| To investigate the effect of different cooling methods on the uniaxial compressive properties of ultra-high performance concrete (UHPC) after high temperature, 45 specimens with dimension of 100mm×100mm×300mm were designed and fabricated. The cooling methods and heating temperature were chosen as test variable parameters. Observe The apparent characteristics, quality loss, and failure mode were observed after different high temperatures and cooling methods. The variation law of compressive strength was analyzed. The experimental results show that as the temperature increases, the surface cracks increase. The mass loss rate increases under different cooling methods. A higher mass loss rate is occured under natural cooling and an approximately linear increase is presented under water cooling. The compressive strength shows a trend of first slightly increasing and then decreasing. Compared with the normal temperature, with the temperature increase, the maximum compressive strength increased by 18.3% and 13.4% respectively under natural cooling and water cooling. When the temperature reaches to 800℃, the compressive strength under natural cooling and water cooling decrease to 20.8% and 18.8% of compressive strength at normal temperature, respectively. When the temperature exceeds 600 ℃, the axial deformation ability of blocks are significantly enhanced. Compared with natural cooling, the peak strain under water cooling develops rapidly, but tends to be consistent at 800 ℃. The peak strain under natural cooling and water cooling increases to 2.22 times and 2.24 times the peak strain under normal temperature conditions, respectively. Compared with natural cooling, the elastic modulus under water cooling is relatively small and undergoes three stages: slow decrease, fast decrease, and slow decrease. Based on experiments, a formula for calculating the residual strength of UHPC after water cooling is proposed, which can provide a basis for evaluating the load-bearing capacity of building after fire. |
