• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.4
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• pp.111-119
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• 2016

Rebound hammer test, SonReb method and concrete core test are most useful testing methods for estimate the concrete compressive strength of deteriorated concrete structures. But the accuracy of the NDE results on the existing structures could be reduced by the effects of the uncertainty of nondestructive test methods, material effects by aging and carbonation, and mechanical damage by drilling of core. In this study, empirical procedure for verifying the in-situ compressive strength of concrete is suggested through the probabilistic analysis on the 268 data of rebound and ultra-pulse velocity and core strengths obtained from 106 bridges. To enhance the accuracy of predicted concrete strength, the coefficients of core strength, and surface hardness caused by ageing or carbonation was adopted. From the results, the proposed equation by KISTEC and the estimation procedures proposed by authors is reliable than previously suggested equation and correction coefficient.

• Korean Journal of Materials Research
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• v.5 no.2
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• pp.191-196
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• 1995

Self-bonding strength developed at the interface of amorphous PEEK films is highly sensitive to the processing variables(time, temperature, and pressure) during the bonding process. In order to examine the effects of these processing variables, amorphous PEEK films were bonded at various bonding conditions and the resultant interfacial bond strengths were measured using a modified single lap-shear test. Experimental results showed that the developed self-bonding strength increases with increase in bonding temperature and is directly proportional to the bonding time raised to the 1/4 power. The applied pressure seems only to produce better wetting at the beginning stage of the bonding process. Conclusively, the self-bonding of amorphous PEEK films provides a great potential for developing excellent bond strength approaching the strength of the parent material without any adhesives in structural applications.

• The Journal of Engineering Geology
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• v.18 no.2
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• pp.227-232
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• 2008

In this study, the pull out resistance characteristics of an anchor bar to support a spillway installed in a slope are investigated by field tests. The injection materials were a cement mortar and cement milk. Unconfined compression strengths of those materials under several conditions were measured. As the result of compression test, the unconfined compression strengths of the cement mortar and the cement milk have positive proportional relation-ship with the water-cement ratio. They also have negative proportional relationship with increasing the curing time. In the same condition of water-cement ratio and curing time, the unconfined compression strength of cement milk is larger than that of cement mortar. In order to reduce the eccentricity in anchor bar during pull-out test in the field, the installation apparatus was improved by inserting a nut type of steel fixing coupling into the anchor bar. As the result of the pull-out test, the strength modification of cement milk was increased steeply at the early curing time. However, that of cement mortar was increased gradually with passing the curing time. Therefore, the cement milk has to use as the injection material for a prompt construction of anchor bar because the strength modification of cement milk is occurred at the early curing time.

• International Journal of Highway Engineering
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• v.5 no.4 s.18
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• pp.37-47
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• 2003

Song-E(scoria) is civil material that we frequently meet with in road building in Jeju-island. It is known that Song-E is the material of high crush and large particle. But, the study on the scoria is not enough, so there are many difficult in handling method. In this study, We research basic strength characteristics on Song-E gathered at various part in Jeju-island. Results of this study(strength characteristics of Song-E) are applied to design of road, breast wall and slope as basic data.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.405-408
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• 2008

The most effective factors that improve sections and elongate spans of the prestressed concrete girders are shapes of sections and strengths of concretes, and the concrete strength is more influenced to enhance the allowable tensile strength on top and bottom fibers than increasing of flexural strength of girders. In this study, 60 MPa high-strength prestressed concretes were constructed at the Wonsoo Bridge where in the 1st section of expanding constructions of the Nonsan to Junjoo Expressway, the high-strength concrete was placed on the eight- 35 meters simple span IPC girders of four lanes of Nonsan direction. During casting of girder concretes, quality controls were carried out with continuing controls of surface moistures and corrections of the unit water using the air-meter methods right after batching. It was confirmed that compressive strengths of girder concretes ensure the target strength and the heat of hydrations of girder concrete were measured. Though using same materials and constructing methods, there're a wide range of strengths of each girder, so, when high-strength concretes cast in the place hereafter, a countermove should be prepared.

• Magazine of the Korea Concrete Institute
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• v.10 no.1
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• pp.119-124
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• 1998

콘크리트는 시멘트, 잔골재 및 굵은 골재, 물 및 첨가제의 양이나 투입순서 ,혼합방법등 여러 가지 요인에 따라 성질이 바뀌게 되는 복합재료이다. 따라서 넓은 의미에서 품질 판정의 한 수단이 되는 콘크리트의 설계기준강도 또는 압축강도 fc'(=28일 압축강도)는 물론 기타의 성질도 정확한 예측이 불가능하다. 즉 소요강도를 목표로 배합된 공시체의 시험결과는 예외없이 통계적 가변성을 나타낸다. 여기에서는 공시체의 7일 강도의 평균치 및 표준 편차와 공시체의 28일 강도 측정치로부터 콘크리트의 압축강도를 추정하는식을 제안하였다. 이를 위하여 7,320개의 강도시험자료를 수집한 후 이들을 선형 회귀 분석법으로 처리하였다. 제안된 식에 의한 콘크리트의 압축강도는 타 추정식에 의한 값보다 실측치에 좀 더 근접함을 보여주었다. 또한 제안식의 검정을 위해 서울지역 자료 5,200개를 수집하여 제안식과 JIS, Slater식과의 오차를 비교한 결과에 따르면 제안식이 더 안전측임을 알 수 있었다. 그리고 슈미트 햄머에 의한 현장 실측 강도와 제안식과의 콘크리트 강도 오차는 대체로 2.3%이었다.

• International Journal of Highway Engineering
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• v.11 no.2
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• pp.67-74
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• 2009

The strength of concrete is one of the most important parameters in evaluating the properties of concrete. Compressive strength of concrete has been widely used because of its convenience of experiments and generality. Compressive strength of concrete varies according to materials and curing conditions. Even with the same materials, the strength varies according to the curing conditions. Therefore, if we want to know the strength of concrete from the construction field, we have to put it in exactly the same curing condition with the construction field. But it is impossible to make the exactly same curing conditions in the laboratory. Also damages occur in order to measure the strength of concrete, because the core hat to be made into the pavement. To overcome these limits, many studies of nondestructive method have already been researched. It was already proven that shear wave velocity was very closely related to the compressive strength. In this study, three different curing temperatures with the same mixture paste were used, and compressive strength and shear wave velocity, according to the aging were measured. The relationship between these two parameters was examined. As results, curing temperature affected the compressive strength and the shear wave velocity, but did not affect the relation between them.

• Journal of the Society of Disaster Information
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• v.7 no.1
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• pp.43-50
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• 2011

The Application of Steel Fiber Shotcrete in tunneling construction has become part of tunneling practice at least since the 1970s because of its high bending and tensile properties. Over the past 3 decades, researcher from all over the world have been significantly developing the associated technologies for improved performance of SFRS. But still it has some major drawbacks in terms of durability, damage of pumping hose, wastage due to rebound concrete, corrosion and it costs high. To overcome this situation researcher has to look for some alternative material. Therefore, this part study deals with the three types of fiber in order to find good alternative for steel fiber. Polyamide and Polypropylene fiber were used in this study with 0.6, 0.5% mixing ratio. To evaluate its fresh and harden properties air content, slump, compressive, split tensile and bending strength were measured. After comparing the results of all three types of fiber reinforced concrete with its different mixing proportion this study propose that polyamide fiber with addition ratio of 0.6 % for field use.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.4
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• pp.349-357
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• 2019

Controlled low strength material(CLSM) has been developed using variety of material such as excavated soil, industrial by-product and industrial waste. But theses research limited at laboratory test and failed at commercialization. So in this paper evaluates CLSM used excavated soil characteristics such as flowability, bleeding rate, early strength for following process and 28day strength for re-excavatability. Also, various mix proportion of CLSM by water-binder ratio and soil-binder ratio were evaluated in laboratory. And derive the optimized CLSM mix proportion for using at field application test by movable batch plant. After applying CLSM at trench, evaluate core sample strength and excavatability by shovel, pickax and excavator for verify re-excavation. Furthermore, measure the level change after casting CLSM to inspect subsidence stability. As results of these assessments, not only confirmed the characteristics of CLSM at field but the fillability around pipe and subsidence stability.

• Journal of the Korean Geosynthetics Society
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• v.8 no.4
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• pp.27-34
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• 2009

In this paper, characteristics of shear strength and deformation of geosynthetics-reinforced slag materials are described. In order to investigate the effect of geosynthetics on shear strength and deformation behavior of slags, when they are reinforced with geosynthetics or geomat such as PET mat, large triaxial tests were performed under consolidated-drained condition. The materials used in the study are real ones as they are in the field, so that the scale effect of samples disappeared. From the large triaxial tests, it was observed that the stress-strain relationship of geosynthetics-reinforced slags shows relatively small dilatancy and weak tendency of strain hardening, compared with that of slags without reinforcement. The shear strength parameters such as apparent cohesion and internal friction angle increase with PET mat reinforcement, consequently result in about 1.2 (for low confining pressure) to 1.4 (for high confining pressure) times of shear strength of un-reinforced sample. Therefore, the adoption of geomat-reinforced slag layers leads to an increase in the factor of safety for embankment design on soft soil formations.