• Magazine of the Korea Concrete Institute
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• v.4 no.1
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• pp.107-118
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• 1992

In order to examine the mechanical properties of carbon fiber reinforced cement composites with silica powder PAN - based carbon fiber and Pitch- based carbon fiber, and polymer impregnators experimental studies on CFRC impregnated in polymer were carried out. The effects of types, length, and content~i of carbon fibers and matrices of fresh and hardened CFRC impregnated in polymer were examined. The test results show that compressive, tensile, and flexural strength of CFRC impregnated in polymer were much more iriCreased than those of air cured and autodaved CFIIC CFRC impregnated in polymer was also considerably effective in improving toughness, freeze thaw resistance, loss of shrinkage, and creep resist ance, compared with air cured and autoclaved CFRC.

• Structural Engineering and Mechanics
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• v.26 no.4
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• pp.427-439
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• 2007

The exploitation of fibre reinforced polymer composites, as external reinforcement is an evergreen and well-known technique for improving the structural performance of reinforced concrete structures. The demand to use FRP composites in the civil engineering industry is mainly due to its high strength, light weight, and stiffness. This paper exemplifies the shear strength of partially precracked reinforced concrete rectangular beams repaired with externally bonded Bi-Directional Carbon Fibre Reinforced Polymer (CFRP) Fabrics strips. All specimens were cast in the laboratory environment without any internal shear reinforcement. The test parameters were longitudinal tensile reinforcement, shear span to effective depth ratio, spacing of CFRP strips, and orientation of CFRP reinforcement. It mainly focuses on the shear capacity and modes of failure of the CFRP strengthened shear beams. Results have shown that the CFRP repaired beams attained a shear enhancement of 32% and 107.64% greater than the control beams. This study underscores that the CFRP strip technique significantly enhanced the shear capacity of precracked reinforced concrete rectangular beams without any internal shear reinforcement.

• Structural Engineering and Mechanics
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• v.30 no.4
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• pp.403-426
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• 2008

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

• KEPCO Journal on Electric Power and Energy
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• v.1 no.1
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• pp.127-134
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• 2015

Recently, the external bonding of carbon fiber reinforced polymer (CFRP) sheets has come to be regarded as a very effective method for strengthening of reinforced concrete structures. The behavior of CFRP-strengthened RC structure is mainly governed by the interfacial behavior, which represents the stress transfer and relative slip between concrete and the CFRP sheet. In this study, the effects of bonded length, width and concrete strength on the interfacial behavior are verified and a bond-slip model is proposed. The proposed bond-slip model has nonlinear ascending regions and exponential descending regions, facilitated by modifying the conventional bilinear bond-slip model. Finite element analysis results of interface element implemented with bond-slip model have shown good agreement with the experimental results performed in this study. It is found that the failure load and strain distribution predicted by finite element analysis with the proposed bond-slip are in good agreement with results of experiments.

• Journal of the Korea Concrete Institute
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• v.17 no.3 s.87
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• pp.411-418
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• 2005

Polymer-modified mortar and concrete are prepared by mixing either a polymer or monomer in a dispersed, or liquid form with fresh cement mortar and concrete mixtures, and subsequently curing, and if necessary, the monomer contained in the mortar or concrete is polymerized in situ. Although polymers and monomers in any form such as latexes, water-soluble polymers, liquid resins, and monomers are used in cement composites such as mortar and concrete, it is very important that both cement hydration and polymer phase formation proceed well the yield a monolithic matrix phase with a network structure in which the hydrated cement phase and polymer phase interpenetrate. In the polymer-modified mortar and concrete structures, aggregates are bound by such a co-matrix phase, resulting in the superior properties of polymer-modified mortar and concrete compared to conventional mortar and concrete. The purpose of this study is to obtain the necessary basic data to develope appropriate latexes as cement modifiers, and to clarify the effects of the monomer ratios and amount of emulsifier on the properties of the polymer-modified mortars using methyl methacrylate-butyl acrylate(MMA/BA) and methyl methacrylate-ethyl acrylate(MMA/EA) latexes. The results of this study are as follows, the water absorption, chloride ion penetration depth and carbonation depth of MMA/BA-modified mortar are lowest. However, they are greatly affected by the polymer-cement ratio rather than the bound MMA content and type of polymer.

• Applied Chemistry for Engineering
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• v.28 no.3
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• pp.360-368
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• 2017

In order to investigate the durability of high performance polymer concrete composites, polymer concrete specimens were prepared using the ortho-type unsaturated polyester resin (UPR) and iso-type UPR as a polymer binder and the calcium carbonate and silica fine powder as a filler. The durability of polymer concrete specimens was measured by hot water resistance, chemical resistance, pore analysis and SEM observation. The compressive strength of the specimen using the iso-type UPR was higher than that of using the ortho-type UPR, and the compressive strength of the specimen using the silica fine powder was higher than that of using the calcium carbonate filler. From hot water resistance results, it was found that the specimen using the iso-type UPR was superior to that of using the ortho-type UPR and the specimen using the calcium carbonate filler was superior to that of using the silica fine powder. The compressive strength reduction rate was measured after the chemical resistance test and the sodium hydroxide solution showed the highest reduction rate, followed by sulfuric acid, hydrochloric acid and calcium chloride solutions. When using the alkaline solution of sodium hydroxide, the weight reduction rate of the specimen using calcium carbonate was lower than that of using silica fine powder, while for the acidic solutions of sulfuric acid and hydrochloric acid, the weight reduction rate of the specimen using the silica fine powder was lower than that of using calcium carbonate.

• Steel and Composite Structures
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• v.9 no.6
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• pp.569-584
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• 2009

Corrosion of steel rebars in bridge decks which are faced to harsh conditions, is a common problem in construction industries due to the porosity of concrete. In this research, the behavior of one-way concrete slabs reinforced with Glass fiber reinforced polymer (GFRP) molded grating is investigated both theoretically and experimentally. In the analytical method, a closed-form solution for load-deflection behavior of a slab under four-point bending condition is developed by considering a concrete slab as an orthotropic plate and defining stiffness coefficients in principal directions. The available formulation for concrete reinforced with steel is expanded for concrete reinforced with GFRP molded grating to predict ultimate failure load. In finite element modeling, an exact nonlinear behavior of concrete along with a 3-D failure criterion for cracking and crushing are considered in order to estimate the ultimate failure load and the initial cracking load. Eight concrete slabs reinforced with steel and GFRP grating in various thicknesses are also tested to verify the results. The obtained results from the models and experiments are relatively satisfactory.

• Computers and Concrete
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• v.20 no.2
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• pp.165-176
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• 2017

Textile Reinforced Cementitious Composite (TRCC) became the most common construction material lately and have excellent properties. TRCC can be employed in the manufacture of thin-walled facade elements, load-bearing integrated formwork, tunnel linings or in the strengthening of existing structures. These composite materials are a combination of matrix and textile materials. There isn't much research done about the usage of polymer modified matrices in textile reinforced cementitious composites. In this study, matrix materials named as fine grained concretes ($d_{max}{\leq}1.0mm$) were investigated. Air entraining effect of polymer modifiers were analyzed and air void content of fine grained concretes were identified with different methods. Aim of this research is to study the effect of polymer modification on the air content of fine grained concretes and the role of defoamer in controlling it. Polymer modifiers caused excessive air entrainment in all mixtures and defoamer material successfully lowered down the air content in all mixtures. Latex polymer modified mixtures had higher air content than redispersible powder modified ones. Air void analysis test was performed on selected mixtures. Air void parameters were compared with the values taken from air content meter. Close results were obtained with tests and air void analysis test found to be useful and applicable to fine grained concretes. Air void content in polymer modified matrix material used in TRCC found significant because of affecting mechanical and permeability parameters directly.

• Journal of the Korea Institute of Building Construction
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• v.9 no.5
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• pp.71-77
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• 2009

In a range of forms, such as latex, water-soluble polymer, liquid resin, and monomer, polymer dispersions have been widely used in the construction industry as cement modifiers because of their excellent properties, such as acid-resistance, water-proofness, and good ductility in mortar and concrete. Polymer cement slurry (polymer-modified slurry) is made of cement and polymer dispersions, with a high polymer-cement ratio of 50% or more. The purpose of this study is to evaluate the water permeability and drying shrinkage of polymer cement mortar (polymer-modified mortar) and cement concrete coated by polymer cement slurry. The polymer cement mortar and cement concrete are prepared with various polymer types, polymer-cement ratios and curing methods, and are tested for water permeability, drying shrinkage and strength. The test results showed thatthe weight of permeable water of polymer cement mortar decreases with an increase in the polymer-cement ratio, reaching a minimum at the polymer-cement ratio of 20%. In particular, the weight of permeable water of St/BA-modified mortar with a polymer-cement ratio of 20% coated with St/BA-modified slurry is about 1/55 that of unmodified mortar. The EVA- and St/BA-modified slurries coated on cement concrete have about 4 or 5 times higher drying shrinkage compared to cement concrete. The strength of polymer cement mortars tends to increase with a higher polymer-cement ratio, and is considerably higher than that of unmodified mortar. It is thus concluded that polymer cement mortars coated by polymer cement slurry are effective for industrial application, and have superior properties such as waterproofness and strengths, compared with conventional cement mortar.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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• pp.333-336
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• 2006

In general, polymer materials undergo degradation when exposed to ultraviolet radiation, which can cause dissociation of chemical bonds. FRP composites which are used in strengthening existing structure are usually adhered on the concrete surface, its mechanical properties as well as appearance such as color, surface conditions are affected by sunlight and expecially ultraviolet light. In this study, variations of tensile strength after exposure for certain period of time through accelerated exposure by Xe arc methods specified in KS F 2274 are measured in order to examine strength degradation characteristics of FRP composite. As a result of ultraviolet light test for FRP composite after accelerated exposure for 0, 500, 1000, 1500 hour, discoloration of FRP composite occurs according to the passage of time. But, few strength degradations of FRP composite are observed due to exposure of ultraviolet ray with an small variation of tensile strength.