Rehabilitation Of Concrete Structures Research Articles

Experimental and Numerical Investigation of the Seismic Performance of RC Moment Resisting Frames

The rehabilitation of concrete structures has been a subject of extensive investigation, exploring various facets. One such avenue involves the incorporation of fiber additives into concrete materials. In parallel, the construction of reinforced concrete structures inevitably encounters construction errors, necessitating constant efforts from researchers to devise solutions for mitigating their impact. In the context of this research, a series of experiments was conducted involving the construction and testing of five reinforced concrete moment-resisting frames. The initial sample served as the control, while two additional samples were integrated with polypropylene and metal fibers. The subsequent two samples deliberately introduced a manufacturing error through the application of air-entraining admixture materials at the beam-to-column connection. This deliberate error aimed to assess the influence of additive fibers on frames affected by manufacturing errors. Several critical parameters were subjected to evaluation, including ultimate strength, stiffness, ductility, energy dissipation capacity, and strength reduction factor. The results of these assessments demonstrated that the utilization of additive fibers contributes to an enhanced overall performance of the frames, as inferred from the aforementioned seismic parameters. Furthermore, it was established that the incorporation of these additive fibers substantially alleviates the impact of manufacturing errors on moment-resisting reinforced concrete frames. Although a significant reduction in energy dissipation capacity was observed in samples with manufacturing errors, the other seismic parameters remained relatively unaffected. Subsequently, numerical models were generated in ABAQUS software to validate the experimental findings, and their outcomes were compared with the results derived from the physical experiments.

Potential utilization of sugarcane bagasse ash in cementitious composites for developing inorganic binder

The sugar industry uses raw bagasse to generate electricity and subsequently produces tonnes of bagasse ash annually. This bagasse ash is dumped into a landfill, causing an adverse effect on the ecosystem. Sugarcane Bagasse Ash (SCBA) has gained widespread acclaim due to its sustainability and ease of use as a Supplementary Cementitious Material (SCM). SCM has been successfully used in concrete structures, but they are rarely used for the rehabilitation of concrete structures. This investigation's primary goal is to evaluate the mechanical strength of cement mortar which contains Sugarcane Bagasse Ash and Silica Fume (SF), to serve as an inorganic binder for the fabric-reinforced cementitious matrix (FRCM). Analysis using X-ray diffraction (XRD) and X-ray fluorescence (XRF) revealed the existence of amorphous and crystalline phases with silicon dioxide, which was identified as making up more than 70% of the sample. The scanning Electron microscopic (SEM) examination divulges the appearance of fibrous and tetrahedral shape in SCBA, which signify the presence of quartz mineral. The cement mortar was prepared by partially substituting cement with SCBA in a ratio ranging from 0% to 30% by weight and silica fume (SF) at a rate of 5% and 10%. Mechanical strength tests results exhibit that after 28 days of curing, the strength of cement mortar containing 10% SCBA and 10% SF was increased by 2.65% and 5.73%, respectively. A regression analysis was performed to derive a mathematical expression for the prediction of mechanical properties of mortar. This expression provides a high correlation to predict the strength with different mix proportion ratio.

INNOVATIVE USE OF SHAPE MEMORY ALLOYS AS REINFORCEMENTS FOR CONCRETE BEAM-COLUMN JOINTS: AN OVERVIEW

Shape memory alloys have two unique properties of shape memory effect (SME) and superelasticity (SE) that are the ability for large inelastic deformations recovery after heating (SME) and stress removal (SE). In recent years, structural engineers used these materials in the field of civil engineering’s, such as the applications of SMAs in the repair, retrofitting, and rehabilitation of concrete structures, dampers, vibration isolation systems, vibration control, and prestressing members, etc. To overcome and reduce the potential seismic risk of structures, understanding the characteristics of SMAs materials under different loading conditions is one of the critical steps. Despite the various types of researches carried out on the SMAs' structural applications, there was a need for a review of the progress of the current method in structures. To address it, a brief review of the applications of SMAs in Reinforced Concrete (RC) beam-column joints was conducted.

A State-of-the-Art Review of Electrochemical Chloride Extraction for Concrete Structures

Electrochemical chloride extraction is a promising technique for the rehabilitation of concrete structures under chloride induced corrosion. This study consists of an extensive literature review of this treatment including application cases. It is found that the rate of chlorides removed is affected by the total charge passed, whereas increasing charge in a range between 1500 to 2000 Ah/m2 increases the amount of chlorides removed and this can be more effective by increasing current density instead of duration of treatment. Bound chlorides are extracted during treatment and, water works better than Ca(OH)2 as an electrolyte, possibly due to modifications on the concrete pore structure. Moreover, ECE is not efficient in repassivate structures but is efficient in its purpose of removing chlorides if treatment setup is well planned, which justifies the need for better international standards on the topic.

Quality Assessment of a Novel Camera-Based Measurement System for Roughness Determination of Concrete Surfaces-Accuracy Evaluation and Validation.

The roughness of a surface is a decisive parameter of a material. In rehabilitation of concrete structures, for example, it significantly affects the adhesion between the coating material and the base concrete. However, the standard measurement procedure in construction suffers from considerable disadvantages, which leads to the demand for more sophisticated methods. In a research project, we, therefore, developed a novel camera-based measurement system, which is customized to meet the prevailing requirements for practical use on construction sites. In this article, we provide an overview of the measurement system and present comprehensive examinations to evaluate the accuracy and to provide evidence of validity. First, we examined the accuracy of the system by empirically assessing both trueness and precision of measurements using three concrete specimens. Trueness was determined by comparing the surface measurements to those of a highly accurate microscope system, revealing RMSE values of around 40–50 µm. Precision, on the other hand, was assessed considering the scattering of the roughness measurements under repeat conditions, which led to standard deviations of less than 6 µm. Furthermore, to proof validity, a comparative study was conducted based on sixteen concrete specimens, which includes the sand patch method and laser triangulation as established roughness measurement methods in practice. The empirically determined correlation coefficients between all three methods were greater than 0.99, indicating extraordinarily high linear relationships. Among them, the greatest correlation was between the camera-based system and laser triangulation.

Strengthening of plain concrete cylinders with hybrid composites based on basalt and sisal fiber systems

Strengthening and rehabilitation of concrete structures are becoming popular in the construction industry using synthetic fiber reinforced polymers (FRP). However, it has a major drawback due to their economic and environmental impacts. The study focuses on investigation of strength and ductile behavior of concentrically loaded hybrid sisal basalt FRP (HSBFRP) confined concrete structures. A combination of natural sisal and basalt fibers were proposed as the hybrid system. Confined concrete cylinders with different layers of hybrid FRP systems were subjected to various strength tests and test results proved that hybrid FRP confinement intensify the axial load-carrying capacity compared to unconfined specimens. A relative performance analysis of hybrid sisal-basalt FRP confinement with basalt and sisal individual FRP confinements was performed. From the test results it was noticed that the ultimate load carrying capacity increased by 63% along with a fracture energy of 23.17 MPa when the cylinders were confined with 5 layers of hybrid confinement. When compared with unconfined specimens the ductility index attained a maximum value of 4.31 when confined with multiple layers of sisal and basalt FRP wraps. It was proved that with the concept of hybridization in confinement, there was a significant enhancement in fracture energy and ductility index for concrete, thus preventing catastrophic failure.

Performance evaluation of a coating protection system for concrete structures affected by internal expansive reactions

In the last decades, a significant number of large concrete structures with deterioration problems, related to internal expansive chemical reactions, have been detected in Portugal. This type of degradation is associated with the formation of expansive products in concrete causing its disruption, leading to the decrease of the structure’s service life and, ultimately, to the decommissioning or demolition of the structure. In Portugal, structures affected by this pathology are very important in economic and strategic terms, since these reactions are usually encountered in large dams, bridges and viaducts. Two separate material-based mechanisms have been identified to cause the concrete swelling: Alkali-Silica Reaction (ASR) and Delayed Ettringite Formation (DEF). Both reactions result in the formation of expansive products and a common requirement for their occurrence is the presence of a sufficient moisture content inside concrete. By controlling the humidity level in concrete, coatings applied onto the concrete surface should contribute to mitigate ASR or DEF by acting as a barrier against ingress of water and allowing the concrete to dry, as long as they have adequate water permeability characteristics. This paper presents the general criteria that may be followed to select a surface protection system, based on coating materials (hereinafter designated by coating system), for the rehabilitation of concrete structures affected by expansive reactions, in order to mitigate them and, thus, contribute to improve durability and service life of affected structures. In addition, a laboratory study is presented concerning the performance evaluation of a surface protection system, composed of two coating materials, in terms of its capacity to bridge cracks, its permeability to liquid and to water vapour, and on its effectiveness on controlling humidity inside concrete.

Evaluation of interfacial Adhesion between concrete substrate and self-compacting concrete as a repair material

This paper focuses on using self-compacting concrete (SCC) as a material in the repair technique given the advantages it presents in the fresh state, namely: stability, homogeneity, and deformability, because it perfectly matches the shapes of the surfaces to be repaired. The interest is mainly focused on the evaluation of bond strength at the interface: Repair/Substrate. The assessment is made via a repair applied to a half-cylinder of the ordinary concrete substrate (OC), by using as a repair material two classes of self-compacting concrete (SCC) of different strength (30 and 40 MPa), the interface bond strength obtained in this case is compared to that of a half-cylinder (BO) repaired with vibrated concrete (OVC) used as a reference control concrete. The rheological properties of the (SCC) used were determined with the aid of the Slump-flow, L-Box, V funnel, and stability under sieve tests. Mechanical properties include compressive strength, and tensile strength. The test to assess the interface bond strength of the specimens is based on a splitting tensile test (indirect tensile). Finally, to determine the type of failure produced after the test. The results obtained showed that self-compacting concrete appears to be a very promising material in the repair and rehabilitation of concrete structures. SCC offers good interfacial bonding and therefore gives satisfactory interface bond strengths.

Predictive model for slenderness limit of circular RC columns confined with FRP wraps

AbstractApplication of fiber‐reinforced polymer (FRP) for retrofitting and rehabilitation of concrete structures is a common method. The main role of FRP confinement for reinforced concrete (RC) columns is to increase the ultimate strength and strain of confined concrete core and therefore improve in the load carrying capacity of the columns. However, it is possible that a previously short column fails due to buckling after the application of FRP confinement. In other words, the enhanced compressive strength of a retrofitted column may go beyond its buckling load. Therefore, a design criterion to predict this condition is necessary for the designers in the preliminary and final stages of the design. In this paper, a predictive model is proposed to determine the slenderness limit of FRP‐confined circular RC columns. The suggested relation was derived using one of the accurate design‐oriented strength models for FRP‐confined concrete columns as well as analytically derived buckling equations. The effect of hybrid FRP confinement is also incorporated in the suggested slenderness limit. Moreover, a parametric study was performed on the suggested model to specify most influential parameters. The accuracy of the proposed relation was evaluated using a database of experimental results collected from previous studies. The results of the evaluations demonstrated acceptable accuracy of the proposed relation in predicting behavior and failure mode of FRP‐confined RC columns.

Rehabilitation of heavily damaged beam-column connections with CFRP wrapping and SFRM casing

Results of an experimental testing program on two beam-column connections at full scale are presented. Specimens were first tested without initial damage. After that, rehabilitation was conducted using two different techniques, namely: externally bonded carbon fiber reinforced polymer and ultra-high performance mortar reinforced with steel fibers. Specimens were then re-tested. Different loading protocols were used on each specimen to assess their impact on the load-deformation capacity. Such protocols were displacement-controlled and applied quasi-statically. Performance of the specimens, before and after rehabilitation, is presented and discussed in terms of strength and drift capacity, energy dissipation, equivalent viscous damping, effective stiffness, cracking, and visual damage. Interesting findings, useful for the rehabilitation of concrete structures after strong earthquake ground motions, are presented.

Durability of Externally Bonded Fiber-Reinforced Polymer Composites in Concrete Structures: A Critical Review.

Externally bonded fiber-reinforced polymer composites have been in use in civil infrastructure for decades, but their long-term performance is still difficult to predict due to many knowledge gaps in the understanding of degradation mechanisms. This paper summarizes critical durability issues associated with the application of fiber-reinforced polymer (FRP) composites for rehabilitation of concrete structures. A variety of factors that affect the longevity of FRP composites are discussed: installation, quality control, material selection, and environmental conditions. Critical review of design approaches currently used in various international design guidelines is presented to identify potential opportunities for refinement of design guidance with respect to durability. Interdisciplinary approaches that combine materials science and structural engineering are recognized as having potential to develop composites with improved durability.

Behaviour of preloaded concrete cylinders confined by fibre-reinforced polymer composites

The stress–strain behaviour of concrete confined by fibre-reinforced polymer (FRP) is an important part of studying the seismic rehabilitation of concrete structures. Most previous studies have investigated the stress–strain behaviour of concrete prisms confined by polymer composites without preloading, but concrete columns are under various loading conditions before being retrofitted with polymer confinement. Therefore, in this study, FRP-confined concrete cylinders with different preloading ratios were prepared to examine the effect of preloading on the behaviour of retrofitted concrete columns. The results indicated that preloading affects important points of stress–strain curve. Preloading up to 75% of the unconfined concrete strength had a positive effect on the stress–strain behaviour, but 90% preloading reduced the strength of the FRP-confined concrete. A modification for the stress–strain models of preloaded FRP-confined concrete is thus suggested.

Feasibility of textile fabrics for strengthening of concrete column

Renovation and rehabilitation of concrete structures become inevitable when structures reach their service life. Rehabilitation or strengthening of concrete structures using fiber reinforced polymers and textile reinforced mortar are the most common and effective methodologies. However, these rehabilitation techniques are expensive hence cheaper alternatives need to be explored for sustainable concrete structures. Current research program was planned to investigate the efficiency and effectiveness of textile reinforced mortar using locally available textile fabrics on upgrading structural performance of concrete columns. Six locally available fabrics were characterized to select best fabrics for strengthening of concrete columns. Plain Concrete Columns (PCC) were strengthened using epoxy and mortar and selected fabrics with different number of layers. All specimens were tested under uniaxial compression. Results revealed that an increase in axial load carrying capacity ranging between 32% and 58% can be achieved using fabrics along with epoxy. On replacing epoxy with cement mortar, a further increase of up to 23% can be achieved under specific conditions. The use of three layers of textile fabrics might be considered effective as on addition of further layers, the strength gain is not significant. The presented results indicate that the use of textile fabrics may prove to be a promising method of upgrading column’s structural performance.

Modern Techniques for the Restoration and Rehabilitation of Concrete Structures

Civil engineering not only deals with the construction of various structures but also works for their maintenance and rehabilitation. The current era requires efficient and sustainable methods for any job and given that concrete is a material that is heavily relied upon at the present time in construction, therefore its sustainability through the rehabilitation and restoration of buildings is a must and very important. There are many techniques that can be followed in the rehabilitation and restoration of damaged concrete sections, i.e. exposed to cracks, corrosion or disintegration, as each process has its advantages and limitations, which requires the engineer to know the type of damage, the main cause of it and the best way to repair it. Therefore, this paper uses the descriptive methodology to review the latest rehabilitation and restoration techniques used in the treatment of concrete structure including, repointing, grouting, reinforced injection, polymeric materials permitted by fibers and reinforcement of concrete structures, overlays, jacketing, base isolation and stitching. The researcher concluded that these techniques are effective, but each has its determinants of use that must be taken into account before applying them.

Different temperature effects on CFRP wrapped concrete

Carbon Fiber-reinforced polymers (CFRP) wrapping is one of the major methods for repair and rehabilitation of concrete structures. Due to lightweight, high tensile strength and also long-term durability, all this tends CFRP as a major material. In this experimental paper, the different temperatures that are 100 °C, 200 °C, 300 °C, 400 °C are applied and analyze the effects on CFRP wrapped concrete. The experiment is conducted on 150 mm*300 mm size concrete cylinders by wrapping CFRP. CFRP is wrapped on the concrete surface in two methods 1) Exposing concrete to different temperature and wrapped with CFRP(HR)0.2) CFRP is wrapped on the concrete surface then exposed to temperatures (RH). After the analysis of results obtained by experimental studies, CFRP wrapping is gradually increasing the strengths of concrete in 1 & 2 methods, but the deboning of CFRP is observed in both conditions at 4000c. As per experimental results, CFRP wrapping increases the strength of concrete even concrete is exposed to severe temperature conditions up to 300 °C, but strength decreased due to deboning at 400 °C.

Interfacial bond properties between normal strength concrete substrate and ultra-high performance concrete as a repair material

Ultra-high performance concrete (UHPC) is suitable for the durable rehabilitation and strengthening of deteriorated normal strength concrete (NSC) structures due to its excellent characteristics, such as superior compressive strength, high tensile capacity, and extremely low permeability. However, a successful repair depends on whether the UHPC-NSC interface can provide good bonding performance under various applied loads and working conditions throughout its service life. In this study, the bond characteristics between the NSC substrate and UHPC layer were investigated by applying slant shear, splitting tensile, and direct tensile tests, and the interfacial bond strength and corresponding failure modes were observed. Seven studied factors, the roughness of substrate surface, UHPC age, moisture degree of substrate, curing condition of UHPC, strength of NSC substrate, bonding agent and expansive agent were included to explore their influences on the bond strengths, and the UHPC-NSC interfacial bonding enhancement mechanism. Results indicated that the UHPC overlay achieved superior interfacial bond performance for the rehabilitation of concrete structures, with the appropriate surface roughness and substrate wetness. The UHPC-NSC composite samples met the minimum requirements of the interfacial bond strengths specified in ACI 546-06 and achieved an “excellent” bonding quality. Furthermore, the friction coefficient for calculating interfacial bond strength was back-calculated according to the results obtained from the corresponding direct tensile and slant shear tests.

Getting More Out of Existing Structures: Steel Bridge Strengthening via UHPFRC

Ultra High Performance Fiber Reinforced Cement-based Composite (UHPFRC) has been increasingly adopted for rehabilitation projects over the past two decades, proving itself as a reliable, cost efficient and sustainable alternative against conventional methods. High compressive strength, low permeability and high ductility are some of the characteristics that render UHPFRC an excellent material for repairing existing aged infrastructure. UHPFRC is most commonly applied as a surface layer for strengthening and rehabilitation of concrete structures, such as bridge decks or building slabs. However, hitherto its implementation with steel structures has so far been limited. In this work, the UHPFRC strengthening of a steel bridge is investigated both in simulation as well as in the laboratory, by exploiting a real-world case study: the Buna Bridge. This Croatian riveted steel bridge, constructed in 1893, repaired in 1953, and decommissioned since 2010, was removed from its original location and transported to laboratory facilities for testing prior to and after rehabilitation via addition of UHPFRC slab. The testing campaign includes static and dynamic experiments featuring state-of-the-art monitoring systems such as embedded fiber optics, acoustic emission sensors and digital image correlation. The information obtained prior to rehabilitation serves for characterization of the actual condition of the structure and allows the design of the rehabilitation solution. The UHPFRC slab thickness was optimized to deliver optimal fatigue and ultimate capacity improvement at reasonable cost. Once the design was implemented, a second round of experiments was conducted in order to confirm the validity of the solution, with particular attention allocated on the interface between the steel substrate and the UHPFRC overlay, as the connection between both materials may result on a weak contact point. A detailed fatigue analysis, based on updated FEM models prior to and after strengthening, combined with the results of a reliability analysis prove the benefits of adoption of such a solution via the significant extension of the structural lifespan.

Design and testing of an adhesively bonded CFRP strengthening system for steel structures

In the framework of sustainable development policies, it is essential that infrastructure owners can rely on effective repair or strengthening solutions, designed and tested in relevance to actual service conditions. In the case of steel structures, fatigue damage is a major concern that can significantly affect the lifespan of the structure, and so far, there are very few operational methods capable of preventing fatigue cracks in the field. Adhesively bonded carbon fiber reinforced polymer (CFRP) composites are being successfully applied to the rehabilitation of concrete structures for more than two decades, and they are currently receiving much interest for the strengthening of steel elements, but mainly for curative purpose after severe damage has occurred.In the present study, which is part of a European project called FASSTbridge, a specific CFRP system has been developed as a preventive method against fatigue damage of steel structures. The proposed system consists of a commercially available ultra-high modulus (UHM) CFRP composite plate compatible with the stiffness of the host steel structures, which is bonded to the steel support using a novel hybrid epoxy/polyurethane adhesive. A first part of the paper presents the main specifications that should be adopted in the design of CFRP strengthening systems applied to steel structures, and that were identified from an extensive literature survey. These specifications have guided the development of the polymer adhesive and the choice of a peculiar commercial CFRP plate in the preliminary phase of the project. Experimental characterizations were then conducted (i) on the formulated hybrid polymer adhesive to optimize its curing schedule and check the previous specifications are fulfilled, and (ii) on CFRP reinforced steel specimens in order to verify the effectiveness of the proposed strengthening system. This experimental program involved both short term and durability tests that were performed by different laboratories. Such an inter-laboratory study made it possible to verify the performances of the developed strengthening system and to assess the influence of installation parameters and environmental conditions.

Feasibility of Alkali-Activated Slag Paste as Injection Material for Rehabilitation of Concrete Structures

AbstractAlkali-activated materials (AAMs) have recently been used as a suitable replacement for conventional ordinary portland cement (OPC) mixtures. This study evaluates rheological, injectability...

Concrete–fiber-reinforced polymer interfacial bond monitoring with self-triggering sensors

External bonding with fiber-reinforced polymers is currently one of the most popular technologies for rehabilitation of concrete structures. However, the effectiveness of the technology largely depends on the strength of the bond between the fiber-reinforced polymer laminate and the concrete substrate. This article provides a system to monitor the loss of bond between the fiber-reinforced polymer laminate and the concrete. Fiber optic sensors are broadly accepted as a structural health monitoring device for fiber-reinforced polymer materials by integrating the sensors into the host material. A recent development in fiber optic sensor technology is the mechanoluminescence-based optoelectronic sensors. Concrete beams strengthened with multifunctional fiber-reinforced polymer laminates were tested in shear using these sensors to evaluate the bond strength of the composite system. The sensors showed response to shear stress transfer in the adhesive layer which was observed to be as low as 2 MPa. The inclusion of sensors does not affect the bond strength (3.35 MPa), for both beams with sensors and without sensors. Real-time failure detection of fiber-reinforced polymer–strengthened beams was successfully achieved in this study. In future, the scheme aims at providing a tool to reduce the response time and decision making involved in the maintenance of deficient structures.