Repairing Reinforced Concrete Research Articles

Experimental and analytical investigation of RC beams strengthened by ultra-high performance shotcrete

Currently, there is an increasing need for the repair of damaged structures, particularly those situated in confined and challenging locations. Historically, addressing such structures has been hampered by a lack of effective repair and rehabilitation methods. This study aims to investigate, both experimentally and analytically, the application of Ultra-High-Performance Shotcrete (UHPS) for strengthening and repairing reinforced concrete (RC) beams at the bottom. Five RC beams were cast, with one serving as a reference. The remaining four reinforced concrete beams were fabricated with grooved surfaces at the bottom. Subsequently, they underwent strengthening with UHPS at the soffit in two scenarios: one with reinforcements and one without reinforcements. The results indicate a significant enhancement in the load-carrying capacity of the composite beam, up to 126 %, when UHPS is combined with reinforcements. Additionally, the analytical method demonstrates good accuracy, with a maximum error of 16.62 % compared to the experimental results. These findings suggest that the utilization of UHPS effectively improves the structural behavior of RC beams, particularly in challenging locations. Furthermore, the proposed analytical method holds promise for practical application in the design field, offering a systematic approach for implementing UHPS and reinforcements in the repair and rehabilitation of reinforced concrete beams.

Use of Geopolymer and Carbon Fiber-Reinforced Polymer for Repairing Reinforced Concrete Deck Soffit.

This study aimed to assess the feasibility of utilizing geopolymer for repairing reinforced concrete beams. Three types of beam specimens were fabricated: benchmark specimens without any grooves, rectangular-grooved beams, and square-grooved beams. The repair materials employed included geopolymer material, and epoxy resin mortar, while carbon fiber sheets were used as reinforcement in select cases. The repair materials were applied to the rectangular and square-grooved specimens, with the carbon fiber sheets attached to the tension side of the specimens. To evaluate the flexural strength of the concrete specimens, a third-point loading test was conducted. The test results indicated that the geopolymer exhibited higher compressive strength and shrinkage rate compared to the epoxy resin mortar. Furthermore, the specimens reinforced with carbon fiber sheets demonstrated even greater strength than the benchmark specimens. In terms of flexural strength under cyclic third-point loading tests, the carbon fiber-reinforced specimens exhibited the ability to withstand over 200 cycles of repeated loading at 0.8 times the ultimate load. In contrast, the benchmark specimens could only withstand seven cycles. These findings highlight that the use of carbon fiber sheets not only enhances compressive strength but also improves resistance to cyclic loading.

Seismic behavior of damaged RC columns repaired with FRCM composites

In literature, a limited number of studies were carried out on the use of externally bonded composites to repair reinforced concrete (RC) columns subject to cyclic increasing lateral loads. Among them, very few deal with the use of fiber reinforced cementitious matrix (FRCM) composites. Thus, this work experimentally analyzes the behavior of two real scale RC columns repaired through FRCM with carbon fibers, subject both to axial and lateral loads, the latter applied through fully-reversed increasing cycle steps. The goal of the repair interventions was to restore the initial strength and ductility of the specimens after severe damage was applied to the original columns. Two repair methods were adopted: in one case, concrete confinement at the column base was realized; in the second case, other than confining jacket, flexural reinforcement was also used. Cracking pattern, load-displacement curves, ductility, stiffness and strength deterioration, energy dissipation and curvature development along the plastic hinge zone were investigated, comparing the performance of the control specimens with the repaired ones. Results were also compared with ones obtained applying a simple analytical model. Fibers exploitation was experimentally monitored in the repaired columns. Results demonstrate that FRCM confinement jackets can adequately repair seismically-damaged RC columns, restoring the initial lateral load capacity. Repaired columns showed also a similar ductility and energy dissipation compared to the undamaged control ones, while damping ratio resulted slightly lower for the repaired columns.

Structural behaviour of pre-damaged RC columns immediate repaired employing pre-tensioned steel straps

Research focusing on the effects of pre-damaged level on the effectiveness of concrete repairing using external confinement is quite limited. In addition, the use of active confinement in concrete repair works is yet to be explored. This study extends the investigation on repairing reinforced concrete (RC) columns to the active-typed confinement. Experimental tests were conducted to investigate the applicability of active confinement in repairing RC columns with varied pre-damaged levels. The applicability of steel strapping confinement in repairing RC columns with the varied pre-damaged levels was confirmed through experimental works, which involved testing of 21 RC columns under monotonic uniaxial compression. The overall responses of the specimens were investigated in terms of crack pattern, load carrying capacity, axial displacement, stiffness and ductility of repaired columns. The test results have shown that the restorability of confinement was significantly affected by pre-damaged levels. It is also observed that the increase in confining volumetric ratio can restore both strength and ductility of repaired RC columns up to 171% and 172%, for the same pre-damaged level.

The repair of recycled crushed brick aggregate RC beams with shear deficiencies with CFRP

Repairing reinforced concrete (RC) beams using externally bonded carbon fibre reinforced polymer (CFRP) laminate has become one of the main rehabilitation techniques utilised to promote sustainability in construction. The aim of this study was thus to investigate the repair of rectangular simply supported reinforced crushed brick aggregate concrete beams with shear deficiencies in their design. The experimental work consisted of testing twelve full-scale beams (1400 x 200 x 150 mm) under two points load. The specimens were made of normal, and lightweight course aggregate concrete, four beam specimens were used as references, being tested until failure in shear to obtain the ultimate load carrying capacity, while the other specimens were loaded up to 60%-89.4% of the total load at failure, then repaired by wrapping in a layer of CFRP strips in two orientations (90°) and (45°). The variables investigated in this study were therefore the concrete type (normal and lightweight), shear span-to-effective depth ratio (a/d) with two variables (a/d=2.5) and (a/d=3), and the orientation of the CFRP. The results showed that a significant contribution was made by externally bonded CFRP in terms of repairing the beams, which not only refreshes initial shear capacity but also increases the ultimate capacity. The beams showed maximum reliability when the CFRP was oriented at 90° at a ratio of 72%.

Flexural behavior of reinforced concrete beams strengthened with textile reinforced mortar

Textile reinforced mortar (TRM) stands as an alternative for strengthening or repair reinforced concrete (RC) structures. It presents some advantages when compared to other consolidated techniques, however, as an innovative solution, more research and developments are needed. Therefore, this work is an exploratory study using a locally manufactured AR fiberglass textile (TEXIGLASS AR-360-RA-04) to flexural strengthening reinforced concrete beams. The beams geometry consisted of a rectangular section (1500 mm long, 200 mm deep and 120 mm wide) and were subjected to four point bending test. The experimental program investigates the influence of distinct textile layers (2, 3 and 4), age of TRM (3, 7 and 28 days) and the level of beam precracking (no precracking, 50% and 100% of the yielding load) on the flexural behavior of strengthened RC beams. It was mainly found that: (a) all beams presented an increment of ultimate load and the load at serviceability conditions (b) different TRM ages and precracking levels affect the cracking and yielding loads, but no significant influence on the ultimate load; (c) the load-carrying capacity enhances as the number of textile layers increases, as expected. Finally, the results indicate that the tested Brazilian textile has potential to be used in TRM.

Experimental static and dynamic response of RC beams damaged and strengthened with NSM GFRP rod

Inserting FRP rods into grooves using the NSM technique has been demonstrated to be a suitable method for repairing reinforced concrete (RC) beams. There is limited experience with the use of GFRP in the strengthening of RC elements due to low Young’s modulus of glass fibers. The aim of the paper is to analyse the static and dynamic behaviour of RC beams damaged and strengthened by glass fiber reinforced polymer (GFRP) rods utilizing the near surface method (NSM). Undamaged and damaged three RC beams have been experimentally tested under bending loading with and without strengthening by GFRP rods. For a beam, damage has been represented firstly by notches on concrete cover. The beam has been successively strengthened by epoxy resin and NSM GFRP rod and then subjected to bending tests. Vibration tests have been adopted as nondestructive method of control during the experiments to assess the response of RC beams at different damage steps of concrete or due to decrease of bond of GFRP rod. Vibration tests foresaw two boundary conditions, respectively, free-free and hinged ends. Experimental static and vibration results are below shown; discussion and comments on the strengthening bond of NSM GFRP rod have been developed.

Experimental and numerical evaluations on the behaviour of structures repaired using prefabricated FRP composites jacket

Fibre reinforced polymer (FRP) composite jackets have become a popular option for repairing deteriorated structures due to the superior characteristics of composite materials in resisting corrosion and in providing a high strength but lightweight repair system. Recently, a novel prefabricated FRP composite jacket with an easy-fit and self-locking mechanical joining system was developed. This paper presents the experimental and numerical studies on the effectiveness of the FRP jacket in repairing reinforced concrete (RC) columns with simulated corrosion damage under uniaxial compressive loading. The experimental results showed that the jacket successfully stabilised and restored the axial strength capacity of the damaged concrete columns. Moreover, the results of the finite element (FE) analysis revealed that the joint of the jacket should be placed away from the damaged zone to minimise stress concentration and to effectively utilise the jacket as a repair system. Finally, a joint strength of at least 20% of the hoop tensile strength of the jacket is effective in repairing damaged structures.

A new anchorage system for CFRP strips in externally strengthened RC continuous beams

Attaching fiber-reinforced polymer (FRP) strips externally on the surface is a beneficial strategy for retrofitting and repairing reinforced concrete (RC) beams subjected to flexural loading. Despite widespread usage of continuous RC beams, research addressing their performance when reinforced externally with FRP strips is scarce. The loading capacity, moment redistribution capacity, and ductility of FRP strip-reinforced RC members are lower than those of RC beams without FRP strips, due to debonding failures. To avoid early failure in an RC beam reinforced with FRP strips, various anchorage techniques have been proposed. An experimental study was carried out in this research to investigate the flexural performance and moment redistribution capacity of continuous (two-span) RC beams reinforced with carbon fiber-reinforced polymer (CFRP) strips. To avoid untimely failure and improve load-carrying and moment redistribution capacity, as well as ductility, an end anchorage mechanism was proposed. Here, four 6000-mm continuous beams with 250 × 150-mm sections were constructed. The obtained results indicated that utilizing the proposed anchor for the CFRP strips in the continuous beams led to a considerable increase in the loading capacity, moment redistribution ratio, and ductility in comparison with the CFRP-reinforced beams without the anchor. Furthermore, for predicting the load-bearing capacity of a continuous RC beam reinforced using CFRP strips, an analytical model was put forward, whose results showed proper agreement with the test results.

An experimental study on flexural strengthening of RC beams using CFRP sheets

The use of carbon fiber reinforced polymer (CFRP) sheets is becoming a widely accepted solution for strengthening and repairing rein-forced concrete (RC) structures. To date, the behavior of RC beams, strengthened with 60˚ and 45˚ inclined CFRP sheets, has not clearly explained. An experimental program is proposed in this paper to investigate the flexural behavior of RC beams strengthened with CFRP sheets. CFRP sheets were epoxy bonded to the tension face to enhance the flexural strength of beams inducing different orientation angles of 0˚, 45˚, 60˚ and 90˚ with the beam longitudinal axis. The study shows that strengthening RC beams with CFRP sheets is highly influenced by the orientation angle of the sheets. The orientation angle plays a key role in changing the crack pattern and hence the failure mode. The influence of CFRP sheets was adequate on increasing the flexural strength of RC beams but the ductility of the beams was reduced. The best performance was obtained when strengthening RC beam obliquely using 45˚ inclined CFRP sheets where the specimen experienced additional deflection and strength of 56% and 12% respectively and the reduction in its ductility was the least. It is recom-mended to strengthen RC beams, which are weak in flexure, using 45˚ inclined CFRP sheets.

Ductility and Toughness of Unsymmetrical CFRP Strengthening of Reinforced Concrete Beams

The use of externally bonded composite materials such as carbon fiber reinforced polymers (CFRP) sheets is a modern and convenient way for strengthening and repairing reinforced concrete (RC) beams. This study presents experimental investigations on the flexural behavior of reinforced concrete beams strengthened by unsymmetrical CFRP sheets with various configurations. Effects of number of which strengthened faces of strengthening and fiber direction on the flexural strength of RC beams are examined. Six RC beams with dimensions of 100 mm * 220 mm were casted and tested under two points loading. One beam considered as a reference (unstrengthened) beam. Five residual beams were strengthened using CFRP sheets with various configurations. From the results, it was observed that all strengthened beams showed higher ultimate load capacity than that of the control beam. On the other hand, it was found that a progressive reduction in flexural ductility and toughness of beams with strengthening in one face and two faces with horizontal fiber direction. The highest decrease in flexural ductility and toughness for strengthened beams with horizontal fiber direction in comparison to control beam were 63% and 54%, respectively. On the contrary, the flexural ductility and toughness of strengthened beams increased with strengthening by vertical fiber direction. Additionally, the maximum percentage of increase in flexural ductility and toughness were 41% and 54%, respectively in comparison with control beam.

Flexural behaviour of RC beams strengthened with near-surface-mounted BFRP bars

Basalt-fibre-reinforced polymers (BFRPs) are promising economical materials developed in recent years for strengthening or repairing reinforced concrete (RC) structures. The effectiveness of strengthening RC beams with near-surface-mounted (NSM) BFRP reinforcement was investigated in this study. One reference beam and six beams strengthened with NSM BFRP reinforcements were tested under four-point loading. The main test variables were the NSM reinforcement ratio, the tensile reinforcement ratio and the pre-cracking load. The experimental results indicated that, compared with the control beam, both the load-carrying capacity and flexural stiffness of the strengthened concrete beams increased due to use of NSM BFRP bars. For the NSM-strengthened concrete beams, the pre-cracked specimens failed by BFRP bar end cover separation while the directly strengthened specimens (not pre-loaded) were governed by concrete crushing. Analytical models based on the section analysis method were developed to predict the maximum bending moment and ultimate deflection at mid-span of the concrete beams strengthened with NSM BFRP bars. The analytical values of maximum bending moment and ultimate mid-span deflection were in good agreement with the experimental results.

The use of a Phosphate-Based Migrating Corrosion Inhibitor to Repair Reinforced Concrete Elements Contaminated by Chlorides

The use of sodium monofluorophosphate (MFP) was experimented as migrator inhibiting treatment against corrosion of reinforced concrete elements induced by chlorides. The results show that sodium monofluorophosphate, applied by surface impregnation, is able to slow down reinforcement corrosion only for reinforcing steel bars with concrete cover not thicker than 1 cm. This limitation is most probably due to the difficulty, with the type of application adopted, in making MFP to reach concentrations high enough to inhibit the corrosive process at greater depths from the impregnation surface.

Repair of RC bridge columns with interlocking spirals and fractured longitudinal bars – An experimental study

A technique to repair reinforced concrete (RC) bridge columns containing interlocking spirals and having buckled and/or fractured longitudinal bars was assessed through experimental tests. The repair technique involved removing spirals, removing longitudinal bar segments in the plastic hinge region and replacing them with new bar segments that were mechanically spliced to the existing bars with bar couplers, and applying an externally bonded carbon fiber reinforced polymer (CFRP) jacket in lieu of replacing the spirals. Two 1/2-scale prototype bridge columns repaired using two types of mechanical couplers were investigated in this study. The repaired columns were tested under constant axial loading and slow reversed cyclic lateral loading resulting in combined flexural moment, shear, and torsional moment. Test results show that the repair method was successful in restoring the lateral and torsional strength to both columns. The lateral and torsional deformation capacity was restored to one column, while the other was not able to be assessed due to early termination of testing. This study also provides information on the performance of mechanical bar couplers in plastic hinge regions.

Flexural ductility of reinforced HSC beams strengthened with CFRP sheets

Externally bonding fiber reinforced polymer (FRP) sheets with an epoxy resin is an effective technique for strengthening and repairing reinforced concrete (RC) beams under flexural loads. Their resistance to electro-chemical corrosion, high strength-to-weight ratio, larger creep strain, fatigue resistance, and nonmagnetic and nonmetallic properties make carbon fiber reinforced polymer (CFRP) composites a viable alternative to bonding of steel plates in repair and rehabilitation of RC structures. The objective of this investigation is to study the effectiveness of CFRP sheets on ductility and flexural strength of reinforced high strength concrete (HSC) beams. This objective is achieved by conducting the following tasks: (1) flexural four-point testing of reinforced HSC beams strengthened with different amounts of cross-ply of CFRP sheets with different amount of tensile reinforcement up to failure; (2) calculating the effect of different layouts of CFRP sheets on the flexural strength; (3) Evaluating the failure modes; (4) developing an analytical procedure based on compatibility of deformations and equilibrium of forces to calculate the flexural strength of reinforced HSC beams strengthened with CFRP composites; and (5) comparing the analytical calculations with experimental results.

Flexural behavior of reinforced concrete beams externally strengthened with CFRP sheets bonded with an inorganic matrix

Externally bonding fiber reinforced polymer (FRP) sheets with an epoxy resin is an effective technique for strengthening and repairing reinforced concrete (RC) beams under flexural loads. In this study, a total of eight RC beams was tested and analyzed: one control beam and seven beams reinforced with three to six layers of carbon fiber sheets bonded by an inorganic epoxy. All specimens were subjected to a four-point bending test under load control while load, deflection, mid-span strain and failure mode were recorded up to failure. It is found that the load carrying capacity increases with the number of layers of carbon fiber sheet up to 170.2% of the control beam strength. For three and four layers of FRP reinforcement, the beams failed by rupture of FRP, while beams with five and six layers of FRP reinforcement failed by FRP delamination. The ductility of the FRP strengthened beams is greatly reduced compared to the control beam. A moment deflection model is developed and used on the tested beams in current and other similar studies. Good agreement between experiment and prediction values is achieved.

Shear Strengthening of RC Beams with Externally Bonded CFRP Sheets

The technique of strengthening or repairing reinforced concrete (RC) structures with externally bonded steel plates or composite sheets has been successfully applied in civil engineering. The RC structure is often strengthened in flexure. This work studies the effect of the shear strengthening of RC beams on the stress distribution, initial cracks, crack propagation, and ultimate strength. Five types of beams with different strengthening carbon-fiber–reinforced plastic sheets are used. The experimental results show that it is not necessary to strengthen the entire concrete beam surface. The general and regional behaviors of concrete beams with bonded carbon-fiber–reinforced plastic sheets are studied with the help of strain gauges. The appearance of the first cracks and the crack propagation in the structure up to the failure is monitored and discussed for five different strengthened beams. In particular, for one of the strengthened RC beams, the failure mode and the failure mechanism are fully analyzed.

Strengthening of RC beams by using sprayed concrete: experimental approach

An experimental research program was realized to evaluate the effectiveness of repairing reinforced concrete (R.C.) beams with a layer of sprayed concrete. Nine beams (three series) were tested in total. Series one includes the testing of three reference beams to failure. In series two, three beams were loaded, damaged and repaired by the addition of two reinforcing steel-bars and a layer of sprayed concrete then loaded to failure; the beams of the third series were tested in the same manner as in series (2), except that the reinforcing layer was performed with fibrous concrete. In this paper, the results of experimental tests (ultimate load, deflection, longitudinal strains and cracking shapes) are presented and discussed. Then a mathematical modeling is realised to compare theoretical approach results with experimental observations. In the end, conclusions are presented concerning the reliability of this technique and its practical usage.