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Mechanical Properties of High Performance Concrete After Exposure to Elevated Temperatures.


pdf icon Mechanical Properties of High Performance Concrete After Exposure to Elevated Temperatures. (3575 K)
Lawson, J. R.; Phan, L. T.; Davis, F. L.

NISTIR 6475; 39 p. March 2000.

Available from:

National Technical Information Service (NTIS), Technology Administration, U.S. Department of Commerce, Springfield, VA 22161.
Telephone: 1-800-553-6847 or 703-605-6000;
Fax: 703-605-6900.
Website: http://www.ntis.gov
Order number: PB2000-104063

Keywords:

concretes; mechanical properties; exposure; temperature; building construction; explosions; high performance concrete; spalling; structures; environments

Abstract:

This research effort aims to characterize the residual mechanical properties of high performance concrete (HPC) after being exposed to elevated temperatures. Residual mechanical properties of four different types of concrete were measured after being heated to 450 deg C. The average compressive strength for these four types of concrete, before being exposed to elevated temperatures, ranged from an average of 40 MPa (6000 psi) to 100 MPa (15000 psi). Three of the concrete types are high performance concrete (HPC), and one represents conventional normal strength concrete (NSC). The following physical properties were measured for each concrete specimen prior to thermal exposure: physical dimensions, mass, and longitudinal resonant frequency (which allowed for the calculation of Young's Modulus). Before the elevated temperature exposure tests were conducted, a baseline data set was generated for each of the four specimen types after exposure to a nominal room temperature of 25 deg C. Elevated temperature exposures were accomplished by placing the specimens into an electric furnace and heating them at a rate of 5 dec G/min until they reached steady-state condition at one of four selected temperatures. The selected temperatures were 100 deg C, 200 deg C, 300 deg C, and 450 deg C. The controlled furnace temperature rise time plus the steady state heating period produced a total heating period of six hours. Following this six hour thermal exposure and after the concrete specimens cooled in the furnace to room temperature, the specimens were weighed, and the resonant frequency was measured again. The compressive strength and dynamic Young's modulus of each specimen was measured. Results from this study may be useful for accessing post-tire properties of HPC. Explosive spalling during heating was experienced with two HPC types that contained silica fume. This spalling occurred during the release of crystalline, chemically bound, water at temperatures ranging from about 240 deg C to 280 deg C. Explosive spalling was not experienced with either of the concrete mixtures that did not use silica fume.