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Journal of the Korea Concrete Institute

J Korea Inst. Struct. Maint. Insp.
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  • Korea Citation Index (KCI)

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Title Evaluation of the Flexural Strengthening Effect of Ultra-High-Performance Concrete (UHPC) on Fire-Damaged Concrete
Authors 유성원(Sung-Won Yoo)
DOI https://doi.org/10.11112/jksmi.2026.30.4.88
Page pp.88-95
ISSN 2234-6937
Keywords 화재손상 콘크리트; 초고성능 콘크리트; UHPC 보강; 휨 성능; 계면 부착파괴 Fire-damaged concrete; Ultra-high-performance concrete (UHPC); UHPC strengthening; Flexural behavior; Interfacial debonding
Abstract This study investigated the applicability of ultra-high-performance concrete (UHPC) as a strengthening material for restoring the flexural performance of fire-damaged normal-strength concrete. The effects of UHPC strengthening thickness, exposure temperature, strengthening configuration, and surface condition on the flexural behavior were experimentally evaluated. Concrete prism specimens were exposed to temperatures of 400, 500, and 600 °C for 3 h, strengthened with UHPC, and subsequently tested under four-point bending. The results showed that the residual flexural strength of the unstrengthened specimen after exposure to 500 °C was 2.63 MPa, whereas the specimens strengthened with 10, 20, and 40 mm thick UHPC layers achieved flexural strengths of 6.16, 10.32, and 19.27 MPa, respectively, corresponding to increases of approximately 134, 292, and 633%. In addition, the flexural toughness increased from 33.96 to 77.84 J as the strengthening thickness increased from 10 to 40 mm. For the specimens strengthened with a 40 mm UHPC layer, the flexural strength decreased from 20.70 MPa at 400 °C to 16.12 MPa at 600 °C, representing a reduction of approximately 22.1%, and interfacial debonding was observed after exposure to 600 °C. The influence of surface condition on the flexural performance was limited because the adopted bonded length was sufficient to prevent premature interfacial debonding. Overall, the results demonstrate that UHPC is an effective strengthening material for recovering the flexural strength and toughness of fire-damaged concrete and that the strengthening thickness is a key parameter governing the flexural performance of the strengthened members.