Fire resistance of hybrid fibre-reinforced, ultra-high-strength concrete columns with compressive strength from 120 to 200 MPa

This study investigated fire resistance performance for ultra-high-strength concrete (120∼200 MPa) columns incorporating various types of fibres such as polypropylene, nylon and steel. First, 24 small columns were tested with a standard heating curve of ISO 834 for 3 h. The main parameters were the length of the polypropylene fibres and the content ratios of each fibre. In addition, the effects of aggregate types between natural and electric arc furnace oxidising slag aggregates were studied. The fire resistance performance of the specimens was classified by spalling degree, based on the weight loss, the spalling depth and the spalling area. The test results showed that the hybrid fibre reinforcement of polypropylene, nylon and steel fibres were the most effective in spalling protection. After the fire tests on small columns, full-scale columns with compressive strength of approximately 200 MPa were constructed and tested under column loads and subjected to severe fire condition using the ISO-834 fire curve. Superior fire resistance of ultra-high-strength concrete columns was found to be obtained by hybrid fibre reinforcement of 0·2, 0·2 and 0·5 vol.% of polypropylene, nylon and steel fibres, respectively.