奥村組技術研究年報 No.50 2024 年 9 月■土木系■（構造）Flexural Strengthening of Corrosion-damaged RC Bridge Piers Using
Ultra-High-Performance Concrete Layers: An Experimental Study
Biswas Rajib Kumar＊ Takashi Misawa＊＊ Takahiro Saito＊

OBJECTIVES
Since bridges are important components of social infrastructure, it is necessary to restore the structural performance of RC piers damagedby corrosion without changing their original geometry. As a repair method for deteriorated RC piers, a cross-section repair method wasselected in which the cover concrete was removed and reinforced with UHPC layers containing steel fibers. The purpose of this study wasto verify the effectiveness of this method through experiments with combined axial and reverse cyclic loading.

OVERVIEWThe experimental investigation included five single-shaft RC bridge piers. The
details of the specimen can be seen in Figure 1. Case 1 was a reference or soundspecimen. Case 2&3 underwent an average of 10% rebar corrosion, Case 4&5
underwent an average of 15% rebar corrosion. Case 3&5 was strengthened with 50mm thick UHPC layers. The 28-day compressive and tensile strength of UHPC was
143 MPa and 13.7 MPa, respectively, and the 28-day average compressive andtensile strength of the normal concrete was determined as 25 MPa and 1.7 MPa,respectively. After the fabrication and curing of the test specimens, the accelerated
corrosion test was carried out. Corrosion damage was limited to a height of 600 mm
from the footing surface. The concrete covers in the corroded area were replaced withUHPC layers. The specimens were subjected to reversed cyclic loading with an axial
force of 160 kN. After the application of axial force, the specimens were subjected
to reversed cyclic loading with a drift ratio from 0.25% to 8%. Experimental resultsi.e., envelope curves of applied load vs displacement, ductility, and stiffness
degradation are shown in Figure 2.
(a)Unit in mm(c)(b)

Fig 1: Specimen details

Fig 2: Experimental results (a) backbone curve (b) ductility (c) stiffness degradation

RESULTSThe experimental outcomes showed that reinforcement corrosion considerably reduced maximum load-carrying capacity (MLC). The MLCof the specimen with 15% rebar corrosion was decreased by 9.2%, compared to the reference specimen as can be seen in Figure 2(a).
However, the 15% corroded specimen strengthened with UHPC layers displayed superior structural performance, the MLC was increased
by 24% compared to the sound specimen. The ductility of Case 2&4 was reduced by 14% and 17% when the specimens were subjected to10% and 15% rebar corrosion, respectively. Interestingly, ductility was reduced by only around 7% in the corroded specimens retrofittedwith UHPC layers as shown in Figure 2(b). The magnitude of the stiffness decreased with the increase in deflection as can be seen in Figure2(c). It can be noted that the corroded specimens strengthened with UHPC layers demonstrated remarkably higher stiffness than the soundand corroded specimens. For example, at the deflection level of 3.5 mm, the specimen with 10% rebar corrosion with UHPC layers
demonstrated more than 33% higher stiffness than the sound specimen and the specimen with 10% rebar corrosion.
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