Abstract
Corrosion of steel reinforcement is the major cause of deterioration in reinforced concrete structures. Strengthening of concrete structures has been widely studied. However, most research was conducted on sound structures without considering the effects of corrosion. This paper presents an experimental study of the feasibility of using externally bonded FRP laminates combined with U-jackets, applied directly without repairing the deteriorated concrete cover, to strengthen beams with corroded reinforcement. Ten beams were tested in four-point bending. Two beams were not deteriorated and non-strengthened; these served as references. The other eight were pre-loaded to induce flexural cracks and then exposed to accelerated corrosion. Two of the deteriorated beams were not strengthened, three were strengthened with glass-FRP (GFRP) laminates and three with carbon-FRP (CFRP) plates on the beam soffits. On the six strengthened beams, CFRP U-jackets were installed along the span. Local corrosion levels were evaluated with a 3D-scanning technique. Pitting corrosion significantly reduced the load-carrying and deformation capacity of the deteriorated beams. Despite average corrosion levels of 20%, local corrosion levels up to 57% and corrosion-induced cracks up to 1.9 mm wide, the FRP-strengthening method (applied directly to the beams without repairing the deteriorated concrete cover) was effective in upgrading the load-carrying capacity and flexural stiffness. The applied U-jackets effectively suppressed the delamination of the concrete cover and led to the rupture of GFRP laminates and a utilisation ratio of CFRP plates up to 64%. However, improvement in the deformation capacity was not noticeable; this requires further research.
Highlights
Numerous civil engineering structures are built of reinforced concrete
Previous experimental studies [13,23] showed that merely using externally bonded fibre reinforced polymer (FRP) plates could not effectively increase the capacity of concrete beams with corroded reinforcement; the use of bonded FRPs was limited at failure due to separation of concrete cover damaged by corrosion-induced cracks
The current experimental study investigated the feasibility of using externally bonded FRP laminates combined with U-jackets for flexural strengthening of deteriorated concrete beams with highly corroded steel reinforcement
Summary
Numerous civil engineering structures are built of reinforced concrete. Given the enormous investment made in existing structures, their deterioration poses a major challenge for developed countries to ensure the safety of the aging building stock with limited resources. Previous experimental studies [13,23] showed that merely using externally bonded FRP plates could not effectively increase the capacity of concrete beams with corroded reinforcement; the use of bonded FRPs was limited at failure due to separation of concrete cover damaged by corrosion-induced cracks. Experimental studies [10,13,21] have shown that using externally bonded FRP laminates combined with FRP wraps/U-jackets may effectively improve the serviceability and load capacity of concrete beams with corroded reinforcement. A few experimental studies conducted recently [13,27] indicated that, before bonding the FRP laminates, a patch repair to deteriorated concrete cover might not be necessary, given its limited benefits in terms of improving ultimate load and deformation capacity. The FRP-strengthening efficiency was estimated based on the flexural behaviour of beam specimens subjected to fourpoint bending tests to failure
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