• Tunnel and Underground Space
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• v.10 no.3
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• pp.316-319
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• 2000

Stress variation due to size variation and the eccentricity of ring type tensile specimen was analyzed by FLAC program. To get the stable tensile strength the ratio of inner to outer ring diameter should be within a certain range. Diameter ratio of 0.3 was suggested to be adequate. It seemed to be difficult to determine the tensile strength because of stress distortion if eccentricity exceeded some limit. To limit the error in 10%, lateral and axial eccentricity was analyzed to be in the limits of 3% and 10%, respectively.

• Magazine of korean Tunnelling and Underground Space Association
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• v.13 no.2
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• pp.41-49
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• 2011

양북터널은 굴착과 동시에 라이닝콘크리트를 타설하였다. 터널굴착과 라이닝콘크리트의 동시시공을 위한 적정시공 Cycle을 결정하고, 이에 따른 양생기간과 양생온도를 설정하는 순으로 시험하였다. 라이닝콘크리트는 품질관리를 위해 보온장치를 탑재한 Sliding form과 양생대차를 운영하고, 균열을 최소화하기 위해 양생온도와 양생시간 및 탈형강도 등을 시험에 의해 결정하였다. 시험과정은 터널내부와 라이닝콘크리트 내부온도를 계절별로 측정하고, 양생온도별로 콘크리트의 강도를 측정하였다. 거푸집 탈형시 콘크리트 온도가 터널내부의 온도로 수렴하기까지는 $15{\sim}20^{\circ}C$의 차이로 측정되었고, 거푸집 탈형을 위한 콘크리트 초기강도 4MPa을 발현하는데는 양생온도에 따라 차이가 발생하지만 시공 Cycle에 적합한 양생시간은 약 20시간이고, 이 때의 양생온도는 $23^{\circ}C$ 이상이었다. 위의 시험결과대로 현장에서 라이닝콘크리트를 양생한 결과 시공 Cycle과 압축강도 및 콘크리트면의 외관 등이 만족한 결과를 나타내었다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.2
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• pp.111-118
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• 2020

In this paper, the flexural creep behavior of hooked-end steel fiber reinforced high-strength concrete was evaluated to investigate the steel fiber content influence on long-term behavior of flexural members. An experimental program consisted of nine prismatic beam specimens with dimensions of 150 × 150 × 600mm reinforced with different contents of steel fiber (0, 0.75 and 1.5% at the volume fraction). To introduce flexural creep loading to notched prismatic beam specimens, a four-point bending test setup was used. The sustained load with 40% of the flexural strength was applied by means of a lever system and controlled by a load cell for 90 days. During sustained loading, crack mouth opening displacement (CMOD) was monitored. Conventional flexural test after creep tests were carried out to evaluate the residual capacity of each specimen. Test results showed that steel fiber content has a significant effect on the flexural creep behavior of high-strength concrete and long-term flexural load with 40% of flexural strength doesn't generate negative effects on the residual capacity of steel fiber reinforced high-strength concrete.

• Journal of the Korea Institute of Building Construction
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• v.23 no.5
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• pp.537-546
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• 2023

For the purpose of fire delineation within buildings, steel walls in Korea are mandated to undergo rigorous certification as fire-resistant entities, substantiated via a series of qualitative assessments. Predominantly, these evaluations comprise the fire resistance test paired with supplementary examinations; specifically for steel walls, these encompass the gas hazard and panel bending strength tests. Given the prevalence of semi-noncombustible core materials, gas hazard tests are largely rendered superfluous, pivoting the focus solely onto the panel bending strength test during the certification trajectory. This particular test is designed to gauge the flexural robustness of individual wall panels. An enhanced bending strength is postulated to fortify both the structural integrity and thermal insulation of the wall by mitigating potential deformations. In this scholarly exploration, an analytical deep dive was undertaken into extant, valid certification test datasets. The endeavor aimed to ascertain the depth of correlation between the designated fire resistance metric and the bending strength, the latter being the sole supplementary assessment for steel walls. In distilling the findings, it was discerned that temperature elevations beyond baseline values exhibited no statistically salient linkage with the panel's bending strength.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.2
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• pp.98-104
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• 2018

Nondestructive strength Equations are commonly used to determine the strength of concrete. However, the application of the existing equations may include many errors because this method is proposed on the basis of limited experimental parameters while actual bridges have various parameters such as conditions of concrete mixtures, properties of concrete strength, etc. Also, the error among the existing equations causes the confusion when engineers select the proper estimation equation for the concerned bridge. In this study, a series of the field inspection and the test have been performed on 297 existing bridges, in order to evaluate the bridges, based on the test results of the in-depth inspection, and the estimated strengths by means of the nondestructive strength equations are analyzed and compared with results of the core specimen strengths. According to results of analyses, the nondestructive strength equation proposed by CNDT Committee of Architectural Institute of Japan had high relationship with core strength. However, the strengths predicted by this equation, are underestimated when concrete's strengths are over 30 MPa, otherwise, they are overestimated. Also in this paper, based on the relationship between the estimated nondestructive concrete strengths and the core specimen strengths the modified strength equation through simple correlation analysis is proposed.

• Cement
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• s.12
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• pp.53-72
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• 1965

• International Journal of Highway Engineering
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• v.13 no.2
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• pp.159-166
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• 2011

This research was performed to evaluate physical properties of polysulfide epoxy overlay material for bridge deck as part of a review for possibility of domestic application of polymer concrete for bridge deck pavement. In order to evaluate strength characteristics, compressive strength, flexural strength and bond strength were tested, and, for durability characteristics, chloride ion penetration resistance and freeze/thaw resistance were tested along with ultraviolet rays impact evaluation. The tests showed that the results met the criteria suggested by the American Concrete Institute in terms of compressive strength, flexural strength and bond strength. However, in terms of the strengths measured at various test temperatures, it was found that the epoxy material was highly dependent on temperature, and, therefore, this should be considered at the time of domestic application of the epoxy material later. Deflection characteristics was checked through flexural strength test and it was found that bridge deck pavement using the epoxy material was excellent compared to bridge deck pavement using asphalt. Furthermore, the results of chloride ion penetration resistance test and freeze/thaw resistance test were also excellent. In the evaluation of ultraviolet rays impact on epoxy slurry mixture, reduction of strain was noticed with increased strength, but the deflection characteristics after exposure to ultraviolet rays was better than the existing acryl polymer concrete. Therefore, it is concluded from the research that the polysulfide epoxy overlay material has the physical properties that are appropriate to pavement of bridge deck.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.8
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• pp.32-36
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• 2018

A tensile test evaluation of a polypropylene plate was carried out using an Instron tester with a capacity of 500 kgf. To evaluate the strain rate sensitivity of the polypropylene plate with a thickness of 0.8 mm, a tensile test was performed at room temperature through strain rate variations from $5{\times}10^{-4}/sec$ to $5{\times}10^{-2}/sec$. From these, the changes in strength due to the strain rate change and temperature change were compared. As a result of the experiment, the strength increased with increasing initial strain rate. Polypropylene was found to be a material with a positive strain rate sensitivity. In addition, the high temperature tensile properties of the polypropylene plate were evaluated using high temperature tensile tests at 80, 120, and $160^{\circ}C$. The strength decreased with increasing temperature. In particular at $160^{\circ}C$, the tensile strength decreased to zero. The increase in yield strength and the tensile strength at room temperature, $80^{\circ}C$ and $120^{\circ}C$ were similar. At $160^{\circ}C$, however, there was almost no increase in strength because the stress approached zero. In the high temperature tensile test, the tensile strength increased more than the increase in yield strength with increasing strain rate.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.2
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• pp.632-637
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• 2021

In order to develop future construction technology, research is actively being conducted on concrete construction technology using 3D printing, which is currently in the spotlight as a future industry in domestic and foreign construction industries and academia. However, 3D printing technology is currently being developed and does not meet the requirements for proper construction technology and the properties of concrete materials, and it is difficult to apply in the actual field. Research is also needed for the durability management and maintenance of constructed structures. This work compares the compressive and flexural strength to that produced in conventional molds by dividing the 3D printed concrete output by the laminated X, Y, and Z axes. The compressive strength of a test specimen in the II Z-axis test direction was 8-10% higher than that of the other test directions (I and III Y axes and X axis). The strength was 4% lower than that of a molded test specimen. As of 28th of the age, the bending strength of the test specimen in the Z-axis direction was 5 to 7% higher than that of the I and III Y, and X-axis test directions, and the strength was 2% lower than that of the molded test specimen.

• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.2
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• pp.173-180
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• 2005

Metakaolin is a cementitious material for producing high-strength concrete. This material is now used as substitute for silica-fume. In this paper, we did the mechanical and durability test such as compressive/tensile/flexural strength test, chloride ion diffusion, chemical attack and repeated freezing and thawing, carbonation test. In the mechanical tests, 10~15% for binder is optimum substitute rate. And, in the chloride ion diffusion test, according to the increase of substitute of metakaolin & silica-fume for binder, the diffusion coefficient was more reduced. In the chemical attack test, by the filler effect of fine powder such metakaolin and silica-fume, the resistance is more excellent than normal concrete. In the other durability test, the concrete using metakaolin also compared with those of silica-fume substitute concrete. Through these tests, we recognized that metakaolin can be used as a substitute for silica-fume.