A new quantitative method of assessing fire damage to concrete structures

Abstract

This paper describes a laboratory investigation into the adoption of the stiffness damage test to assess fire-damaged concrete structures. Laboratory-prepared concrete cores (75 mm diameter, 175 mm long) were fired under different heating regimes and their uniaxial compression stress-strain response at low stress level was determined. The area of hysteresis of the load-unload loops and other characteristics of the response such as the degree of concavity, the loading chord modulus, the unloading modulus and the residual plastic strain provide a quantitative measure of the extent of structural damage caused by thermal exposure. Fire-damaged specimens were also monitored by measuring the ultrasonic pulse velocity. The microstructure of the damaged specimens was studied using scanning electron microscopy (SEM) and X-ray diffraction. 320°C marked the onset of significant modification in the characteristics of the stress-strain response loops, with a sudden increase in the damage index (area of hysteresis loops). The ultrasonic pulse velocity in the fired concrete showed similar variation with temperature to that of the elastic properties. At temperatures higher than 320°C, SEM photographs showed significant cracks in the cement paste, especially in the interfacial zone.

Evaluating residual compressive strength of concrete at elevated temperatures using ultrasonic pulse velocity

“…The use of ultrasonic pulse velocity (UPV) for assessment of concrete residual strength is one of the most interesting subjects in the field of nondestructive testing of concrete after exposure to high temperatures. Several experimental studies had been carried out to investigate how the pulse velocity was affected by the damage of concrete caused by various high temperatures [6][7][8][9][10].…”

High Strength Concrete Tests under Elevated Temperature

“…Among these early studies were mostly material tests (Felicetti et al 1996, Furumura et al 1995, Sullivan and Sharshar 1992, Hammer 1995, Diederichs et al 1988, Hertz 1992, Hertz 1984, Castillo and Durrani 1990 and element tests (Diederichs et al 1995, Hansen and Jensen 1995, Sanjayan and Stocks 1993, Shirley et al 1988). There were also some other early studies that adopted different techniques, for instance, the scanning electron microscopy and stiffness damage test to evaluate the properties and behavior of HSC at elevated temperatures (Lin et al 1996, Nassif et al 1995. Castillo and Durrani (1990) investigated the compressive strength and loaddeformation relationship of HSC exposed to high temperature by conducting stressed and unstressed tests on cylinders made of high strength and normal strength concrete mixtures.…”

Hydration Kinetics and Fire Resistance of Recycled Low Grade Alumino-silicate Refractory Bricks Waste-metakaolin Composite Cement Pastes

“…The specific gravity of ASRBs and MK is 2.96 and 2.65 g/cm 3 , respectively. Figure 15 shows as C-S-H, C-A-H and C-A-S-H phases deposited in the pore system and also as a result of internal autoclaving effect [44]. The compressive strength of composite cement pastes start to decline at 450 o C, which may be due to the dehydroxylation of the Ca(OH) 2 producing CaO and H 2 O.…”