Repair of thermally-damaged concrete using ultra-high-performance concrete (UHPC) under flexure

초록

Exposure to elevated temperatures significantly degrades the mechanical performance and durability of concrete structures, necessitating effective rehabilitation strategies for thermally-damaged members. In this study, thermally-damaged concrete is strengthened with ultra-high-performance concrete (UHPC) and subjected to four-point loading. A total of 42 specimens, including those not exposed to elevated temperatures, were fabricated and overlaid with UHPC, and their performance is evaluated in terms of UHPC layer thickness (10, 20, and 40 mm), bonded length (100, 200, and 400 mm), surface type (smooth, grooved, and chiseled), and exposure temperature (400, 500, and 600 degrees C), including un-strengthened specimens for comparison. The results indicate that increasing the UHPC thickness significantly enhances flexural performance, achieving up to a 112 % improvement compared to the unstrengthened specimens, primarily due to the superior tensile strength of UHPC. Bond failure is prevented in all specimens except those exposed to 600 degrees C. The strengthening effect exhibits little variation with respect to surface condition, with flexural strength ranging from 19.21 to 21.00 MPa and strengthening lengths of 100 and 200 mm provides only marginal improvement. The experimental results are well predicted using the analytical method, with an average experimental-to-predicted value ratio of 1.11 and a coefficient of variation (COV) of 14.10 %. These findings demonstrate that UHPC overlay strengthening provides a reliable and effective solution for restoring the flexural capacity of thermally damaged concrete members.

키워드