• Title/Summary/Keyword: crack evaluation

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Evaluation of Chemical Resistance Performance of Synthetic Rubber and Cement Based Injection Repair Materials Used in Underground Concrete Structures (지하 콘크리트 구조물에 적용되는 합성고무계 및 시멘트계 주입형 보수재료의 화학 저항성능평가)

  • Kim, Soo-Yeon;Lee, Yeon-Sil;Song, Je-Young;Kim, Byoungil;Oh, Sang-Keun
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.21 no.5
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    • pp.148-155
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    • 2017
  • In this study, by using the international standards ISO TS 16774, Part 2 Test method for chemical resistance as a quality control method of injection type repair material used for leakage crack of underground concrete structure, the performance requirement against of chemical environment of underground concrete structures for repair materials was tested. For this testing 3 types for each of the 2 classes of repair materials(synthetic rubber, cement), with a total of 9 types repair materials, were selected and examined. As a result, the test results showed that the smallest performance deterioration by the change in the mass was with the synthetic rubber(RG) type as opposed to the cement type system, showing that the synthetic rubber type had the strongest relative resistance to chemical exposure. Furthermore, it is necessary to investigate the material with high resistance to chemical substances and to examine the material which can increase resistance to sodium hydroxide and sodium chloride in cement system. These results can be used as a basic index for the selection of repair materials with the strongest resistance to chemical environment found in concrete structures. In addition, it is expected that the test results derived in this study can be used as reference data that can be reflected in the quality improvement of the maintenance material to be developed later.

Improvement and Evaluation of Seismic Performance of Reinforced Concrete Exterior Beam-Column Joints Retrofitting with Fiber Reinforced Polymer Sheets and Embedded CFRP Rods (섬유시트와 매입형 CFRP Rod를 보강한 R/C 외부 보-기둥 접합부의 내진성능 평가 및 개선)

  • Ha, Gee-Joo;Ha, Young-Joo;Kang, Hyun-Wook
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.19 no.2
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    • pp.151-159
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    • 2015
  • In this study, experimental research was carried out to evaluate and improve the seismic performance of reinforced concrete beam-column joint regions using strengthening materials (CFRP sheet, AFRP sheet, embedded CFRP rod) in existing reinforced concrete structure. Therefore it was constructed and tested seven specimens retrofitting the beam-column joint regions using such retrofitting materials. Specimens, designed by retrofitting the beam-column joint regions of existing reinforced concrete structure, were showed the stable failure mode and increase of load-carrying capacity due to the effect of crack control at the times of initial loading and confinement of retrofitting materials during testing. Specimens LBCJ-CRUS, designed by the retrofitting of CFRP Rod and CFRP Sheet in reinforecd beam-column joint regions were increased its maximum load carrying capacity by 1.54 times and its energy dissipation capacity by 2.36 times in comparison with standard specimen LBCJ for a displacement ductility of 4 and 7. And Specimens LBCJ-CS, LBCJ-AF series were increased its energy dissipation capacity each by 2.04~2.34, 1.63~3.02 times in comparison with standard specimen LBCJ for a displacement ductility of 7.

Improvement and Seismic Performance Evaluation of RC Exterior Beam-Column Joints Using Recycled Coarse Aggregate with Hybrid Fiber (순환굵은골재 치환과 하이브리드섬유 혼입에 따른 철근콘크리트 외부 보-기둥 접합부의 내진성능 평가 및 개선)

  • Ha, Jae-Hoon;Ha, Gee-Joo;Shin, Jong-Hak
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.19 no.2
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    • pp.160-169
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    • 2015
  • In this study, experimental research was carried out to improve the seismic performance of reinforced concrete exterior beam-column joint regions using replacing recycled coarse aggregate with hybrid fiber (steel fiber+PVA fiber) in existing reinforced concrete building. Therefore it was constructed and tested seven specimens retrofitting the beam-column joint regions using such retrofitting materials. Specimens, designed by retrofitting the beam-column joint regions of reinforced concrete building, were showed the stable failure mode and increase of load-carrying capacity due to the effect of crack control at the times of initial loading and bridge of retrofitting hybrid fiber during testing. Specimens BCJGPSR series, designed by the retrofitting of replacing recycled coarse aggregate with hybrid fiber in reinforecd beam-column joint regions were increased its maximum load carrying capacity by 1.01~1.04 times and its energy dissipation capacity by 1.06~1.29 times in comparison with standard specimen BCJS. Also, specimen $BCJGPSR_1$ were increased its energy dissipation capacity by 1.33~1.65 times in comparison with specimens BCJS, BCJP and BCJGPR series for a displacement ductility of 9.

Interfacial Evaluation and Microfailure Sensing of Nanocomposites by Electrical Resistance Measurements and Wettability (전기저항측정법 및 젖음성을 이용한 나노복합재료의 미세파손 감지능 및 계면물성 평가)

  • Park, Joung-Man;Kwon, Dong-Jun;Shin, Pyeong-Su;Kim, Jong-Hyun;Baek, Yeong-Min;Park, Ha-Seung
    • Composites Research
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    • v.30 no.2
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    • pp.138-144
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    • 2017
  • Damage sensing of polymer composite films consisting of poly(dicyclopentadiene) p-DCPD and carbon nanotube (CNT) was studied experimentally. Only up to 1st ring-opening polymerization occurred with the addition of CNT, which made the modified film electrically conductive, while interfering with polymerization. The interfacial adhesion of composite films with varying CNT concentration was evaluated by measuring the wettability using the static contact angle method. 0.5 wt% CNT/p-DCPD was determined to be the optimal condition via electrical dispersion method and tensile test. Dynamic fatigue test was conducted to evaluate the durability of the films by measuring the change in electrical resistance. For the initial three cycles, the change in electrical resistance pattern was similar to the tensile stress-strain curve. The CNT/p-DCPD film was attached to an epoxy matrix to demonstrate its utilization as a sensor for fracture behavior. At the onset of epoxy fracture, electrical resistance showed a drastic increase, which indicated adhesive fracture between sensor and matrix. It leads to prediction of crack and fracture of matrix.

A Study on Aggregate Gradation of 10 mm Dense-graded Asphalt Mixture using Slag Aggregate (슬래그 골재를 사용한 10 mm 밀입도 아스팔트 혼합물의 골재입도 기준 연구)

  • Jo, Shin Haeng;Kim, Kyungnam;Kim, Nakseok
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.35 no.6
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    • pp.1367-1375
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    • 2015
  • The purpose of this paper is to suggest 10 mm aggregate specification for thin layer asphalt pavement using steel slag. Aggregate gradations of conventional dense-graded asphalt mixtures were made by fuller's model, whereas 10 mm dense-graded asphalt mixture was obtained tender mix due to close to the maximum density line. The proposed aggregate gradation specification was made to have enough VMA and well-interlocking refer to foreign standards. The correlation between the proposed aggregate gradation and the properties of mixtures were analyzed using Gradation Ratio (GR) and Compacted Aggregate Density (CAD). The CAD index has a high $R^2$ of 0.86-0.99 because the CAD index is able to reflect various aggregate properties. As the results of evaluation by CAD index the proposed aggregate gradation provides more reliable stability and VMA. The percent passing (%) of aggregate size smaller than 0.3 mm was limited 10% or more for improving crack resistance. This limitation increased for 15% of the asphalt mixture's toughness.

Experimental Evaluation on Shear Strength of High-Strength RC Deep Beams (고강도 철근콘크리트 깊은 보의 전단 강도에 관한 실험평가)

  • Lee, Woo-Jin;Yoon, Seung-Joe;Kim, Seong-Soo
    • Journal of the Korea Concrete Institute
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    • v.15 no.5
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    • pp.689-696
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    • 2003
  • Recently, Appendix A of ACI 318∼02 Code introduced the Strut-and-Tie Model(STM) procedure in shear design of deep flexural members. The STM procedure is widely used in the design of concrete regions where the distribution of longitudinal strains is significantly nonlinear, such as deep beams, beams with large openings, corbels, and dapped-end beams. Experimental study included five high-strength reinforced concrete deep beams with different detailing schemes for the horizontal and vertical reinforcement. The specimens were designed as simply supported beams subjected to concentrated loads on the top face and supported on the bottom face. At failure, all specimen exhibited primary diagonal crack running from the support region to the point load. Specimens which had mechanical anchorages(terminators) gives better representation of the load-carrying mechanism than the specimen had standard 90-degree anchorage at failure in deep flexural members. Based on the test results, shear design procedures contained in the ACI 318-99 Code, Appendix A of the ACI 318-02 Code, CSA A23.3-94 Code and CIRIA Guide-2 were evaluated. The Shear design of ACI 318-99 Code, Appendix A of the ACI 318-02 Code and CIRIA Guide-2 shown to be conservative predictions from 10% to 36% in the shear strength of the single-span deep beam which was tested. ACI 318-99 Code was the lowest standard deviation.

Evaluation on Durability of High Performance Concrete with Expansive Additive and Shrinkage Reducing Admixture (팽창재와 수축저감제를 사용한 고성능 콘크리트의 내구성 평가)

  • Koh, Kyung-Taek;Kang, Su-Tae;Park, Jung-Jun;Ryu, Gum-Sung
    • Journal of the Korea Concrete Institute
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    • v.18 no.2 s.92
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    • pp.205-211
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    • 2006
  • The objective of this study was to evaluate the durability of low shrinkage high performance concrete(LSHPC), which was combined with expansive additives and shrinkage reducing admixtures. We tested for not only LSHPC but also high performance concrete(HPC) and normal concrete(NC) to be compared with the durability of LSHPC. HPC was made in the same water-binder ratio of LSHPC without expansive additives and shrinkage reducing admixture. As a result, it was found that LSHPC had higher compressive and tensile strength than that of HPC. LSHPC showed more excellent performance than HPC and NC in the case of resistance to chloride ion penetration and resistance to carbonation and also showed nearly 100 durability factor in the freeze-thawing test with 500 cycles. From the examination about the watertightness and the pore distribution, it was found that the durability of LSHPC was improved because its hardened cement paste is organized closer. So we can conclude that when LSHPC is applied to structures in field, it is possible to reduce the shrinkage and crack in concrete and improve the durability.

Experimental Study on Flexural Behavior of PSC I Girder and the Effect of External Prestressing (PSC I합성 거더의 휨 거동 및 외부 강선 보강효과에 관한 실험 연구)

  • Lee, Byeong-Ju;Park, Jae-Guen;Kim, Moon-Young;Shin, Hyun-Mock;Park, Chang-Ho
    • Journal of the Korea Concrete Institute
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    • v.19 no.6
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    • pp.755-762
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    • 2007
  • For the evaluation of the load carrying capacity of the deteriorated PSC I girder bridge in service load state and the verification of the grade to the reinforcement effect of actual bridge strengthened by external prestressing tendons, the field test using vehicles is applied widely. Because this teat was executed in elastic range, the investigation of the characteristics of behavior caused by live load is only available. And it is impossible to estimate load carrying capacity in limit state and nonlinear behavior after that a crack is appeared. In this study, the 27-year-old prestressed concrete girder bridge is used and various load tests are performed, so we evaluate the behavior characteristics of the bridge in service load state and ultimate load state, and estimate the load carrying capacity of bridge. In addition, the artificial damages are induced from cutting internal tendons, and external tendons is added to strengthen it as much as vanished internal tendons. Next we compare the damage state with the strengthening state. In case of the application of external prestressing method to PSC I girder bridge, the present experiment result may decide more exactly the load carrying capacity of actual bridge, the amount for reinforcement, and the standard of quality control etc. at reinforcement work.

Early Age Behavior of Thin Bonded Continuously Reinforced Concrete Overlay on Aged Jointed Plain Concrete Pavement (노후 줄눈 콘크리트 포장 보수를 위한 얇은 연속 철근 콘크리트 덧씌우기 포장의 초기거동 평가)

  • Ryu, Sung-Woo;Nam, Jung-Hee;Kim, Ki-Heun;Cho, Yoon-Ho
    • International Journal of Highway Engineering
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    • v.11 no.2
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    • pp.121-132
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    • 2009
  • Thin bonded continuously reinforced concrete overlay(CRCO) was constructed on He existing jointed plain concrete pavement(HCP) surface at Seo-Hae-Ahn express highway in South Korea in order to evaluate its applicability and performance. Two sections of road were considered for this evaluation. In the first section, the concrete overlayer was placed and cut down to the existing layer to form transverse joints while CRCO was constructed on top of the existing layer in the second section. Early strength concrete(Type III) was utilized for both overlay sections. The depth of milling and the thickness of overlaid layer were 5 cm and 10 cm, respectively. Several vibrating wire gauges(VWG) were installed to evaluate the performance of CRCO with respect to curling, delamination, and crack propagation. As a result of the strength test, it was found that strength of the material reaches the design criteria within 1-3 days. Analysis with vibrating wire gauge(VWG) showed CRCO effectively restricts joint movement. High adhesive strength also was observed from the material regardless of length of aging. Meanwhile, transverse cracks were observed on the middle of the section where JPCP overlay was applied whereas arbitrarily cracks in transverse direction were observed on the section where CRCP was applied.

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Evaluation on Mechanical Properties of Organic of Fiber Reinforced Concrete Using Macro Forta Fiber (매크로 포타 섬유를 사용한 섬유 보강 콘크리트의 역학적 특성 평가)

  • Ryu, Hwa-Sung;Kim, Deuck-Mo;Shin, Sang-Heon;Ryu, Il-Hwan;Joe, Ji-Min
    • Journal of the Korea Institute of Building Construction
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    • v.17 no.4
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    • pp.321-329
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    • 2017
  • Concrete is a semi-brittle material, so its compressive strength is high but its tensile strength is low. The use of fiber-reinforced concrete to improve the disadvantages of such concrete can be an effective way to toughen effective toughness, and the performance is improved by using steel fiber reinforced concrete for structures that are vulnerable to bending forces. However, alternative materials are required due to corrosion of steel fiber and lowering of workability. The purpose of this study is to evaluate the availability of replacing steel fiber reinforced concrete by evaluating physical properties, mechanical properties and drying shrinkage properties of concrete using macro forta fiber with excellent diffusibility. Experimental results show that the macro forta fiber has better fluidity and mechanical performance than the steel fiber reinforced concrete. It was also confirmed that the crack resistance of concrete using Macro Forta fiber is effective in improving structural cracking and drying shrinkage resistance compared to steel fiber reinforced concrete.