Article

Rehabilitation of reinforced concrete axially loaded elements with polymer-modified cementicious mortar

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Abstract

The aim of the paper is to investigate the compatibility and the efficiency of the rehabilitation intervention on reinforced concrete columns with polymer-modified cementicious mortar. This paper presents the results of experimental tests on axial behaviour of reinforced concrete columns, with square cross-section, repaired by polymer-modified cementicious mortar. Tests were repeated varying repair thickness, which included or did not include the steel reinforcement on one face of the square column. Despite this type of intervention is quite common in practice, the effect of repair thickness on the intervention efficiency, in relation to the existing steel reinforcement configuration, had not been previously studied in detail for axially loaded elements.Results were discussed and compared with those from control columns, which were tested in non-damaged, non-repaired conditions. The main findings of this work can be summarized as follows. The repair cannot restore the load-bearing capacity of non-damaged control columns, although they give acceptable results. Repairs that include the longitudinal reinforcement show good properties, with stable behaviour, sharing of loads, and plasticization of the material before failure, whereas thin repairs that do not include the reinforcement do not have adequate performance due to premature debonding. Non-linear numerical models also confirmed the different behaviour of the two types of repair.

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... They also worked on reinforced concrete beams in flexure and studied the effect of repairs in both compression and tension zones [5]. Pellegrino et al. [6] investigated the efficiency of rehabilitation interventions on reinforced concrete columns with polymer-modified cementitious mortar. Axially loaded elements were tested by varying repair thickness, which included or did not include reinforcement bars. ...
... Hence, the aim of this study is to give some new insights on the effect of repair mortar properties on the structural behavior of square columns repaired on four sides. Starting from the results obtained by Pellegrino et al. [6], who tested columns repaired on one side only and with one mortar type only, an experimental study on eight axially loaded square columns was carried out. In this study, three polymer-modified cementitious mortars for repair, having different elastic moduli and compressive strengths, were applied over the entire perimeter of six columns. ...
... Column dimensions and repair thickness were selected to compare the test results with those obtained in the previous experimental research [6]. Columns were made with a square section area of 300 Â 300 mm, having 50 mm of repair mortar applied in more than one layer, and a total height of 800 mm. ...
Article
This paper regards the axial behavior of reinforced concrete columns repaired by polymer-modified cementitious mortars. Tests were performed on eight columns with square cross-section: six were repaired with three types of polymer-modified cementitious mortars on all faces, two were in non-damaged and non-repaired condition (control elements). Tests were repeated varying mechanical properties (elastic modulus and compressive strength) of repair materials, maintaining the same repair thickness, including the reinforcement bars. Comparisons between repaired and control elements showed that polymer-modified cementitious mortars cannot restore the original load-bearing capacity of columns. In spite of this, selection of mortar mechanical properties plays a significant role. Among the three types of repair mortar tested in this experimental study, using the material with the most similar elastic modulus and higher compressive strength than that of the concrete substrate is recommended.
... These thicknesses were chosen in accordance with the requirements for sensing [28] and the requirements for non-structural repairs outlined in standard BS EN 1504-3:2005. Structural repair coatings typically require much higher thicknesses (15 mm or 50 mm) [88]. ...
... However, humidity levels were also mentioned to play a role as coatings of equal thickness showcased different behaviors for different exposure to seawater [8]. Thicker cement patches debonded at higher load values than thinner ones under axial loading [88]. ...
Article
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The reinforced concrete structures that support transport, energy and urban networks in developed countries are over half a century old, and are facing widespread deterioration. Geopolymers are an affordable class of materials that have promising applications in concrete structure coating, rehabilitation and sensing, due to their high chloride, sulphate, fire and freeze-thaw resistances and electrolytic conductivity. Work to date has, however, mainly focused on geopolymers that require curing at elevated temperatures, and this limits their ease of use in the field, particularly in cooler climates. Here, we outline a design process for fabricating ambient-cured fly ash geopolymer coatings for concrete substrates. Our technique is distinct from previous work as it requires no additional manufacturing steps or additives, both of which can bear significant costs. Our coatings were tested at varying humidities, and the impacts of mixing and application methods on coating integrity were compared using a combination of calorimetry, x-ray diffraction and image-processing techniques. This work could allow geopolymer coatings to become a more ubiquitous technique for updating ageing concrete infrastructure so that it can meet modern expectations of safety, and shifting requirements due to climate change.
... As this type of repair does not produce the confinement of the column, it is difficult to recover the element's original loadbearing capacity, as was shown in Pellegrino et al. [25]. These researchers studied the behaviour of columns repaired on one side with polymer-modified cementitious mortars, with mechanical characteristics similar to the original concrete. ...
... These were thus ''scaled columns" with a total height of 1360 mm. This way of working is usual in many studies and allows extrapolating the results to real columns, as in Ramírez [30], Colomb et al. [16], Pellegrino et al. [25], Rousakis and Tourtouras [31], and Jain et al. [17]. ...
Article
This paper describes and analyses the results of an experimental programme carried out at the Universitat Politècnica de València on 18 reinforced concrete (RC) columns, 12 of which had been repaired on one side with cement-based mortar before being subjected to axial loading until failure. The objective of the research was to determine the performance of the columns that had been repaired using different mortars, evaluate the influence of Class R3 and R4 mortar used and of the application of a binder or bonding agent. The results obtained were compared with those of the undamaged control columns and those of the unrepaired damaged columns to obtain values for the efficiency of the repairs and for the improvement in the load-bearing capacity of the columns. The results obtained indicate that the columns repaired with Class R3 mortar, with a lower elasticity modulus, function in better way than the Class R4 repaired ones. The presence or absence of a binder was not found to be a determining factor in improving the behaviour of the repaired elements. The chief novelty of the study lies in the fact that it is the first experimental study on RC columns totally repaired on one side only, using different types of mortar with and without the application of a binder.
... Beams designed to fail in flexure could re-establish original beam capacity with both types of repair thickness. In this framework, the effect of the geometric configuration of the repair material (position and thickness) on the efficiency of the rehabilitation inter- vention [17] , in relation to the existing steel reinforcement configuration (both in tension and in compression regions), was not comprehensively studied for flexural elements but only some aspects have been analysed separately. In this work an experimental investigation to control the effectiveness of polymer-modified cementicious mortar repairs applied to beams under flexural loads is carried out. ...
Article
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This paper presents the results of experimental tests on flexural behaviour of reinforced concrete beams repaired by polymer-modified mortar. Tests were repeated varying repair thickness, which included or did not include the steel reinforcement. Also the position of repair mortar was varied, as it was carried out either in the tension or compression region. Finally, the reinforcement ratios of beam sections were also varied. Results were compared with those from control beams, which were tested in non-damaged, non-repaired conditions. Thick repairs that include the longitudinal reinforcement can restore the load-bearing capacity and ductility of non-damaged control beams, whether they are applied in the tension or in the compression region. Thin repairs in tension, which substitute the concrete cover, but do not include the reinforcement, can even decrease the load bearing capacity and ductility of the beam, whereas thin repairs in compression are more effective than those in tension. KeywordsReinforced concrete–Repair mortars–Interface–Cracking
... The case can be solved in double symmetry and 2D plane strain (Fig. 5). If a different material is used to repair a damaged concrete structure (Pellegrino et al. 2009) it is important to take this into account in the numerical simulation. Using Cast3M it is possible to join different materials and also to assign different mechanical properties to the interface, to take into account the treatment of the surface on which the repair will be applied. ...
Article
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Experience has shown that repairs of concrete structures are often subject to premature cracking because the already dry and rigid substrate of the damaged structure contrasts the drying and self-drying contractions of the new material of restoration. In this paper a thermo-hygro-chemo-mechanical (THCM) model for concrete at early age is presented and used to analyze the behaviour of a real repair case taking into account casting and environmental conditions. The multi-physics mathematical model is a simplified version of COMES-HTC (developed a few years ago by Gawin, Pesavento & Schrefler, 2006). The THCM model for concrete at early age has been implemented in the French finite elements code CAST3M (developed by the CEA, Commissariat à l'Energie Atomique Français).
... The case can be solved in double symmetry and 2D plane strain (Fig. 5). If a different material is used to repair a damaged concrete structure (Pellegrino et al. 2009) it is important to take this into account in the numerical simulation. Using Cast3M it is possible to join different materials and also to assign different mechanical properties to the interface, to take into account the treatment of the surface on which the repair will be applied. ...
... If a different material is used to repair a damaged concrete structure (as often happens in real applications [13]) it is important to take this into account in the numerical simulation. With Cast3M it is possible to join different materials and also assign different mechanical properties to the interface, to take into account the treatment of the surface on which the repair will be applied. ...
Conference Paper
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In the field of civil engineering strengthening and repair of concrete structures are becoming more studied. Experience has shown that concrete structures repairs are often subject to premature cracking because the substrate prevents the free contraction of the new material of restoration. Indeed, as it is known, cement paste at early ages is subject to various physical and chemical phenomena which determine thermal, hygrometric, chemical and viscous strains. In order to quantify with a mechanistic approach these deformations, a THCM multi-phase model of hygrothermal and hydration phenomena in concrete at early ages has been developed by B.A.Schrefler, F.Pesavento and D.Gawin. The introduction of this numerical model in the French finite elements code Cast3M allows its opening to a wide range of applications including the study of repair problems, realized either with ordinary concrete, or with shrinkage-compensated or fiber-reinforced concretes. The paper will explain the multi-physics formulation of the numerical model and will introduce some application examples.
... Despite the fact that a number of experimental investigations on strengthening of RC elements by means of FRP are easily available in the literature, very little information is available about cementitious composite reinforcement. Some examples of studies on composites with cementitious matrix can be found in [21][22][23][24][25][26][27][28][29][30][31][32][33][34], whereas recent experimental applications of cement-based composites for rehabilitating existing structural elements developed at the University of Padova can be found in [35][36][37]. ...
Article
Strengthening of reinforced concrete (RC) members by means of fibre reinforced polymers (FRP) has gained increasing importance in the last few decades. On the other hand the necessity of skilled labour, high costs and particularly the weak response under high temperature conditions represent critical issues for the effective application of this technique. The use of fibre reinforced cementitious matrix (FRCM) composites applied to RC members seems to be a promising technique since it combines cost economy and high performance. Despite the fact that a number of experimental investigations on strengthening of RC elements by means of fibre reinforced polymers (FRP) composites are available in the literature, very little information is available about fibre reinforced cementitious matrix composite (FRCM). Hence, the use of cementitious composites in strengthening of RC structures is strongly limited by the lack of design models, guidelines, and recommendations and by the few available experimental investigations. This work aims to better understand the behaviour of FRCM strengthened RC full-scale elements through experimental tests on precast prestressed double-T beams. In addition to investigating the experimental behaviour of an innovative and promising strengthening system, a further element of novelty of the work is that the tested beams belong to an actual existing industrial building, since the few experimental tests available in the literature are mostly related to small-scale and cast-in-place RC elements.
... On the other hand, the rehabilitated specimen, PCC-2-R successfully attained 94.68% of the ultimate load as attained by PCC-2, which is comparable to the results obtained by Pellegrino et al. (2009) while rehabilitating reinforced concrete axially loaded elements with polymer-modified cementitious mortar. Though the initial stiffness was same as that of the controlled one, the onset of stiffness degradation occurred at lower load of about 35 kN. ...
Thesis
Geopolymer is an emerging material that has strong potential for replacing Portland cement in concrete. Geopolymer binder uses by-product materials such as flyash, blast furnace slag and silica fume. Thus its use can reduce CO2 emission, minimizing the environmental impact caused by the construction industry. Review of literature reveals that data on mechanical, durability and rheological properties of geopolymer concrete are abundant. However, investigation on such concrete with reinforcement is limited. In the present study, an attempt has been made to investigate the behaviour of reinforced geopolymer concrete due to cyclic flexural load. Tests were also performed to investigate the behaviour of plain geopolymer concrete due to static compressive, tensile and flexural load. For the comparison of the results, similar type of tests were performed on some other types of concrete such Portland cement concrete, polymer Portland cement concrete, latex modified concrete and latex modified geopolymer concrete. Further, feasibility of geopolymer as rehabilitation material was investigated. Controlled specimen was tested under static and dynamic loads. The damaged specimens were then rehabilitated with geopolymer paste and geopolymer mortar and test again under tests similar to that of the controlled specimen. It was observed that geopolymer concrete and latex modified geopolymer concrete exhibit better strength than Portland cement concrete and latex modified concrete when tested under static load. The stiffness and energy dissipation capacity of geopolymer concrete and latex modified geopolymer concrete when tested under dynamic load were also better than Portland cement concrete and latex modified concrete. Polymer Portland cement concrete exhibited similar static strength characteristics as that of geopolymer concrete and latex modified geopolymer concrete. However, the stiffness degradation was greater and energy dissipation capacity was lower than geopolymer concrete and latex modified geopolymer concrete. Properties of latex modified concrete were observed to be inferior among all types of concrete used in the present study. Latex modified geopolymer concrete exhibited superior behaviour to geopolymer concrete under static and dynamic loads. Geopolymer also performed satisfactorily as rehabilitation material. Geopolymer rehabilitated specimens subjected to static and cyclic flexural loading were able to attain approximately 90% of their original strength.
... Furthermore, experimental investigations on real-scale flexural elements are very few [4]. Some examples of studies on composites with cementitious matrix can be found in [5][6][7][8][9], whereas recent experimental applications of mortars for rehabilitating existing structural elements developed at the University of Padova can be found in [10,11]. This paper describes the experimental investigation on four precast pre-stressed TT beams taken from an existing industrial building where they were used as roof elements. ...
Article
A number of experimental investigations on fibre reinforced polymer (FRP), with the aim of understanding their behaviour when applied as strengthening of reinforced concrete elements, are available in the literature but very few information is available on strengthening real-scale elements with cementitious composites. In particular design code formulations are scanty or non-existent. In this study the behaviour of four precast pre-stressed TT beams taken from an existing industrial building was investigated. One of them was considered as control unstrengthened TT beam, whereas the others were strengthened with different techniques, namely with FRP laminates (glued with epoxy resin), carbon fibres with cementitious matrix and steel fibres with cementitious matrix. Each material involved in this study was also mechanically characterized to obtain the main physical properties. Adequate specimens were obtained from the existing TT beam to characterize the concrete and the reinforcing steel bars.
... From the researches in recent years, styrene-butadiene rubber (SBR) latex has excellent mechanical properties, flow ability, and impermeability to make better modification on the cement mortar and cement concrete [1][2][3]. The flexural strength, working performance, and durability of the concrete modified by the polymer have greatly improved except resistance to sulfuric acid [4][5][6]. The fiber can also improve the resistance of the concrete cracking. ...
Article
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Polyester fiber and SBR latex cement concrete is prepared as pavement surface material; its fracture properties including fracture toughness, fracture energy, CMOD, and flexural strength are studied comparing with those of normal concrete (NC), polyester fiber modified concrete (FMC), SBR polymer modified concrete (SMC), and the combination of polyester fiber and SBR polymer modified concrete (FSMC). The modification mechanism of the latex and fiber on the concrete was also studied by the methods including X-ray test, chemically combined water, heat of hydration, water loss, and scanning electron microscope. Results indicated that the concrete modified by latex and polyester fiber has flexural strength, fracture toughness, and fracture energy of 44.4%, 397.0%, and 462.8% higher than the reference normal concrete, the polymer retarded the hydration process and reduced the hydration degree of cement at early age, while the hydration degree is promoted by the polymer film for its excellent water resistance after 28 d, and the bond between the fiber and cement paste is improved by the latex.
... Respecto a las investigaciones realizadas en el campo de la reparación de pilares de hormigón armado, se pueden destacar las realizadas por Shambira y Nouno [8], la de Sharif et al. [9] y la de Aurrekoetchea [10] referidas a las reparación por parcheo. En cuanto a la reparación integral a una cara, podemos citar la de Pellegrino et al. [11] y [12], que cuantifica la efectividad de la reparación en función del espesor de la misma. Y finalmente, cabe citar la de Da Porto et al. [13], relativa al restablecimiento de la capacidad de carga en los pilares reparados a 4 caras. ...
Conference Paper
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Nowadays, there is an important number of buildings with structural problems in Spain. Among the reinforced concrete elements of a building, damages in columns are the most frequent and critical, due to their importance in the safety of the whole building. These problems are very common in buildings over 30 years old. Even though there are European regulations to indicate how to repair these damages, it is very frequent to repair them without any durability guarantee. Especially in small buildings, the repair consists in the use of commercial products without previous studies to determine the causes and the importance of the damages of the whole structure. Nevertheless, it is necessary to perform a set of previous studies before repairing the damaged elements. From these studies it is possible to understand the causes of the damage and to assess the strength of the structure, to determine which repair or strengthening method to use. In this paper, a methodology applied to damaged RC columns in a basement of a building is presented.
... The problems associated with the cement grouts have led to the technique of adding various cementitious materials in single or blended/ multi blended with cement to improve the various properties and performance of concrete, mortar and grout [10][11][12][13][14][15][16]. Recently, a substantial application of various types of polymers as a binder has been made in the production of concrete and mortar which is also gaining acceptance in the production of gouts. ...
Article
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Grouts are very commonly used in repairing the cracks which are developed in the structural elements. Normally, the grouts are prepared with a combination of the cement as binder and the fine sand as filler. This paper presents the results of an experimental investigation carried out to investigate the effectiveness of using the marble powder as filler over the compressive strength of the cement and polymer grouts. The marble powder is a waste product which can easily be obtained during the cutting process of the marble pieces. In addition, the sand and a mixture of the sand and marble powder have also been used as fillers for comparison of the results. Three proportions of the marble powder in terms of binder to filler ratios of 1:1, 1:1.5, and 1:2 by weight have been used. The test results have revealed that the resin grouts exhibit manifold compressive strength when compared to that of the cement grouts. The increases in the compressive strength of the resin grouts were remarkable when the marble powder only was used as filler and were the highest when the marble powder was used with an equal proportion of the sand.
... The study consisted of tests on eighteen 1370 mm long specimens to simulate axially loaded RC columns. Although these dimensions are not those of normal columns, the results can be extrapolated to real columns, as has been previously shown: Emberson and Mays [26,27], Ramírez [5], Mourad and Shannag [10], Pellegrino et al. [36], Achillopoulou and Karabinis [37], Fukuyama et al. [20] and Dubey and Kumar [8]. ...
Article
Full-text available
This paper describes a study carried out in the ICITECH laboratories (Universitat Politècnica de València) on RC columns repaired on all four sides with cementitious-based mortars. A total of 18 specimens were tested, representing a group of square 20x20 mm2 columns subjected to compressive axial loads. Different repair scenarios were considered in order to study the influence of the type of mortar used and the presence or absence of bonding agents between the mortar and the column concrete. The results obtained showed that bonding agents have no appreciable effect on the behaviour of the repaired columns. Of the two types of mortar used in the study (Classes R3 and R4), the columns repaired with the lower grade mortar (R3) were seen to behave better. The main novelty of this work lies in the fact that this is the first time that two types of mortar are compared in the repair of four column sides, in addition to the possible use of bonding agents between the mortar and the column.
... Furthermore, experimental investigations on real-scale flexural elements are very few [4]. Some examples of studies on composites with cementitious matrix can be found in [5][6][7][8][9], whereas recent experimental applications of mortars for rehabilitating existing structural elements developed at the University of Padova can be found in [10,11]. This paper describes the experimental investigation on four precast pre-stressed TT beams taken from an existing industrial building where they were used as roof elements. ...
Article
A number of experimental investigations on fibre reinforced polymer (FRP), with the aim of understanding their behaviour when applied as strengthening of reinforced concrete elements, are available in the literature but very few information is available on strengthening real-scale elements with cementitious composites. In particular design code formulations are scanty or non-existent.In this study the behaviour of four precast pre-stressed TT beams taken from an existing industrial building was investigated. One of them was considered as control unstrengthened TT beam, whereas the others were strengthened with different techniques, namely with FRP laminates (glued with epoxy resin), carbon fibres with cementitious matrix and steel fibres with cementitious matrix. Each material involved in this study was also mechanically characterized to obtain the main physical properties. Adequate specimens were obtained from the existing TT beam to characterize the concrete and the reinforcing steel bars.
... The technique consists of restoring the concrete manually, as indicated in Principle 3 of the EN 1504-9:2008 [1]. The repairs are thus restricted strictly to the damaged area and so are less costly than other techniques such as repairs to one side only [2] or to all four sides [3]. ...
Article
This paper describes an experimental study on patch-repaired reinforced concrete columns subjected to axial loads until failure. The behaviour of four series of columns repaired with Class R3 and R4 cement-based mortar was analysed both with and without a bonding agent. The results obtained were compared with control series of undamaged and damaged but unrepaired columns to determine the effectiveness of the repairs and the subsequent improvement in the behaviour of the columns. The results of this study were compared with those of previous work by the authors on the analysis of all-four-side repairs and one-side repairs. The conclusion reached was that patch repairs are highly effective as compared to the other techniques studied and that using Class R3 mortar achieves better results on damaged columns made with low-quality concrete. It was also concluded that applying a bonding agent does not improve the results, although this element was found to be necessary to prevent the premature detachment of the repair when there is a substantial difference between the stiffness of the column concrete and that of the mortar used in the repairs.
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Despite the fact that polymer-modified mortar can be widely used as a material for major construction projects, the extensive use of this promising material may be hampered because of not enough published data on its durability performance. This paper, based on a laboratory program, compares the engineering properties, over different aging, of three commercial polymer-modified mortars [styrene-butadiene rubber (SBR), polyacrylic ester (PAE), and vinyl acetate-ethylene (VAE)] and unmodified conventional mortar mixes exposed to different curing conditions. The results show that the SBR mixes appeared to possess better engineering properties than the PAE and VAE mixes, and a well-designed polymer-modified mortar mix can retain its engineering properties over a long period of time.
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The main purpose of this study was to investigate the distribution of potential of steel in patching-repaired concrete. Reinforced concrete specimens were prepared with and without patching repair, made with various concrete mix proportions. Experimental results revealed that patching repair showed good effectiveness for restoring corroded reinforced concrete structures. The highest half-cell potential of steel was observed in a repaired area (patch), surrounded by a lower potential of steel in a non-repaired area (substrate). A comparison between individual concrete and patching-repaired concrete revealed that there was a redistribution of the potential along with the steel in patching-repaired concrete. The variation of the potential depended on the parameters of concrete, which include the water to binder ratio, fly ash content, and chloride content. Finally, a numerical model to simulate the electrochemical corrosion of steel showed good agreement with the measured potential.
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The cementitious fireproof material is widely used to protect concrete structures against fire. However, there has lately been interest in developing more environmentally friendly construction materials that have lower cement content, since cement manufacture has a large carbon footprint. One approach, formulated here, makes use of eco-friendly fireproof high-strength polymer cementitious composites made from blast furnace slag (an industrial by-product). And we were used the activator which is necessary to function as a catalyst to induce the hydration of blast furnace slag. In addition, we were used the polypropylene fibre, and porcelain to improve the fire-resistance. To evaluate the properties of eco-friendly fireproof high-strength polymer cementitious composites, we tested mechanical properties in laboratory experiments such as compressive strength and fire-resistance. The tested composite performed just as well as conventional fireproof cement material, and notably had high residual strength.
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Cement-based materials, such as concrete and mortars, are used in extremely large amounts. For instance, in 2009 concrete production was superior to 10 billion tons. Cement plays an important role in terms of economic and social relevance since it is fundamental to build and improve infrastructure. On the other hand, this industry is also a heavy polluter. Cement production releases 5–6% of all carbon dioxide generated by human activities, accounting for about 4% of global warming. It can release huge amounts of persistent organic pollutants, such as dioxins and heavy metals and particles. Energy consumption is also considerable. Cement production use approximately 0.6% of all energy produced in the United States. On the other hand, the chemistry underlying cement production and its applications can be very helpful to overcome these environmental issues. In terms of manufacture, there are many alternative materials that can be used to minimize carbon dioxide production and reduce energy consumption, such as calcium sulfoaluminates and β-Ca2SiO4—rich cements. Using residues from other industrial sectors can also improve the sustainability of cement industry. Under adequate conditions, waste materials such as tyres, oils, municipal solid waste and solvents can be used as supplementary fuel in cement plants. Concrete can be used for encapsulation of waste materials such as tyres, plastics and glasses. In this review, we discuss some aspects of the cement industry associated with environmental science. Other issues such as economic aspects, the chemistry of cement manufacture and its properties are also presented. Special attention is given to the role that cement chemistry can play in terms of sustainability. The most relevant aspects are outlined, such as the use of alternative materials, new possibilities and also the recycling of materials. It is also argued that an important aspect is the role of research and development necessary to improve cement sustainability.
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The patch repair method is one of the most common approaches used by engineers for repairing reinforced concrete structures that have been damaged. Despite its popularity, the knowledge on material properties pertinent to a durable structural repair is still lacking. Most standards and guidelines on concrete repair currently specify arbitrary limits when it comes to the properties of repair materials. In the case of structural patch repairs, these arbitrary limits have led to the development of high-strength cementitious repair mortars, often marketed as “high-performance”, that are tailored to meet the specifications and not the needs on-site. The paper discussed here forms part of a greater study that aims to increase the understanding of patch repairs and inform existing guidelines on designing structural patch repairs. Three commercially available high strength cement-based repair materials were tested for their strength, elastic modulus, shrinkage, and creep properties. These properties were then used as inputs to an analytical model that was developed to determine the distribution of stress in a repaired element over-time. The results from the analytical model suggest that high strength materials do not structurally contribute in the long term, for patch repaired concrete elements under axial compression.
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The paper aims to contribute to a better understanding and modeling of the shear behavior of reinforced-concrete (RC) beams strengthened with carbon fiber reinforced polyiner (FRP) sheets. The study is based on an experimental program carried out on I I beams with and without transverse steel reinforcement, and with different amounts of FRP shear strengthening. The test results provide some new insights into the complex failure mechanisms that characterize the ultimate shear capacity of RC members with transverse steel reinforcement and FRP sheets. After the discussion of the above topics, a new upper bound of the shear strength is introduced. It should be capable of taking into account how the cracking pattern in the web failing under shear is modified by the presence of FRP sheets, and how such a modified cracking pattern actually modifies the anchorage conditions of the sheets and their effective contribution to the ultimate shear strength of the beams.
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Bond behaviour between externally bonded Fiber Reinforced Polymer (FRP) strengthening and concrete supports is essential in shear and flexural applications, in order to transfer stress between concrete and external reinforcement, and influences the nominal capacity of the structural element. In the majority of cases, constitutive models tau-s (shear/bond stress-slip) available in the literature, are not directly calibrated with experimental results, partly due to the difficulty of obtaining tau-s diagrams experimentally. This paper aims at improving knowledge of bond behaviour between FRP and concrete, and presents a critical review of the principal bond-slip models currently available in the literature and a new proposal calibrated on the basis of experimental tau-s diagrams, taking into account the influence of FRP strengthening rigidity. A new expression for interfacial fracture energy is also proposed and validated with experimental results.
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This paper reviews works on repairing of deteriorated reinforced concrete beams. Every structural element should be designed for a particular type of loading as well as for adopting of different types of environment. However many civil structural elements, like reinforced concrete beams are often required to be repaired to restore the structural integrity and to protect the reinforcement from sever weathering condition. Recently repairing is gradually increasing with the increase of age of concrete structures. In some instances it may be more economical to accept the need for maintenance or repair at suitable intervals than to attempt to build a structure that will be maintenance-free under severe conditions for a long period. Several types of materials and techniques are available for repairing of exiting deteriorated reinforced concrete beams. In this paper, causes of deterioration of concrete as well as repairing by using cement grout, mortar, concrete, sprayed concrete or shotcrete, epoxy, ferrocement with mortar, Fiber Reinforced Polymer (FRP) Sprayed Fiber Reinforced Polymer (SFRP) and the techniques of applying of these materials and also some resin based materials for bonding agent between interface of old concrete and newconcrete are reported.The advantages anddisadvantages ofthesematerials,causes ofdebondingbetweenconcretesubstrateandnewconcreteapplied on substrate and preventive measures are also discussed.
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Non-destructive (ND) evaluation by thermographic analysis was applied to reinforced concrete (RC) beams strengthened with CFRP laminates, to assess the quality of the interface between reinforcement and substrate before and under loading, during laboratory bending tests. The proper algorithm for processing data acquired from the thermographic system was first selected by testing reduced-scale fiber reinforced polymer (FRP)-strengthened concrete slabs with artificial defects and anomalies, deliberately placed at the interface. Portable heating equipment was purposely set-up to allow continuous scanning along the loaded beams. Results showed that infrared thermography (IRT) can supply significant qualitative and quantitative information on bonding of FRP materials applied to structural substrates, for both preliminary and in-situ investigations, by means of a reliable low-time-consuming procedure. Cross-evaluation of crack patterns during bending tests and thermographic results are also presented.
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This paper deals with the shear strengthening of Reinforced Concrete (RC) flexural members with externally bonded Fiber-Reinforced Polymers (FRPs). The interaction between an external FRP and an internal transverse steel reinforcement is not considered in actual code recommendations, but it strongly influences the efficiency of the shear strengthening rehabilitation technique and, as a consequence, the computation of interacting contributions to the nominal shear strength of beams. This circumstance is also discussed on the basis of the results of an experimental investigation of rectangular RC beams strengthened in shear with “U-jacketed” carbon FRP sheets. Based on experimental results of the present and other investigations, a new analytical model for describing the shear capacity of RC beams strengthened according to the most common schemes (side-bonded and “U-jacketed”), taking into account the interaction between steel and FRP shear strength contributions, is proposed.
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The repair and rehabilitation of concrete structures has increased worldwide in recent years. However, the service life of concrete repair depends on the correct choice and proper use of repair materials. Mistakes in design, selection of materials, and construction practices will lead to incompatibility between the repair and the existing concrete substrate. Most of the literature reported in the field of repair reveals that dimensional incompatibility, drying shrinkage in particular, is one of the major problems of concrete repair. This paper addresses the problem of stress buildup in concrete repair in the form of a jacketed column resulting from moisture diffusion. As moisture evaporates from the external jacket into the surrounding ambience of known relative humidity, the hardened concrete column restrains free-shrinkage movement of the repair layer. As a consequence, primary tensile stresses are set up in the jacket due to restrained shrinkage. The jacketed layer under increasing tensile stresses is also subjected to tensile creep deformation, which results in a stress field of reversed sense as that due to restrained shrinkage. These secondary stresses due to restrained creep serve to relieve the primary shrinkage-associated stress field, and, as a result, the net or total stress buildup is reduced. A nonlinear finite element model is used to obtain the time-dependent moisture loss profile in the jacketed column. This model is interfaced with a finite element-based two-dimensional stress analysis program called SHCPAN for computing time-dependent restrained shrinkage and creep stresses. For a typical column repair, numerical experiments are carried out to highlight the influence of both a sealed jacket/column interface and a porous interface on the stress buildup in the jacketed columns.
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Approximately £500m is spent in the UK each year on the repair of concrete members. In recent years researchers have been paying increasing attention to the structural implications of property mismatch between patch repair materials and the substrate reinforced concrete. Parts 1 and 2 of this study, published in 1990, discussed the measurement of relevant mechanical and physical properties of repair systems and applied these results to the study of axial load transfer through simple patch repairs. This paper extends the approach to reinforced concrete beams repaired in either the flexural compression or tension zones and subjected to short-term static, long-term creep and cyclic loading. The research has shown that the performance of patch repaired reinforced concrete beams can be predicted from a knowledge of the basic physical and mechanical properties of the repair material and the substrate concrete. Given suitable repair materials and mode of application, satisfactory structural performance may be achieved in both the short and the long term.
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Approximately £500 m is spent in the UK each year on the repair of concrete members. Despite the existence of this large and expanding market, little fundamental attention has been paid to the structural implications of property mismatch between patch repair materials and the substrate reinforced concrete. Part 1 of this Paper has discussed the measurement of mechanical and physical properties of repair systems considered relevant to the subsequent structural performance of a repaired member. Using the range of material properties determined for nine generically different systems, two- and three-dimensional linear elastic finite element techniques have been used to elucidate axial load transfer through simple patch repairs in reinforced concrete members. Areas of localized concentrated stress and requirements for especially high values of adhesion become apparent when the modulus of the repair material differs significantly from that of the concrete substrate. Comparison of the finite element results with...
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Experimental investigation is conducted to assess structurally the effectiveness of patch repair in axially loaded columns. Two patch repair materials are selected with high and low modulus of elasticity. The concrete columns were patch repaired under loaded and unloaded conditions. The patch repair is structurally effective for concrete columns repaired in an unloaded state. While for concrete columns repaired in a loaded state, the patch repair is structurally effective only when additional loading is applied. The load distribution between the patch repair, concrete core and steel reinforcement depends on the modulus of elasticity and areas of these components in the composite section at the repaired zone. For patch repair to be structurally effective, it is recommended to relieve the loads before the patch repair is applied either partially or totally if constructionally possible.
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Jacketing method with reinforced concrete (RC), steel plates or carbon fiber (CF) sheets has been widely used to repair or strengthen the RC columns damaged by the 1995 Hyogoken-Nanbu earthquake. The purpose of experimental studies reported in this paper is to confirm those repair or strengthening effects. To investigate the shear strength and ductility of RC columns repaired or strengthened by jacketing, eight column specimens were tested under constant axial compressive load and cyclic shear forces. The main conclusions obtained from the test were summarized as follows. (1) Shear strength and ductility of the repaired columns, in which the concrete remained crushed and the longitudinal bars remained buckled, can be restored over the pre-damaged level. (2) The maximum shear strength of the column repaired or strengthened by jacketing with RC, steel plates or CF sheets can be calculated by the formulas proposed in this paper.
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Results are presented from experimental work that was conducted in order to study the! mechanical behavior of damaged structural elements in bending. Both repaired and unrepaired concrete elements (beams) were considered in this program. These elements were damaged using an accelerated local corrosion process that consisted of chloride penetration. Both locally corroded tensile reinforcement (Series 1) and locally corroded compressive reinforcement (Series 11) are considered independently. The Structural behavior and the efficiency of repair systems in the ultimate and service limit states were evaluated. The work focuses on the pattern of structural cracks, displacements, load-bearing capacity, and ductility variations to examine the influence of the adopted repair systems on both limit states. The experimental results made it possible to assess the effect of the detailing, the degree of corrosion, and the presence of the repair patch in the structural behavior of the beams. As a result, general recommendations are proposed for patch-repaired elements.
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Approximately £500 m is spent in the UK each year on the repair of concrete members. Despite the existence of this large and expanding market, little fundamental attention has been paid to the structural implications of property mismatch between patch repair materials and the substrate reinforced concrete. To pursue this question, it was necessary to identify the desirable characteristics of repair systems for satisfactory structural performance, and then to measure the relevant mechanical and physical properties of the various systems currently on the market. It was found that these repair systems could be conveniently categorized in nine generic types; a representative system from each was selected. Properties measured included strength, modulus, Poisson's ratio, coefficient of thermal expansion, tensile adhesion, early curing shrinkage, long-term creep and shrinkage. Where deemed appropriate, standard test methods have been utilized; otherwise techniques have been developed specifically for the purpose. These techniques, some of which now form the drafts of revisions to British Standards, are described. The range of property values determined are discussed in relation to patch repairs in typical reinforced concrete members and the desirable characteristics previously identified.
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This paper reports the results of an experimental study of the effect of time-dependent deformations (such as shrinkage and creep) of concrete repair materials on the ability of patch repairs to contribute to the structural function of reinforced concrete short columns. Prior to repair, strain measurements were taken from loaded columns with preformed cavities; cavity depths varied between columns. One polymeric and one polymer-modified concrete repair material were used for repair, all repairs being performed under zero load. After repair, the distribution of strain was measured from columns subjected to axial service load and from similar columns observed under zero load. Test results indicate that in the short term both the repair materials assist the repaired column to carry load, but in the long term the contribution of the polymer-modified material is reduced substantially while that of the polymeric material is sustained. It is observed that shrinkage of the repair material can induce bending in the repaired column and that this bending increases with patch repair cavity depth. Within the repaired zone, bending strain distributions were linear which would suggest that conventional methods of structural analysis are appropriate for such members.
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Strengthening, maintenance and repair of concrete structures are becoming more recognised in the field of civil engineering. There is a wide range of repair mortars with varying properties, available in the market and promoted by the suppliers, which makes the selection of the most suitable one often difficult. A research programme was conducted at Leeds University to investigate the properties of cementitious, polymer and polymer modified (PMC) repair mortars. Following an earlier publication on the intrinsic properties of the materials, this paper presents results on the compatibility of these materials with concrete. The dimensional stability is used in this study to investigate the compatibility of the repair mortars and the parent concrete. Composite cylindrical specimens (half repair mortar/half concrete) were prepared and used for the measurements of modulus of elasticity and shrinkage. The results of the different combined systems were obtained and compared to those calculated using a composite model. The variations between the measured and calculated values were less than 10%. The paper attempts to quantify the effect of indirect differential shrinkage on the permeability and diffusion characteristics of the different combined systems.
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This paper presents the results of an experimental investigation on a total of 30 under-reinforced concrete beams which were subjected to corrosion after the cover zone was replaced with different high-performance fiber reinforced cementitious composites. A power supply was used to induce different degrees of corrosion into reinforcement. The beams were then tested under four-point bending for their load–deflection relations. The results show significant reductions in flexural strength due to reinforcement corrosion. The beams cast with a cover containing 50/50 blend of brass coated and hooked steel fibers have the best flexural performance. The beams cast with a cover containing glass fiber showed the smallest amount of strength reduction and a reasonable ductile failure after corrosion.
Article
Many shear dominant structural members in existing concrete structures have been evaluated as below serviceable standard requiring strengthening and/or repair. In order to repair these aged reinforced concrete (RC) structures, a section replacement method of removal and replacement of old concrete and/or steel reinforcements of damaged sections with new concrete and/or steel reinforcements are commonly used. However, this repairing method is used without understanding the complicated structural behavior such as shear behavior of RC structures. Also, the materials commonly used for repairing are concrete and cement mortar. In order to implement the material superiority of newly developed cement based material and to complement the disadvantages of cement-based construction materials such as brittleness of failure, Ductile Fiber Reinforced Cementitious Composite (DFRCC), a high performance cementitious composite with superior strain capacity, is currently being used as a repair material. However, the composite behavior between old substrate and new repair material is not clearly understood at present. In order to effectively apply DFRCC as repairing material on RC structure, the interface, the weakest part in the repaired system where most failures occur, must be studied in depth. In this research, the composite behavior of a RC flexural member repaired using the superior tensile capacity of DFRCC on the tensile face of a RC specimen is studied. Two types of DFRCC repaired RC specimens are tested, one is without shear stirrups and the other is with shear stirrups. By comparing these two types of DFRCC repaired specimens, the failure mechanism and interface debonding behavior as well as repairing capacity can be effectively studied.
Article
There is an urgent need to develop efficient methods for the repairs and rehabilitation of currently existing structures, they are being deteriorated over time, and also the magnitude of loadings keeps rapidly increasing for such structures. Possibly one of the most challenging tasks in the rehabilitation processes is to upgrade the overall capacity of deteriorated concrete structures. Recently, considerable efforts are being directed toward developing new construction materials. This paper presents the experimental study for the flexural behavior of reinforced concrete beams repaired by Polymer Cement Mortar (PCM) and Ordinary Portland Cement Mortar (OPCM) in the tension region. Tests were performed for eight reinforced concrete beams with varying reinforcement ratios, repair materials and repair lengths. Emphasis is given to overall bending capacity, deflection, ductility index, failure mode and crack development of repaired beams. The results are compared with those from the control beam.
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The objective of this paper is to compare the characteristics and effectiveness of ten reinforced concrete column repair methods. The repair is performed in order to counterbalance a significant or total loss of carrying capacity. The methods presented are divided into two groups. The first deals with the strengthening of the entire column height, while the second focuses on the problem of damage and loss of strength on a localized section. They use different kinds of standard and polymeric concrete jackets, steel profiles and bonded, welded or bolted plate jackets and encasements. The paper concludes identifying the advantages and limitations of the various strengthening methods.
Article
The effectiveness of reinforced concrete repairs may be established in terms of their ability to restore the structural integrity of the reinforced concrete element and to protect the reinforcement from severe weathering conditions. Therefore, 18 large scale reinforced concrete beams were cast and subject to an accelerated corrosion mechanism in a chloride environment. The beams were repaired using two different materials for comparison purposes, namely an OPC mortar and a free flowing micro-concrete. Twelve beams were tested just after the repair material has cured, and the remaining beams were subjected to an aggressive weathering cycle for 6 months after which structural and electrochemical testing were conducted. This paper presents the results of both structural load testing of all beams, and physical and electrochemical performance of repaired beams before and during the accelerated weathering. The results of structural testing showed that in short-term situation both materials behaved very similar to each other and were able to restore 60–70% of the beams’ capacity. But in long-term situation the OPC mortar beams has deteriorated badly showing extensive cracking, while the free flowing micro concrete beams have shown very little cracking. The former restored only 40–50% of the capacity while the latter restored approximately 90%. The electrochemical monitoring data provided a useful comparison of two repair systems in terms of inhibitive influence of repairs on steel reinforcement and electrochemical interactions between the repaired and unrepaired areas. The protection afforded to the corroded rebars and subsequent reduction in corrosion rate was more significant with free flowing micro-concrete repair material than with OPC mortar. Incipient anodes were formed at the repair/concrete interfaces soon after the repair. Under accelerated weathering conditions, free flowing micro-concrete has been found to offer better resistance to chloride ingress from an external source than OPC mortar. A significant increase in corrosion rate and concrete surface weathering was observed in the climatic chamber, hence suggesting that a long term performance of a repair material can be assessed in a short time scale under these conditions.
Article
The paper presents the results of a field investigation of repairs to two highway bridges. The repairs were applied by spraying onto unpropped compression members of the bridges. Two categories of commercial repair materials were used, low stiffness materials relative to the substrate (Erm < Esub) and high stiffness materials relative to the substrate (Erm > Esub). The repair materials also represented a range of other properties such as strength, density, shrinkage, and creep. The results show that repairs applied with relatively stiff materials, Erm > Esub, display efficient structural interaction with the structure. High stiffness repairs are effective in redistributing shrinkage strain to the substrate and attracting external loading in the long term. Low stiffness repair materials (Erm < Esub) are much more likely to undergo tensile cracking due to restrained shrinkage. Low stiffness repairs are ineffective in redistributing strain. 2000
Article
Cover title. Prepared as part of an investigation conducted by the Engineering Experiment Station, University of Illinois at Urbana-Champaign.
Seismic assessment and retrofit of reinforced concrete buildings
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Fib. Seismic assessment and retrofit of reinforced concrete buildings. State of Art Report, Bulletin 24. Federation International du Beton: Lausanne (Switzerland); 2003.
Model displacement in horizontal direction for P15 at debonding (left) and P50 at same vertical load level (right)
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Fig. 10. Model displacement in horizontal direction for P15 at debonding (left) and P50 at same vertical load level (right).
Straus7 user's manual. Sydney
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G+D Computing. Straus7 user's manual. Sydney; 2005.