超高性能混凝土（Ultra-high performance concrete，UHPC）结构致密，高温时易爆裂，从而引起UHPC结构失效和力学性能降低，危害建（构）筑物的服役安全性。为了改善UHPC的耐高温性能，本文采用钢纤维与有机纤维（聚丙烯纤维、聚乙烯醇纤维）混掺来增强UHPC基体，并开展高温试验，测试UHPC试件经历不同高温温度（200 ℃、400 ℃）作用后的质量损失率、残余抗压强度。结果表明：经历200 ℃高温作用后，各组试件均较为完整，但经历400 ℃高温作用后，仅S10P10、S10A10试件的形状保持较为完整，其余试件均发生爆裂；掺入适量纤维可以有效降低UHPC经历高温作用后的质量损失率；经历200 ℃高温作用后，各组试件的残余抗压强度均增大，其中，在混掺纤维组中，试件的残余抗压强度随着有机纤维掺量的增加基本呈降低趋势，但基本仍大于120 MPa，耐高温性能较好。本文研究成果可为UHPC的耐高温性能设计及其在高温服役环境下的建构筑物中的应用提供理论参考。Ultra-high performance concrete (UHPC) features a dense microstructure and is prone to spalling under high temperatures, which consequently leads to structural failure and degradation of mechanical properties of UHPC structures and endangers the service safety of buildings and structures. In order to improve the high-temperature resistance of UHPC, hybrid steel fibers and organic fibers (polypropylene fibers, polyvinyl alcohol fibers) were incorporated to reinforce the UHPC matrix in this study. High-temperature tests were conducted to measure the mass loss rate and residual compressive strength of UHPC specimens after exposure to different high temperatures (200 ℃, 400 ℃). The results show that all groups of specimens remain relatively intact after exposure to 200 ℃. In contrast, only the S10P10 and S10A10 specimens maintain a relatively complete shape after exposure to 400 ℃, while the other specimens all suffer spalling. The incorporation of an appropriate content of fibers can effectively reduce the mass loss rate of UHPC after high-temperature exposure. After exposure to 200 ℃, the residual compressive strength of all groups of specimens increases. Among the hybrid fiber groups, the residual compressive strength of the specimens basically exhibits a decreasing trend with the increase in organic fiber content, yet still remains above 120 MPa, indicating excellent high-temperature resistance. The findings of this paper can provide a theoretical reference for the design of UHPC with high-temperature resistance and its application in buildings and structures under high-temperature service environments.

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