• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.3
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• pp.65-73
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• 2013

Recently the exterior attaching reinforcement method is being often used by using FRP (Fiber Reinforced Polymer) as a method of strengthening concrete structure. this FRP exterior attaching reinforcement method has several advantages like high intensity, stiffness, good durability and easy installment comparing to its weight. but its structure is airtight covered by reinforcement material whose water permeability is low and water can't be discharged, thus it may provoke a damage to the structure after a long while. the main purposes of this study are to develop GFRP reinforcement material which can discharge the surface water properly and to measure its special functions. for this, we have changed the normal reinforcement material to water permeable structure and measured its water permeance modulus by an indoor test which shows the process of water permeance with the parameter of contained GFRP quantity. also tried to verify the measured value of the water permeance modulus in theory by analyzing the numbers on water permeance process. the test result showed that the biggest quantity of water, 0.5129 g/h $m^2$ was discharged when the fiber contained quantity reached at 75% and the tensile strength was also biggest by 476.6MPa at 75%, so it appeared that COSREM GP panel with 75% fiber contained quantity is the best in ventilation and structure.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.6
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• pp.21-30
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• 2013

As increasing number of large-size earthquake, the social interest of seismic retrofitting of RC structure is growing. Especially, the RC columns that are not reflected seismic design can not resist lateral loads by the earthquake. The brittle fracture of Non-seismic designed columns lead to full collapse of the building. Thus, the emergency columns reinforcement method is needed. That have a fast construction time, do not cause damage to the column. In the past, cross-sectional expansion method, a steel plate reinforcing method is applied mainly, but in recent years, carbon fiber sheet taking advantage of FRP (Fiber Reinforced Polymer) is widely used. In this study, retrofitting effect of seismic performance of FRP seismic reinforcement, which is possible to emergency construction, was examined. Reinforced concrete specimens were constructed to experimental study. The seismic performence of specimes retrifitted with FRP seismic reinforcement were evaluated. As a result, the seismic performance of specimen reinforced with FRP seismic reinforcement has been improved.

• Polymer(Korea)
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• v.36 no.2
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• pp.208-215
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• 2012

To study the effect of surface crosslinked layer on the crosslinked poly(sodium acrylate) (cPSA) absorbent, we synthesized several surface crosslinked cPSAs with 5, 10 and 20 g of ethylene glycol dimethacrylate (EGDMA) by an inverse emulsion polymerization method to delay the absorption of excess water in concrete. We measured the compressive and flexural strength of mortars having 0.5, 1.0 and 1.5 wt% cPSA-EGDMA. We observed the increase of compressive and flexural strength of the cPSA-EGDMA added cement mortars except for the 0.5 wt% cPSA-EGDMA (20 g) added cement mortar. 1.0 wt% cPSA-EGDMA (5 g) added cement mortar showed about 16% and 10% increased compressive and flexural strength than those of plain cement mortar. To study the effect of porosity on compressive and flexural strength, we used FE-SEM and porosimeter. FE-SEM analysis showed swollen cPSMAEGDMA (5 g) filled between calcium silicate hydrate (C-S-H) crystals. We observed the decreased porosity of the cPSA-EGDMA added cement mortars than that of plain cement mortar. 1.0 wt% cPSA-EGDMA (5 g) cement mortar showed the lowest porosity of 16.5%.

• Polymer(Korea)
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• v.35 no.4
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• pp.363-369
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• 2011

To study the effect of incorporation of a surface crosslinking layer on a crosslinked poly (sodium acrylate) (cPSA) absorbent with ethylene glycol dimethacrylate CEGDMA), we synthesized several surface crosslinked cPSAs with EGDMA by an inverse emulsion polymerization method to delay the absorption of excess water in concrete, Liquid paraffin was used as a continuous phase. cPSA was synthesized with acrylic acid (AA) neutralized with aqueous 8 M sodium hydroxide solution as a monomer, N,N-methylene bisacrylamide (MBA) as crosslinking agent and ammonium persulfate (APS) and sodium metabisulfite (SMBS) as a redox initiator system by inverse emulsion polymerization. FTIR spectroscopy was used to characterize $Ca^{2+}$ ion interaction with cPSA and cPSA-EGDMAs. The swelling ratios of synthesized absorbents were evaluated from the absorption in deionized water, cement saturated aqueous solution and aqueous solution of calcium hydroxide (pH 12). Equilibrium swelling times for cPSA and surface crosslinked cPSA with EGDMA were 2 and 3 hrs, respectively. We also observed an increase in setting time of the cement and an increase in the compressive strength of mortar by addition of the synthesized cPSA-EGDMA.

• Journal of the Korea Concrete Institute
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• v.21 no.2
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• pp.139-146
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• 2009

Experimental study was performed to evaluate the long-term behavior of CFRP (carbon fiber reinforced polymer) strips under sustained loads including prestressing force in strengthening RC members with post-tensioned CFRP strips. Two types of CFRP strip such as unidirectional CFRP strip and hybrid CFRP strip which is composed of carbon fiber and steel plate were considered. Also two types of loading scheme were included in this study. Direct sustained loading test had been carried out to estimate the creep deformation and relaxation of CFRP strips including slip deformation at both mechanical anchorages for over 700 days. Also, flexural sustained loading test had been conducted to estimate the initial prestress losses on clamping the CFRP strips at jacking anchorages for over 90 days. From the sustained loading tests, it was observed that stress losses of unidirectional CFRP strips due to the creep deformation and relaxation of material itself and slip deformation at mechanical anchorage were ignorable. On the other hand, significant stress losses caused by the yielding of steel embedded in CFRP strips were found in case of hybrid CFRP strips due to the initial jacking force over steel yielding stress. Also, initial prestress losses during setting of CFRP strips on mechanical anchorage were about 10% of intial jacking force, which must be considered in the design.

• Journal of the Korean Society of Radiology
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• v.7 no.1
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• pp.45-50
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• 2013

Non-invasive technique CT, called automated computed tomography, is used to detect lesion of a patient when diagnosing human body. Information obtained from CT plays an important role in assembling 3 dimensional images. Recently, new equipment, operated by CT, is required which can be appliable to physical and biological research. In accordance to this quest, micro-CT is invented that produce more detail and concrete information. Images supplied by CT are even more detailed and concrete, so it contributes much to the development of biology and polymer material engineering field. However, there has been little reliable reports regarding measuring information of space dose distribution about exposure dose limit of users operating micro-CT. In addition, little reports regarding space dose distribution of exposure has been known about unwanted diffraction light produced by usage of micro-CT. The exterior of micro-CT is covered by lead, which is for removing exposure of diffraction light. Thus, even if it is good enough to prevent exposure of diffraction light, consistent management of equipment will be required as time goes by and equipment are getting old as well. We measured space dose distribution regarding exposure of diffraction light of users operating micro-CT directly. Therefore, we suggest that proper management should be necessary for users operating micro-CT not to be exposed by unwanted diffraction light.

• Journal of the Korea Concrete Institute
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• v.19 no.6
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• pp.677-684
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• 2007

This study investigates the failure mechanism of RC beams strengthened with GFRP (glass fiber reinforced polymer) sheets. After analyzing failure mechanisms, the various methods to prevent the debonding failures, such as increasing bonded length of GFRP sheets, U-shape wrappings and epoxy shear keys are examined. The bonded length of GFRP sheets are calculated based on the assumed bond strengths of epoxy resin. The U-shape wrappings are either adopted at the end or center of the CFRP sheets bonded to the beam soft. The epoxy shear keys are embedded to the beam soft to provide sufficient bond strength. The end U-wrappings and the center U-wrappings are conventional, while epoxy shear keys are new details developed in this study. A total six half-scale RC beams have been constructed and tested to investigate the effectiveness of each methods to prevent debonding failure of GFRP sheets. From the experimental results, it was found that increasing bonded length or end U-wrappings do not prevent debonding failure. On the other hand, the beams with center U-wrappings and shear keys reached an ultimate state with their sufficient performance. The center U-wrappings tended to control debonding of the longitudinal GFRP sheets because the growth of the longitudinal cracks along the edges of the composites was delayed. In the case of shear keys, it was sufficient to prevent debonding and the beam was failed by GFRP sheets rupture.

• Journal of the Korea Concrete Institute
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• v.20 no.6
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• pp.765-772
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• 2008

For RC structures, long-term deformation occurs due to the inherent characteristics, which are creep and shrinkage. In terms of serviceability, it is important to limit deflection caused by the deformation to the allowable deflection. In the recent years, various repair and strengthening methods have been used to improve performance of the existing RC structures. One of the typical methods is FRP externally bonded method (EBR). Fiber reinforced polymer (FRP) has been used worldwide as repair and strengthening materials due to its superior properties. Besides, it has to offer improved strengthening performance not only under instantaneous load but sustained load. Therefore, accurate prediction method of deflection for the RC members externally bonded with FRP under sustained load is required. In this paper, three beams were fabricated. Two beams were externally strengthened with one of CFRP plate and GFRP plate respectively. Total three beams were superimposed under sustained load of 25 kN. During 470 days, deflections at midspan were obtained. Moreover, creep coefficients and shrinkage strains were calculated by using ACI-209 code and CEB-FIP code. In order to predict the deflection of the beams, EMM, AEMM, Branson's method and Mayer's method were used. Through the experiment, it was found that the specimen with CFRP plate has the most flexural capacity and Mayer's method is the most precise method to predict total long-term deflections.

• International Journal of Highway Engineering
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• v.20 no.1
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• pp.87-95
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• 2018

PURPOSES : A geo-grid pavement, e.g., a stress-absorbing membrane interlayer (SAMI), can be applied to an asphalt-overlay method on the existing surface-pavement layer for pavement maintenance related to reflection cracking. Reflection cracking can occur when a crack in the existing surface layer influences the overlay pavement. It can reduce the pavement life cycle and adversely affect traffic safety. Moreover, a failed overlay can reduce the economic value. In this regard, the objective of this study is to evaluate the bonding properties between the rigid pavement and a SAMI by using the direct shear test and the pull-off test. The predicted fractural energy functions with the shear stress were determined from a numerical analysis of the moving average method and the polynomial regression method. METHODS : In this research, the shear and pull-off tests were performed to evaluate the properties of mixtures constructed using no interlayer, a tack-coat, and SAMI with fabric and without fabric. The lower mixture parts (describing the existing pavement) were mixed using the 25-40-8 joint cement-concrete standard. The overlay layer was constructed especially using polymer-modified stone mastic asphalt (SMA) pavement. It was composed of an SMA aggregate gradation and applied as the modified agent. The sixth polynomial regression equation and the general moving average method were utilized to estimate the interlayer shear strength. These numerical analysis methods were also used to determine the predictive models for estimating the fracture energy. RESULTS : From the direct shear test and the pull-off test results, the mixture bonded using the tack-coat (applied as the interlayer between the overlay layer and the jointed cement concrete) had the strongest shear resistance and bonding strength. In contrast, the SAMI pavement without fiber has a strong need for fractural energy at failure. CONCLUSIONS : The effects of site-reflection cracking can be determined using the same tests on cored specimens. Further, an empirical-mechanical finite-element method (FEM) must be done to understand the appropriate SAMI application. In this regard, the FEM application analy pavement-design analysis using thesis and bonding property tests using cored specimens from public roads will be conducted in further research.

• International Journal of Highway Engineering
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• v.11 no.3
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• pp.23-32
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• 2009

In this paper an experimental program was launched to determine the mechanical and durability properties of spall repair materials (RCC: 3 items, PCC: 2 items, PC: 3 items). Test items were mechanical property tests such as setting times, strengths, modulus of elasticity, plastic shrinkage, and durability tests such as dynamic modulus ratio, bond property with freeze-thaw, water absorption, chemical resistance, ultraviolet exposure. Modulus of the PC products exhibits ductile while the modulus is in the order of RCC > PCC > PC. At early ages the PC products experience higher plastic shrinkage than others, henceforth stable at 28 days. Other test results such as dynamic modulus ratio, absorption, and chemical resistance show that the PCs are superior to the PCCs and the RCCs. Except for PC-2, all patch materials had bond strength more than 1.3MPa after freeze-thaw cycles of 200~300 while the PCs and the PCCs seem to be better than the RCCs. With 500 hours of ultraviolet exposure, all patch materials showed to have no crack or deterioration at the surface.