INTRODUCTION AND LITERATURE REVIEW
1.2 LITERATURE REVIEW
1.2.2 Rehabilitation / strengthening of damaged RC beam-column joints and connections
1.2.2.3 Epoxy Repairing
Epoxy pressure injection technique has been normally used for repairing moderately damaged RC structures. However, for highly damaged case, partial or total removal and replacement of damaged concrete is required. Usually a high-strength, low or non shrink concrete is used as a replacement materials. Some of the past researches where these techniques were employed are summarizes here.
Popov and Berbeto [1975] presented a comparison of performance of reinforced concrete interior beam-column connections tested under cyclic loading with that of a repaired specimen using epoxy resin. The results showed that the repairing technique could restore
Lee et al. [1980] investigated the effectiveness of repairing of RC exterior beam-column connections. The epoxy injection technique and the removal and replacement technique using with high early strength materials were used to repair the beams of the connections.
They observed that there is possibility of damage moving from the beam to the unrepaired joints and column because of the increase in beam strength due to the use of high strength repair materials. However, the over all performance was acceptable.
Corazao et al. [1988] investigated the effectiveness of different repairing and strengthening techniques in restoring or improving the seismic parameters of RC beam- column connections damaged by earthquake loading. The author concluded that the performance of specimens repaired with epoxy injection rely on the quality of the injection works. Further, the data obtained from testing of a repaired specimen that involved the removal and replacement of the damaged concrete in the joint region demonstrated that the stiffness and strength of the specimen had been completely restored.
French et al. [1990] conducted two test series in order to determine the effectiveness of epoxy techniques for repairing damaged joints. They pre-loaded two interior RC joints and then repaired one with pressure injection and the other by vacuum impregnation.
Their repaired specimens were then subjected to the same load history as that was imposed on the original test specimens. The authors concluded that both techniques worked well in restoring the strength, stiffness, energy-dissipation capacity and the bond.
Authors recommended the vacuum impregnation technique due to its advantage in repairing of larger areas. The epoxy and resin injection techniques are usually employed when the damage level is low.
Beres et al. [1992] tested deficiently detailed, lightly reinforced interior beam-column joints. Methyl-methacrylate resin was used for repairing by vacuum injection. The failure
of the specimens occurred by formation of extensive diagonal crack in the joint along with pullout of the embedded beam bottom bars. The repairing process was capable of restoring 75% of initial stiffness, 72% column shear capacity for the specimen tested by them. There was no change observed in the energy dissipation which was due to reduced rate of strength deterioration.
Filiatrault and Lebrun [1996] tested two one-way exterior beam-column joint, which were damaged by earthquake. One with non-seismic detailing conforming to the construction of fifties and sixties and other following seismic codal details were considered. The specimens were tested by the load history which was imposed on the original structure.
The damaged specimens were repaired by epoxy pressure injection. The authors concluded that the repair procedure was effective in improving the strength, stiffness and energy dissipation.
Karayannis et al. [1998] tested eleven beam-column connections after repairing only with epoxy injection. Their study was focused on the effect of joint reinforcement arrangement on the efficiency of epoxy repair by pressure injection. Though the failure took place by beam hinging, yet the cracks were observed even in the first cycle itself. The authors reported the increase in load carrying capacity and energy dissipation was 8 to 40% and 53 to 139% respectively due to repairing. The change in stiffness varied between a 27%
decrease and a 10% increase. The variations in performance were partially attributed to the variation in being able to inject epoxy successfully into the joint cracks.
Tsonos [2001] repaired two identical half-scale exterior connections by removing the concrete in the entire joint and part of the column end. The removed concrete was replaced with high-strength (70 MPa), non-shrink mortar. Two additional horizontal ties were provided in each specimen. The author observed that the same failure mode
the joint region. The repaired specimens resulted in significant increase in the strength, stiffness and energy dissipation capacity. Finally, author concluded that joint transverse reinforcement might be relaxed with the use of high-strength mortar as a replacement material for the repair of heavily damaged joints.
Shash [2005] reported a case study where the cracks in reinforced beams of a single storey building were repaired by epoxy injection and the effectiveness of repairing was assessed by load test. The cracks were filled by injecting liquid epoxy resin. By performing the load test on the repaired beam the deflection noted was only 2.0 mm, which was less than the allowable deflection of 6.4 mm (as per ACI 318). The author finally concluded that the repaired beam could safely carry the expected loads.
Issa and Debs [2007] tested fifteen concrete cubes for investigating the effectiveness of repairing cracks by using epoxy (Sikadur-52). Out of fifteen cubes cast, twelve cubes were cracked artificially. Six cracked cubes were tested without repairing and rest six were tested after repairing the cracks with epoxy by the method of gravity filling. Three virgin control cubes were also tested (without any crack). The comparison of compressive strength of the tested specimens revealed that the crack resulted the reduction in strength by 40.93% in comparison to control specimen. The repaired specimens also failed to regain the original strength and showed a reduction in strength by 8.23% in comparison to the control specimen.
Karayannis et.al [2008b] experimentally investigated the behaviour of critical external beam-column joints repaired with epoxy pressure injection and further strengthened with carbon-fibre reinforced plastic sheets (C-FRP). The composite sheets were used with the aim to provide a confining system to the damaged concrete. The control specimens were subjected to a single cyclic displacement history so as to induce damage on the specimen similar to that caused by an earthquake. From the observed response of the examined
specimens, they concluded that epoxy resin injection technique was appropriate for rehabilitations of damaged joints, since no damages were observed at the joint area of the specimen after testing of the repaired joint. Further, a combination of epoxy injection with C-FRP sheets led to significant improvement of the load carrying capacity, energy absorption capacity and ductility. Finally it led to improvement on the type of damaged compared with the damage modes of the original specimens.