What effect does long exposure to relatively high temperatures have on the compressive strength of concrete?
Tests conducted on small specimens at the University of Washington showed appreciable strength losses at temperatures over 200 degrees F. Cylinders of 1:2:4 concrete measuring 2 inches by 4 inches were heated for 4 hours 27 days after casting. Compression tests made on the 28th day showed the following percentage reductions for the temperatures indicated: TEMPERATURE REDUCTION 200 18 500 40 800 52 1100 85 1400 96 1700 17 Due to the size of the specimens used in these tests, a much greater surface area was heated in proportion to the mass of the concrete than would normally be true in a structure, and the indicated strength reductions are therefore probably much higher than would occur in a structure. Nevertheless, it seems apparent that major load-bearing concrete elements should not be exposed for long periods to temperatures much above 500 degrees F. There are some indications that the strength reduction can be reduced by increasing the time of curing before exposing the concrete to high temperatures.