Residual Strength of High-Performance Concrete Subjected to High Temperatures

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Title: Residual Strength of High-Performance Concrete Subjected to High Temperatures

Author(s): N. Gowripalan, P. Salonga and C. Dolden

Publication: Special Publication

Volume: 172

Issue:

Appears on pages(s): 171-192

Keywords: Compressive strength; high-performance concretes; high-strength concretes; temperature; ultrasonic tests

Date: 12/1/1999

Abstract:
High Strength Concrete (HSC) is a subgroup of High Performance Concrete. HSC can be defined as a concrete with a 28-day compressive strength of 50 MPa or more. Concrete structures are designed for fire resistance as given by different fire ratings. It is important to know the residual strength characteristics of a structural material as this will assess the condition of the structure after an accidental fire, continuous high temperature usage and for repairs. In this paper, the residual strength of a HSC mixture containing silica fume is reported. The mixture used in this investigation was a 80 MPa concrete (nominal 28-day compressive strength) and contained 10% silica fume by weight of cementitious material. At the age of 28 days, cylinders were tested for compressive strength and some were placed in a furnace and the heating was applied at a rate of about7 C per minute until the desired temperature was reached. A maximum temperature of 250 oC, 500 OC, 750C or 1000 C was maintained for a period of 3 or 24 hours. The specimens were then allowed to cool to room temperature and tested for compressive strength, splitting tensile strength, modulus of elasticity and ultrasonic pulse velocity. For concrete specimens, heated to 250 OC, a residual compressive strength of 90% was obtained. The drop in the residual strength above 500 C was substantial up to 50%. As the temperature reached 1000 C only about 15% was retained. With the mixture investigated no explosive failure was noticed. It appears that a careful mixture design may eliminate any possible explosive failure. The high temperature effects are more pronounced in tensile strength, modulus of elasticity and ultrasonic pulse velocity. A progressive reduction up to 1000 OC was noticeable in the above parameters. Ultrasonic pulse velocity seems to be useful in assessing the damage of concrete due to high temperatures.