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Effects of Elevated Temperature Exposure on Heating Characteristics, Spalling, and Residual Properties of High Performance Concrete.


pdf icon Effects of Elevated Temperature Exposure on Heating Characteristics, Spalling, and Residual Properties of High Performance Concrete. (835 K)
Phan, L. T.; Lawson, J. R.; Davis, F. L.

Materials and Structures, Vol. 34, 83-91, March 2001.

Keywords:

heating; spalling; concretes; compressive strength; elevated temperature; high performance concrete; explosive spalling; modulus of elasticity; residual mechanical properties; steady-state test methods

Abstract:

Results of part of an ongoing research program, being conducted at the National Institute of Standards and Technology (NIST) to study effects of elevated temperature exposure on performance of high performance concrete (HPC), are presented. One of the objectives of NIST's research program is to develop a fundamental understanding of the heating characteristics and spalling mechanism in HPC, and to quantify the potential for spalling and the changes in HPC's material properties as a result of high temperature exposure. This paper describes results of NIST's experimental program that focuses on effects of elevated temperature exposure on residual mechanical properties of HPC. Residual mechanical properties were measured by heating the 102 mm x 204 mm cylinders to steady state thermal conditions at a target temperature, and loading them to failure after the specimens had cooled to room temperature. The test specimens were made of four HPC mixtures with water-to-cementitious material ratio (w/cm) ranging from 0.22 to 0.57, and room-temperature compressive strength at testing range from 51 MPa to 93 MPa. Two of the four HPC mixtures contained silica fume. The specimens were heated to a maximum core temperature of 450 C, at a heating rate of 5 C/min. Experimental results indicate that HPCs with higher original strength (lower w/cm) and with silica fume retain more residual strength after elevated temperature exposure than those with lower original strength (higher w/cm) and without silica fume. The differences in modulus of elasticity are less significant. However, the potential for explosive spalling increased in HPC specimens with lower w/cm and silica fume. An examination of the specimens' heating characteristics indicate that the HPC mixtures which experienced explosive spalling had a more restrictive process of capillary pore and chemically bound water loss than those which did not experience spalling.