Stress-Strain Relation for Hybrid Fiber Reinforced Concrete at Elevated Temperature
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The presented paper deals with experimental tests and stress-strain relation for hybrid fibre reinforced concrete (HFRC) which contains siliceous aggregates, polypropylene and steel fibres. The main objectives of experimental test is to enhance database of mechanical properties of concrete composites with addition of fibres subjected to elevated temperature as well as to validate general stress-strain relations for conventional plain concrete at elevated temperature when compared with the tested material. Within the experimental study, a unique heat transport test, compressive test and splitting tensile test are performed on 150 mm cubes heated up to 200°C, 400°C and 600°C with the aim to determine a time period for uniform heat distribution in test specimens and mechanical properties of concrete composite, respectively. Obtained findings serve for the development of a material model defined by a stress-strain relation at elevated temperature. Within the process, several models developed particularly for conventional plain concrete during last few years are considered for the validation of their accuracy when applied to HFRC. The presence of polypropylene fibres in concrete matrix is the main reason why the effect of high temperature on the mechanical properties of HFRC is different in comparison with conventional plain concrete. Polypropylene fibres in concrete matrix lower the risk of concrete spalling as the fibres burn fast with increasing temperature due to low ignition point and consequently pore pressure decreases. However, the increase in concrete composite porosity affects the mechanical properties of material, particularly the compressive strength of HFRC decreases more rapidly. As a consequence, the utilization of existing material models for conventional plain concrete at elevated temperature for HFRC is limited.
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