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This paper presents the results of analytical studies concerning the flexuralstrengthening of reinforced concrete beams by external bonding of high-strength lightweightcarbon fiber reinforced plastic (CFRP) plates to tension face of the beam. Three groups of beamswere tested analytically and compared with existing experimental results. Results of the numericalanalyses showed that, although addition of CFRP plates to the tension face of the beam increasesthe strength, it decreases the beam ductility. Finite element modeling of fifteen different beams in aparametric study indicates that steel area ratio, CFRP thickness, CFRP ultimate strength andelastic modulus considerably influence the level of strengthening and ductility.

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In most cases, fiber reinforced self-compacting concrete (FRSCC) contains only one type of fiber. The use of two or more types of fibers in a suitable combination may potentially not only improve the overal properties of self-compacting concrete, but may also result in performance synergie. The combining of fibers, often called hybridization, is investigated in this paper for a cimentetious matrix. Control, single, two fibers hybrid composites were cast using different fiber type steel and polypropylene with different sizes. Flexural toughness tests were performed and results were extensively analysed to identify synergy, if any, associated with various fiber combinations. Based on various analysis schemes, the paper identifies fiber combinations that demonstrate maximum synergy in terms of flexural toughness.

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FRPs (fiber reinforced polymer) possess many favorable characteristics suitable and applicable for construction industry when compared with steel reinforcement. There are new ideas to use FRPs as longitudinal or transverse reinforcement for new concrete elements particularly for bridge decks or beams. Although high tensile strength of FRP is main characteristic for applications at both areas, its weakness to bending and linear stress-strain behavior with virtually no ductility, makes it vulnerable to probably premature failures under reversal tension-compression loading during earthquake. A pilot research project has been conducted to explore the characteristics of large-scale cantilever concrete beams reinforced with FRP re-bars and grids and were tested under either simulated cyclic loading or monotonically increasing lateral loading. This paper presents the test parameters and results obtained during research. The analytical relationships are compared with those recorded experimentally, and test results showed the diagonal cracks and either rupturing of FRP bars in tension or stability failure in compression bars at long or short shear span beams. The comparison of nominal moment capacities between analytical and experimental values confirms that plane section analysis is applicable to FRP reinforced concrete members.

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Clay soils and their related abnormal behavior such as excessive shrinkage, swelling, consolidation settlement and cracking on drying has been the subject of many investigations. Previous studies mainly evaluated the effects of additives such as lime, cement and sand on these characteristics. Initial results indicated that the soil characteristics were improved. However, reportedly in many cases, these additives resulted in a decrease in plasticity and increase in hydraulic conductivity. As a result, there has been a growing interest in soil/fiber reinforcement. The present investigation has focused on the impact of short random fiber inclusion on consolidation settlement, swelling, hydraulic conductivity, shrinkage limit and the development of desiccation cracks in compacted clays. To examine the possible improvements in the soil characteristics, samples consisting of 75% kaolinite and 25% montmorillonite were reinforced with 1, 2, 4 and 8 percent fibers as dry weight of soil with 5, 10 and 15mm lengths. Results indicated that consolidation settlements and swelling of fiber reinforced samples reduced substantially whereas hydraulic conductivities increased slightly by increasing fiber content and length. Shrinkage limits also showed an increase with increasing fiber content and length. This meant that samples experienced much less volumetric changes due to desiccation, and the extent of crack formation was significantly reduced.

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 Superior performances of Self-Compacting Concrete (SCC) in fresh state to achieve a more uniform distribution encourage the addition of fibers in concrete which is a motivation for structural application of fiberreinforced concrete. Fiber addition reduces the workability of Self-Compacting Fiber Reinforced Concrete (SCFRC). To provide required workability of the SCFRC, more paste is needed in the mixture. Therefore, the coarse aggregate content shall be adjusted to maintain its workability. The purpose of this study is to drive a model for estimating the aggregate contents for SCFRC. This model is based on constant covering mortar thickness theory. In this paper, all parameters which are participated in coarse aggregate content are discussed and presented in a relation. Then another relation is developed for predicting the void volume in the fibrous concrete. These relations are combined and a mathematical relation is deduced for predicting the coarse volume content in the function of the fiber factors. Proposed model is validated by conducting a rheological test. The result shows that the proposed model is simple, applicable and can be used as starting point in practical project.      Finally in order to complete the proposed model, another relation has been derived that can show the interaction of parameters involved in SCFRC rheology behavior. 

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The use of epoxy-bonded FRPcomposite for structural repair is emerging as an efficient and cost-effective technique for restoring and upgrading the capacity of concrete structures. Considerable researches have been reported in the last decades on the mechanical behavior and failure modes of the FRPstrengthened RC elements but actual data on its durability are scarce. This study intends to examine the durability of concrete specimens strengthened with FRP laminates under accelerated laboratory conditions and mimic harsh environmental situation which is the penetration of chloride ions. In this study three groups of specimens were examined. Each of these groups includes several concrete cylindrical specimens full confined with FRP laminates for investigating different types of fiber (Glass and Carbon), number of fiber layers and temperature influences. Furthermore, an apparatus was fabricated to simulate wetting and drying cycles for the second group of specimens. Moreover group III specimens were placed in a marine environment for 3 years to monitor their performance. Test results show that addition of FRP laminates reduces chloride ions penetration up to 70 percent. Results also indicate that although chloride ions penetration decreased the ultimate strength of cylindrical specimens up to 11 percent but FRP strengthened specimens achieved their initial strengths. Moreover wetting and drying cycles reduced the strength of cylinder specimens up to about ten percent especially in the high temperature laboratory condition.

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In recent years, different damage indexes have been introduced in engineering literature. The most prominent one among other

counterparts is the 1985 Park and Ang's damage index (DIPA), which demonstrates well calibration against experimental

results. Hence, it has traditionally had broad application in the field of structural engineering. Commonly, in DIPA relevant

parameters are assessed based on plastic-hinge approach, which is not well suited to consider the coupled response between

stress resultants (axial force and flexural moment) especially in grossly nonlinear domain. The reason is that named approach

is utilized constant shape plastic moment-curvature curve, which is not capable of varying the shape throughout loading history.

Another drawback of plastic-hinge method is the difficulty of representing precisely partial yielding of the cross-section. To

remedy the situation, the fiber discretization technique is used in this paper. Based on the fiber discretization strategy, not only

have the stiffness and strength degradation been characterized more accurately, but also the distribution of plasticity along the

plastic zone has been considered. Besides, the multi-directional effect of axial force and flexural moment is considered to assess

DI parameters. Additionally, this strategy directly incorporates the effect of transverse confinement into cross sectional

constitutive behaviour.

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In this study compressive strength of carbon nanotube (CNT)/cement composite is computed by analytical method. For this purpose representative elementary volume (REV) as an indicator element of composite is chosen and analyzed by elasticity relationships and Von mises' criterion applied to it. It is assumed that carbon nanotubes are distributed uniformly in the cement and there is perfect bonding in the interface of cement and nanotube. At first for simplicity of computations, carbon nanotubes ( CNTs) are assumed to have unidirectional orientation in the cement matrix. In following, the relations are generalized to consider random distribution of nanotubes in cement, and a new factor suggested for random orientation of fibers in the CNT/cement composite. The results of analytical method are compared with experimental results.

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One important application of fiber reinforced polymer (FRP) is to confine concrete as FRP jackets in seismic retrofit process

of reinforced concrete structures. Confinement can improve concrete properties such as compressive strength and ultimate axial

strain. For the safe and economic design of FRP jackets, the stress-strain behavior of FRP-confined concrete under monotonic

and cyclic compression needs to be properly understood and modeled. According to literature review, it has been realized that

although there are many studies on the monotonic compressive loading of FRP-confined concrete, only a few studies have been

conducted on the cyclic compressive loading. Therefore, this study is aimed at investigating the behavior of FRP-confined

concrete under cyclic compressive loading. A total of 18 cylindrical specimens of FRP-confined concretewere tested in uniaxial

compressive loading with different wrap thickness, and loading patterns. The results obtained from the tests are presented and

examined based on analysis of test results predictive equations for plastic strain and stress deterioration were derived. The

results are also compared with those from two current models,comparison revealed the lack of sufficient accuracy of the current

models to predict stress-strain behavior and accordingly some provisions should be incorporated.

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The main objective of this study is to drive a simple solution for prediction of steel fiber reinforced concrete (SFRC) behavior

under four point bending test (FPBT). In this model all the force components at the beam section (before and after cracking)

are formulated by applying these assumptions: a bilinear elastic-perfectly plastic stress-strain response for concrete behavior

in compression, a linear response for the un-cracked tension region in a concrete constitutive model, and an exponential

relationship for stress-crack opening in the crack region which requires two parameters.Then the moment capacity of the critical

cracked section is calculated by applying these assumptions and satisfying equilibrium lawat critical cracked section. After that,

parametric studies have been done on the behavior of SFRC to assess the sensitively of model. Finally the proposed model has

been validated with some existing experimental tests.The result shows that the proposed solution is able to estimate the behavior

of SFRC under FPBT with simplicity and proper accuracy.

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The aim of current study is to investigate the effect of Carbon Fiber Reinforced Polymer (CFRP) composites on the fatigue

response of reinforced concrete beams. 6 reinforced concrete (RC) beams from which 3 were retrofitted with CFRP sheets, were

prepared and subjected to fatigue load cycles. To predict and trace the failure occurrence and its growth, a small notch was

induced at the middle span in bottom surface of all RC specimens. At the certain points, strains in concrete and CFRP were

measured in each cycle. The upper limit of applied load was considered at the level of design service load of bridges. In addition,

strain measurements facilitated to the calculation of interfacial shear stresses between concrete substrate and the CFRP layer.

The variation of such stresses through load cycles has been presented and discussed. Also, a discussion on possibility of the local

debonding phenomenon resulted from such interfacial stresses was presented. Load–deflection curves, strain responses and

propagation of tensile cracks provided an insight on the performance of the CFRP strengthened beams subjected to different

cycles of fatigue loading. Variation of load-deflection curves through fatigue load cycles depicted stiffness degradation which

was discussed in the research.

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Worldwide, asbestos fibers utilized in fiber cement boards, have been recognized as harmful materials regarding the public health and environmental pollutions. These concerns motivate the researchers to find the appropriate alternatives to substitute the asbestos material towards the sustainability policies. In this paper, the applicability of asbestos replacement with three types of agricultural waste fibers, including bagasse, wheat and eucalyptus fibers were experimentally investigated. To this end, the flexural behaviour and microstructure of cement composite boards made by addition of 2 % and 4 % of waste agricultural fibers in combination with and without 5 % replacement of silica fume by mass of cement were evaluated. The results of this study attested the applicability of utilized waste agricultural fibers in production of cement composite boards by improving the flexural and energy absorption characteristics, more or less, depending on the type of fibers. Moreover, it is found that application of silica fume in production of cement composite boards led to an increase in flexural strength.

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Abstract: This paper presents the influence of adding steel fibers and incorporation of silica fume on the mechanical properties of high-strength concrete. The variables investigated were steel fiber volume fraction (0 to 1.5%), silica fume replacement (5, 10 and 15%) and water-to-binder ratio (0.25, 0.30, 0.35 and 0.40). The influence of fiber content in terms of fiber reinforcing index on the compressive and splitting tensile strengths of high-strength steel fiber reinforce concrete (HSFRC) is presented. The use of silica fume increased both the compressive and splitting tensile strengths of concrete at 28 days. On the other hand, the addition of crimped steel fiber into high-strength concrete improves splitting tensile strength significantly. Based on the test data, using regression analysis, empirical expression to predict 28-day tensile strength of HSFRC in terms of fiber reinforcing index was developed and the absolute variation and integral absolute error (IAE) obtained was 3.1% and 3.3, respectively. The relationship between splitting tensile and compressive strength of SFRC was reported with regression coefficient (r) = 0.9. The experimental values of previous researchers were compared with the values predicted by the model and found to predict the values quite accurately.

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Soil reinforced with fiber shows characteristics of a composite material, in which fiber inclusion has a significant effect on soil permeability. Concerning to the higher void ratio of carpet fibers, at first stages it may be expected that an increase in fiber content of the reinforced soil would result in an increase in permeability of the mixture. However, the present article demonstrates that fiber inclusion will decrease the permeability of sand-fiber composite.A series of constant head permeability tests have been carried out to show the effects and consequently, a new system of phase relationships was introduced to calculate the dry mass for the sand portion of the composite. Monte Carlo simulation technique adopted with finite element theory was employed to back calculate the hydraulic conductivity of individual porous fibers from the laboratory test results. It was observed that the permeability coefficient of the porous fibers are orders of magnitude less than the skeletal sand portion due to the fine sand particle entrapment and also the fiber volume change characteristics.

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The total coal and lignite consumption of the thermic power plants in Turkey is approximately 55 million tons and nearly 15 million tons of fly ash is produced. The remarkable increase in the production of fly ash and its disposal in an environmentally friendly manner is increasingly becoming a matter of global concern. Studies for the utilization of fly ash in Turkey are necessary to reduce environmental problems and avoid economical loss caused by the disposal of fly ash. Efforts are underway to improve the use of fly ash in several ways, with the geotechnical utilization also forming an important aspect of these efforts. An experimental program was undertaken to investigate the effects of Multifilament (MF19average) and Fibrillated (F19average) polypropylene fiber on the compaction and strength behavior of CH class soil with fly ash in different proportions. The soil samples were prepared at three different percentages of fiber content (i.e. 0.5%, 1% and 1.5% by weight of soil) and two different percentages of fly ash (i.e. 10% and 15% by weight of soil). A series of tests were prepared in optimum moisture content and laboratory unconfined compression strength tests, compaction tests and Atterberg limits test were carried out. The fiber inclusions increased the strength of the fly ash specimens and changed their brittle behavior into ductile behavior.

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An experimental study on the impact performance of silica fume concrete and steel fiber reinforced concrete at 28 days and 56 days under the action of repeated dynamic loading was carried out. In this experimental investigation, w/cm ratios of 0.4 and 0.3, silica fume replacement at 10% and 15% and crimped steel fibers with an aspect ratio of 80 were used. Results indicated that addition of fibers in high-performance concrete (HPC) can effectively restrain the initiation and propagation of cracks under stress, and enhance the impact strengths, toughness and ductility of HPC. Pulse velocity test was carried out for quality measurements of high-performance steel fiber reinforced concrete. Steel fibers were observed to have significant effect on flexural strength of concrete. The maximum first crack strength and ultimate failure strength at 28 days were 1.51 times and 1.78 times, respectively at 1.5% volume fraction to that of HPC. Based on the experimental data, failure resistance prediction model was developed with correlation coefficient (R) = 0.96 and absolute variation determined is 1.82%.

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The current research intends to study the possibility of producing fiber recycled self-compacting concrete (FRSCC) using demolitions as a coarse aggregate (crushed red brick and crushed ceramic). Steel fibers were used in recycled self-compacting concrete (RSCC) to improve fresh and hardened properties of this type of concrete. Thirty nine concrete mixes were prepared to achieve the aim proposed in this paper. Steel fiber volume fraction varied from 0 to 2.0% by the volume of concrete with aspect ratio 65. The fresh properties of FRSCC were evaluated using slump flow, J-ring and V-funnel tests. Compressive strength, tensile strength, flexural strength and density tests were performed in order to investigate mechanical properties. The optimum volume fraction of steel fibers was 0.25% and 1.0% for the mixes contained crushed red brick and ceramic as a coarse aggregate respectively. At optimum content of steel fibers, the compressive strength for the RSCC mixes with steel fibers improved by 11.3% and 31.8% for the mixes with crushed ceramic and crushed red brick, respectively with respect to control mix. Also the tensile strength and the flexural strength for the mixes were improved

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Fiber Reinforcement Concrete is mainly distinguished in their behavior in cracked tension zone which is called tension softening behavior. Wide researchers have been investigated this behavior and present many tensioned softening models. This paper presents a compression between four tension softening models including constant, linear, bilinear and exponential models in flexural behavior. In this study the behavior of rectangular beam section under four/three point bending test have been predicted by iteration procedure. These models has been compared in some parametrical properties. The result of this study shows variety in result for four used models and indicate concern in applied assumptions.