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Structural Concrete, Vol. 9, no. 4, December 2008

Post-heating bond behaviour between lightweight fibrous concrete and steel

R.H. Haddad, Dept. of Civil Engineering, Jordan University of Science and Technology, Irbid, Jordan
Z.G. Al-Kofahi, Dept. of Civil Engineering, Jordan University of Science and Technology, Irbid, Jordan


The post-heating bond behaviour between fibre reinforced lightweight aggregate concrete (LWAC) and 20 mm-diameter steel bars was experimentally investigated using a modified type of pullout specimen. These were cast using volcanic tuff aggregate concrete with and without hooked steel, brass-coated steel, and a mixture of both types of fibres at a volumetric fraction of 2%, before being water cured for 28 days and subjected to high temperatures, ranging from 300 to 700 C. Standard cubes were also cast, cured and heat-treated under similar conditions before being tested to evaluate compressive and splitting strengths. Duplicate specimens, from various mixtures, were cured in water for a similar period and used as controls. The post-heating cracking pattern and extent were evaluated, and residual strengths and bond behaviour determined and described before and after heating then cooling. The results showed marked reductions in residual bond, compressive and splitting strengths of plain and fibre reinforced LWAC being exposed to high temperatures. Pullout specimens prepared with fibres attained higher residual bond strength and bond ductility after exposure to high temperatures than those of plain ones. The contribution of hooked steel fibres (at volumetric fractions of 1 or 2%) to salvaging bond was over the entire temperature spectrum, while that of brass-coated steel fibres was limited to the lower range of that spectrum (from 300 to 500 C). The findings of the present study confirmed the benefit of using lightweight aggregate in reinforced concrete structures as it contributes to maintaining higher post-heating residual bond strength than that of conventional concrete.

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