Abstract: An experimental investigation was conducted to identify the characteristics of crack growth in high performance concrete (HPC) subjected to fire, including two parts of work, i.e. crack growth resistance determinations and cracking observations, using concrete of three strength grades 40 MPa, 70 MPa, and 110 MPa. The crack growth resistance curves (R-curves ) of HPC subjected to high temperatures were determined using notched three-point bend beam specimens of 100 mm×100 mm×300 mm. The R-curve (crack growth resistance curve) flattening shows that the crack growth resistance has been significantly reduced by elevated temperature. Concrete with a higher strength grade has a steeper R -curve, with a higher fracture toughness but a shorter critical crack growth. The shorter critical crack growth means that concrete of a higher strength grade has a more brittle behavior. The concrete cracking observations reveal that the consequences of rapid heating are quite different from those of slow heating. For slow heating at a rate of 0.5℃/min, HPC suffered no obvious cracking below 600℃ even if it had a high moisture content. Explosive spalling is an extreme case of the internal cracking driven mainly by vapor pressure. All these results confirmed the vapor pressure mechanism for spalling behavior which should be more significant for denser concrete. The crack growth ranges obtained from the R -curve determination results are in good agreement with those measured in the concrete cracking observations.

Key words: High performance concrete, Fire resistance, Explosive spalling, Crack growth, Vapor pressure