Evaluation of the mechanical properties of 200 MPa ultra-high-strength concrete at elevated temperatures and residual strength of column

• Mechanical properties of USHC subjected to elevated temperature were evaluated.
• Fire resistance performance of RC column USHC was investigated.
• Prediction process for residual load of column subjected to fire has been proposed.

In this study, material properties of ultra-high-strength concrete (UHSC) and residual load of reinforced concrete column have been evaluated at elevated temperature. On the basis of the results of experiments, prediction process for residual load of column member subjected to elevated temperature have been proposed. For evaluation on mechanical properties at elevated temperature of UHSC, 100 × 200 mm cylinder specimen of 100, 150, 200 MPa was heated to 100, 200, 300, 500 and 700 °C by 1 °C/min. After that, the ratio of compressive strength at room temperature to compressive strength at elevated temperature was measured. Also, comparison evaluation between experimental results of this paper and previously presented properties of compressive strength properties of normal strength concrete (NSC) and high strength concrete was carried out. Reinforced concrete column member was made of 200 MPa concrete and was heated by ISO-834 standard heating curve for 3 h. Internal force degradation and fire resistance performance of column member was evaluated by measuring internal temperature and axial deformation. Also, after heating, residual axial load capacity was evaluated through natural cooling for 24 h. Prediction process of residual internal force of UHSC column was proposed by deriving model for internal force degradation with experimental results of residual mechanical properties and spalling properties of UHSC subjected to elevated temperature. Based on the experimental results, it was observed that internal force degradation of UHSC by elevated temperature occurred more than that of NSC. In the test for fire resistance performance of column, 26% of section was lost due to spalling, however, it was observed that residual internal force was 52% of design axial load.