• Journal of the Korea Concrete Institute
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• v.17 no.3 s.87
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• pp.455-464
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• 2005

Today the application of antiwashout underwater concrete to the construction sites is increasing steadily, while its reliability is in issue. Particularly, antiwashout underwater concrete is known to have very weak durability on frost attack, and hence Japan society of civil engineers(JSCE) regulated that not to use of antiwashout underwater concrete where the freezing and thawing is suspected. This study aims the improvement of the freezing and thawing resistance for antiwashout underwater concrete. From the results of fundamental test, FA20 and SG50 showed good performance in fluidity and long term compressive strength than control concrete. Meanwhile, MK10 marked the highest compressive strength through the whole curing age but a defect on fluidity was discovered. The results from the repeated freezing and thawing test show that the large volumes of air entrapped by cellulose based antiwashout underwater admixture gave bad effects to frost durability and hence not much benefits were confirmed from the use of mineral admixtures. However there were some increasing effects on frost durability of MK10 and SG50 by securing $6{\pm}0.5\%$ of entraining air. In the meantime, there was a increasing tendency of frost durability by increasing blame's fineness of ground granulated blast furnace slag.

• International Journal of Highway Engineering
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• v.11 no.3
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• pp.41-49
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• 2009

Cement concrete pavement has become more common in Korean highway systems. However, as its service period increases, there are some technical problems occurs and no clear solution is available primarily due to the lack of active researches. This research, hence, aims to develop a new mix proportion that may provide better strength and durability with extended service life. Based on a variety of literature reviews, the experimental variables were determined as unit cement content, S/a ratio and W/C ratio. From the experimental works, it is recommended to increase the unit cement content up to 375kg/$m^3$, 400kg/$m^3$ and 425kg/$m^3$. The target slump and air content were set 40mm and 5%, respectively. The maximum size of coarse aggregate was decided to be 25mm because of the easiness of supply in the field. The reduction of W/C ratio was necessarily required and decreased to 0.4 which was proven not to cause any mixing problem with the increased unit cement contents along with polycarbon-based high range water reducing agent. In addition, it was known that the S/a ratio could be reduced to 0.34. The lowered S/a might be possible because of the increased cement paste and hence increased cohesiveness and workability.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.2
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• pp.283-299
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• 2017

The leakage of tunnel causes the long-term durability of the structures such as concrete lining to deteriorate. The cause of durability degradation can be various substances contained in groundwater such as chloride, sulphate, water, and gas. In this study, a series of test were carried out to determine the watertightness performance and the resistance to salt water of the spray-applied membrane used as non-structural rock support or as a waterproof material for tunnels. As a result, it was found that the penetration of water could occur in a specimen, and the reason was that the internal pores generated by the mixing of the liquid polymer and the powder material and the internal pores were connected by the water pressure. The tensile strength of the test specimens immersed in distilled water and saline water was found to be reduced to less than half of the tensile strength in normal condition. In addition, The elongation was measured to be higher in distilled water than in salt water. However, this result will require further investigation.

• Journal of the Korean Geosynthetics Society
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• v.17 no.4
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• pp.169-177
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• 2018

Glass fiber reinforced polyester (GFRP) composites are widely used as structural materials in harsh environment such as underground pipes, tanks and boat hulls, which requires long-term water resistance. Especially, these materials might be damaged due to delamination between gelcoat and composites through an osmotic process when they are immersed in water. In this study, GFRP laminates were prepared by surface treatment of UPE (unsaturated polyester) gelcoat by vacuum infusion process to improve the durability of composite materials used in underground pipes. The composite surface coated with gelcoat was examined for surface defects, cracking, and hardness change characteristics in water-immersion environments (different temperatures of $60^{\circ}C$, $75^{\circ}C$, and $85^{\circ}C$). The penetration depth of cracks was investigated by micro CT imaging according to water immersion temperature. It was confirmed that cracks developed into the composites material at $75^{\circ}C$ and $85^{\circ}C$ causing loss of durability of the materials. The point at which the initial crack initiated was defined as the failure time and the life expectancy at $23^{\circ}C$ was measured using the Arrhenius equation. The results from this study is expected to be applied to reliability evaluation of various industrial fields where gelcoat is applied such as civil engineering, construction, and marine industry.

• Journal of the Korea Concrete Institute
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• v.16 no.4 s.82
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• pp.521-528
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• 2004

In general, polymer concrete has more excellent mechanical properties and durability than Portland cement concrete, but very sensitive to heat and has large deformations. In this study, the long-term creep behaviors was predicted by the short-term creep test, and then the characteristic of creep of recycled-PET polymer concrete was defined by material and experimental variables. The error in the predicted long-term creep values is less than 5 percent for all polymer concrete systems. The filler carry out an important role to restrict the creep strains of recycled PET Polymer concrete. The creep strain and specific on using the $CaCO_3$ were less than using fly-ash. The creep increases with an increase in the applied stress, but not proportional the rate of stress increase ratio. The creep behavior of polymer concrete using recycled polyester resin is not a linear viscoelastic behavior.

• Journal of Biomedical Engineering Research
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• v.10 no.2
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• pp.117-124
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• 1989

The intelligent trajectory control method that controls moving direction and average velocity for a prosthetic arm is proposed by pattern recognition and force estimations using EMG signals. Also, we propose the real time trajectory planning method which generates continuous accelleration paths using 3 stage linear filters to minimize the impact to human body induced by arm motions and to reduce the muscle fatigue. We use combination of MLP and fuzzy filter for pattern recognition to estimate the direction of a muscle and Hogan`s method for the force estimation. EMG signals are acquired by using a amputation simulator and 2 dimensional joystick motion. The simulation results of proposed prosthetic arm control system using the EMf signals show that the arm is effectively followed the desired trajectory depended on estimated force and direction of muscle movements.

• Magazine of the Korea Concrete Institute
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• v.10 no.5
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• pp.177-187
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• 1998

최근 국내에서 해양 구조물, 장대 교량의 하부구조물, LNG저장탱크 등 매스콘크리트의 증가추세에 따라 구조물의 고내구성과 관련하여 시멘트의수화열에 의한 온도균열의 발생을 최소화 시킬 수 있는 3성분계 혼합형 저발열시멘트가 개발되어 실 구조물의 적용단계에 있으나, 저발열시멘트가 개발되어 실 구조물의 적용단계에 있으나 저발열시멘트의 특성에 대한 전반적인 연구보고가 국내에서는 미진한 실정이다. 따라서 본 연구에서는 3성분계 혼합형 저발열시멘트의 특성 및 코\ulcorner리트의기초물성을 1종 보통포틀랜트 시멘트, 5종 내황산염시멘트, 슬래그시멘트와 비교하였다. 글 결과 저발열 콘크리트의 찹축강도는 초기재령에서 강도발현률이 적은 반면 장기강도발현률은 상당히 큰 경향을 보였다. 또한 수화열은 1종시멘트를 사용한 콘크리트에 비하여 1/3~1/2정도로 매스콘크리트의 수화열을 대폭적으로 저감시킬 수 있을 뿐만 아니라 염소이온에 대한 저항성이 상대적으로 높게 나타나 거대 해양 구조물의 적용에 매우 유리한 시멘트로 판단되었다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.3
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• pp.136-142
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• 2019

Nuclear power plant concrete structures are in contact with the coast, and durability due to chloride attack is very important because it is used as cooling water by taking seawater. For this purpose, a 3-year long-term saltwater immersion test was carried out to evaluate chloride ion diffusion coefficient and age apponent (m) The m values of the foundation with 4,000 class was 0.35 ~ 0.39, similar to KCI or ACI suggested values. essential service water constructions and tunnels of 5,000 class were 0.44 ~ 0.53 and 6,000 class, and 0.62 of reactor containment buildings were similar to the proposed values of FIB. As a result of the prediction of the service life with the measured age coefficient, all the safety related concrete structures of the nuclear power plants satisfied the service life of more than 60 years.

• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.2
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• pp.47-53
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• 2010

Very-early strength latex-modified concrete (VES-LMC) was developed with a focus on workability, strength development and long-term durability that would allow for opening a bridge to traffic only 3 hours after concrete placement, which would be useful when repairing concrete bridge deck overlays. However, even though usage of latex in VES-LMC improves the durability, it has a disadvantage that it produces lots of entrained air. Therefore, specific plan is necessary since it is weak for freezing and thawing in air-void structure. In the present study ultra-fine fly ash (UFFA) was used. Test results are follows ; Air content of VES-LMC UFFA (VES-LMC using UFFA) concrete was decreased since major pozzolan reaction was happened in one day. It was also found that total air content of concrete was decreased with pozzolan reaction since air content in 28 days was the same with one day air content. The addition of calcium hydroxide increased entrained air which is smaller than size of 200 ${\mu}m$. It was effective to improve the air-void structure of VES-LMC since spacing factor can be confirmed as smaller than size of 200 ${\mu}m$ using more than 15% of UFFA.

• Journal of the Korea Institute of Building Construction
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• v.18 no.5
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• pp.455-461
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• 2018

The purpose of this study is to evaluate the tensile strength performance of the polyurethane coating material used as the waterproofing material in concrete structures. A linear regression equation is proposed to establish a correlation on the tensile strength of polyurethane coating membrane against periodic exposure to chemical degradation. The polyurethane film membrane showed a minimum strength of 23% to a maximum of 38% when subjected to chemical degradation. The elongation rate showed a relation with the tensile strength deterioration rate of at least 15% to 22% at maximum, and the proposed regression equation could be used to predict the degree of performance change of the polyurethane coating membrane under chemical degradation condition.