The Performance of Ultra-high Performance Concrete Exposed to 600 ℃ at Early Stage
WU Jiandong1, GUO Liping1,2,3, CAO Yuanzhang1, FEI Xiangpeng1
1 School of Materials Science and Engineering, Southeast University, Nanjing 211189, China 2 Jiangsu Key Laboratory of Construction Materials, Nanjing 211189, China 3 Collaborative Innovation Center for Advanced Civil Engineering Materials, Nanjing 211189, China
Abstract: Ultra-high performance concrete (UHPC) is an advanced cement-based material with ultra-high strength, toughness, and durability, and has been widely used in engineering structures. However, underexposed to high-temperature conditions, UHPC with dense microstructure and extremely low permeability makes it prone to explosive spalling, which in turn affects the service life of the components. In this work, the early mechanical properties and impermeability properties of UHPC were investigated by mixing steel fiber (SF) and polypropylene (PP) fiber, and X-ray diffractometer (XRD), simultaneous thermal analyzer (TG), scanning electron microscope (SEM) and mercury injection (MIP) were utilized to determine the mechanism of UHPC exposed to high temperature at an early stage. The results show that the addition of 0.4% PP fiber can effectively suppress the early high temperature (600 ℃) burst behavior of UHPC; after exposure to high temperature, the mechanical properties of UHPC under steam curing are better than those under standard curing, and compared to properties before exposure to high temperature, the compressive strength and flexural strength loss under steam curing were 15.1% and 30.9%, respectively, while those under standard curing were 18.5% and 26.9%, respectively; the impermeability exposed to high temperature meets the P5 level; steam curing promotes the early internal cement hydration and the pozzolanic reaction of mineral admixtures of UHPC, generating more hydration products, and consuming more free water; in the internal structure of UHPC exposed to high temperature, the pores left by the melting of PP fibers and matrix pores increase to relieve the pressure of water vapor, to prevent UHPC from bursting after high temperature in the early stage.
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2022, Vol. 36 
