Effect of high temperatures on high performance steel fibre reinforced concrete

After being subjected to different elevated heating temperatures, ranging between 105 degrees C and 1200 degrees C, the compressive strength, flexural strength, elastic modulus and porosity of concrete reinforced with 1% steel fibre (SFRC) and changes of colour to the heated concrete have been investigated. The results show a loss of concrete strength with increased maximum heating temperature and with increased initial saturation percentage before firing. For maximum exposure temperatures below 400 degrees C, the loss in compressive strength was relatively small. Significant further reductions in compressive strength are observed, as maximum temperature increases, for all concretes heated to temperatures exceeding 400 degrees C. High performance concretes (HPC) start to suffer a greater compressive strength loss than normal strength concrete (NSC) at maximum exposure temperatures of 600 degrees C. It is suggested that HPC suffers both chemical decomposition and pore-structure coarsening of the hardened cement paste when C-S-H starts to decompose at this high temperature. Strengths for all mixes reached minimum values at 1000 or 1100 degrees C. No evidence of spalling was encountered. When steel fibres are incorporated, at 1%, an improvement of fire resistance and crack [F.M. Lea, Cement research: retrospect and prospect. Proc. 4th Int. Symp. On the Chemistry of Cement, pp. 5-8 (Washington, DC, 1960).] resistance as characterized by the residual strengths were observed. Mechanical strength results indicated that SFRC performs better than non-SFRC for maximum exposure temperatures below 1000 degrees C, even though the residual strength was very low for all mixes at this high temperature. The variations with colour, which occured, are associated with maximum temperatures of exposure. (C) 2006 Elsevier Ltd. All rights reserved.