Mechanical and fracture properties of normal- and high-strength concretes with fly ash after exposure to high temperatures

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This paper mainly reports an experimental investigation on the residual mechanical and fracture properties of normal and high-strength concrete (HSC) with and without fly ash after exposure to high temperatures ranging from 200 to 600°C. The fracture behaviour of concrete was investigated using the three-point bending notched beam test, according to RILEM recommendations. The effects of concrete strength, temperature level and the presence of fly ash on the fracture and mechanical properties of concrete were investigated. Some studies on the aggregate–cement paste transition zone have been made by means of a scanning electron microscope (SEM). The mechanical properties of concrete specimens significantly decreased with increase in temperature level, the extent of which depended on the presence of fly ash in the mix. In general, fly ash concrete performed better in residual mechanical and fracture properties especially at relatively high temperature levels than concretes without fly ash. Also, fewer and finer microcracks were identified in fly ash concrete under the SEM study.