Post-Fire Flexural Tensile Strength of Macro Synthetic Fibre Reinforced Concrete

Abstract

Tensile cracks in plain concrete occur and propagate when the tensile stress exceeds the bond strength of the cement. These cracks are generally bridged by coarse aggregates however the inclusion of fibres in concrete provides significant additional crack bridging. The utilisation of fibres in concrete has been extensively researched however most studies have focussed on steel fibre or newer types of fibre including glass, basalt and carbon. Current Australian and international design standards do not address the loss of strength for macro synthetic fibre reinforced concrete after exposure to elevated temperatures. This paper is an experimental study of the post-fire performance of macro synthetic fibre reinforced concrete. The flexural performance of the concrete is determined by performing 4-point bending tests on prisms after being heated in a furnace. Specimens were exposed to temperatures up to 800 °C. It was observed that the addition of macro synthetic fibre in concrete has a negligible effect on the overall peak cracking load of the specimens. The significant benefits of fibres are seen after the onset of cracking as the fibres hold the crack together which allows the specimen to withstand greater deflections and achieve a high residual strength. After exposure, the specimens displayed post-cracking flexural strengths between approximately 2–3 MPa for temperatures ≤600 °C. The specimens with 0.8% fibre displayed much higher strengths than the specimens with 0.4% fibre for temperatures ≤400 °C. However, for strengths after exposure to 600 °C and 800 °C, far less variance was observed.