 degrees Celsius) at 5 minutes, 1,700 degrees Fahrenheit (927 degrees Celsius) at 1 hour,
and 2,300 degrees Fahrenheit (1,260 degrees Celsius) at 8 hours.) Normally concrete would not
be exposed to jet or auxiliary power unit exhaust for extended periods of time, and any thermal
damage will be concentrated in the upper surface concrete. Concrete exposed to high
temperatures must be of high quality. It should have a low water/cement ratio, and it must be
properly cured. Leaner concrete mixes perform better than richer mixes. Construction must also
be of high quality. Proper consolidation and proper finishing are critical. Finishing techniques
that cause a paste on the surface will result in scaling. Selection of the proper materials in the
concrete also has a dramatic effect on heat resistance. Aggregate selection probably is the most
important single materials-related factor; however, no standard specification has been developed
for heat-resistant aggregate.
An aggregate with a low coefficient of thermal expansion is generally considered to be desirable,
and one rating system roughly groups aggregates as follows in descending order of desirability
for heat-resistant concrete, as shown in Table 13.1.
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