• Journal of the Korean GEO-environmental Society
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• v.14 no.6
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• pp.31-38
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• 2013

This study carried out fundamental study on the forest road pavement method of cementing the ground using the compaction equipment after laying by mixing with eco-friendly stabilizer, natural soil and water. Target strength of pavement was set to 2.0MPa and the specimen was produced per mixing ratio of cement, kinds of natural soil and curing period to evaluate the durability and unconfined compressive strength. Unconfined compressive strength test was conducted to compare strength by producing the test specimen mixing environment-friendly cement as well as the test specimen mixing cement with the same mixing ratio. To evaluate the durability, surface abrasion test and water flow resistance test were conducted. In addition, SB and GB tests were conducted using iron marble and golf ball to evaluate the walking satisfaction since it can be used by visitors due to the feature of forest road.

• Tunnel and Underground Space
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• v.21 no.1
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• pp.41-49
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• 2011

This study is to estimate the uniaxal compressive strength (UCS) for the weak rocks using needle penetrometer test. The appropriate ratio of the artificial rocks for this test was cement (C):bentonite (B):water (W) = 1.3:0.7:2.3 or 1.5:0.5:2.0. From the relationship between needle penetration resistance (NPR) measured by needle penetrometer test and an estimated UCS, NPR and UCS tended to increase with increasing the curing period. Also from the relationship between the measured NPR and the measured UCS, NPR-UCS was linearly increased with the curing periods of 3-day to 14-day regardless of the ratio, then in the curing periods of 14-day to 28-day it was nearly constant. In conclusion, the overall relationship between NPR and UCS shows a linear relation for the most part, it means that UCS is possible to be estimated from NPR by needle penetrometer test in the case of weak rocks.

• Journal of the Korea Concrete Institute
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• v.13 no.5
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• pp.507-515
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• 2001

Significant improvements in bond strength between new and existing concrete can be achieved through the modification of the new concrete by latex. This study focuses on the investigation of bond strength of latex modified concrete. Pull-out bond test and uniaxial direct tensile bond test are adopted for evaluating the adhesion characteristics of latex modified concrete to conventional concrete substrate. The main experimental variables are test methods, latex-cement ratio, surface preparations and moisture levels. The results are as follows; The increase of latex-cement ratio substantially improves the adhesion between latex modified concrete and substrate. The effects of surface preparation at substrate into the bonding of latex modified concrete are quite different according to the conditions of surfaces. Thus, an adequate surface preparations are essential for good bond strength. Because the moisture level of the substrate may be critical to achieving bond, optimum moisture condition for a conventional concrete has evaluated in this study. The saturated condition of surface is the most appropriate moisture level among the considered, followed by dry condition and wet condition.

• Journal of the Korean GEO-environmental Society
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• v.13 no.4
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• pp.53-59
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• 2012

In this study, strength and durability of a geo-polymer grout material(HIT) was investigated through unconfined compression strength tests(UCS)), scanning electron microscope(SEM), elution tests, and surface observations. UCS tests showed high initial strength and rapid continuous strength increments when compared to labile wasser glass(LW) and space grouting rocket system (SGR) grout materials, which showed strength reduction after 28 days. The higher strength was also reflected in SEM results which showed calcium silicate hydroxide(C-S-H) gels of the dense hydrate range, indicating higher strength and durability. Additionally, elution tests and grout surface observations showed HIT was in good condition and the decrease in weight was minor when under water for six months. LW and SGR showed the grout surface to be constricted and lower durability due to higher weight increase. These results and observations show HIT to be better suited for coastal structural applications than LW and SGR in long terms of strength and durability.

• Journal of the Korean Society of Hazard Mitigation
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• v.4 no.3 s.14
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• pp.25-31
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• 2004

Rail road slope can be fatted because of existence of unexpected soft subsoil. Purpose of this study is verifying the cause of rail road slope failure and determination of soil strength for remedy. Drilling some boreholes, cone penetration test and field vane test were executed in order to find out the cause of slope failure. In addition, laboratory test was conducted in order to determine soil strength of soft soil sampled as undisturbed state. As a result of both the in-situ and the laboratory tests, the cause of slope failure is thought to be propagation of failure zone by progressive rupture of overconsolidated clay Soft soil strength was determined through back analysis of the failed slope.

• Geotechnical Engineering
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• v.9 no.2
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• pp.27-40
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• 1993

This paper proposes a new procedure carrying out a series of consolidated-undrained triaxial tests with a specimen. In this procedure high confining pressure applied to the specimen keeps constant during the test and each stage of consolidation can be controlled by partial drainage. With this procedure the test time is remarkably reduced by performing a series of triaxial tests with a single specimen. In order to verify the appliesbility of the procedure, standard triaxial compression tests and conventional multi -stage triaxial testy are performed for both undisturbed and disturbed samples and the results are compared with those of the proposed procedure. The comparison shows that strength parameters determined by the proposed procedure are well agreed with those of the other tests and thus it can be said that the procedure is very effective and practical in determining strength parameters.

• International Journal of Highway Engineering
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• v.4 no.4 s.14
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• pp.13-21
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• 2002

This study examines the importance of conditioning temperature and period before measuring fundamental properties of asphalt mixture. Marshall specimens were made and cured in the air for one day and conditioned by submerging at $60^{\circ}C$ water for 30 min before loading. It was observed that if the specimen was cured in a lower (or higher) than normal lab temperature ($25^{\circ}C$) before submerging, the measured values were not consistent. Indirect tensile strength (ITS) was also measured on the specimens cured at different temperatures. Although there is no regulation specifying how long the specimen should be conditioned before testing, it is recommended that the conditioning time be for the specimen to be at $25^{\circ}C$. Test must be conducted for the specimen cured well before conditioning for desired test. If curing temperature was lower or higher than normal, and mixture was not properly cured, then test results would not be reliable. This study showed how long the specimen should be submerged at $60^{\circ}C$ for Marshall test and conditioned at $25^{\circ}C$ for ITS test for the specimens cured in different temperature.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.56.2-56.2
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• 2011

최근 철강, 알루미늄, 이종재료의 접합 등 용접이 어려운 부분에 구조용 접착제의 적용이 증가하고 있는 추세이다. 이를 위해 변성 에폭시레진을 활용한 고접합 강도, 고인성의 구조용 접착제가 연구되어 지고 있다. 피착제의 표면처리는 접합부의 접합강도를 향상시키는 방법으로 알려져 있으나 최근의 구조용 접착제는 표면 전처리 없이도 우수한 접착 특성을 보이는 것으로 기대되고 있다. 본 연구에서는 변성레진에 대해서 각종 표면처리가 접합부 특성에 미치는 영향을 조사하였다. 피착제로는 자동차용 냉연강판인 SPRC440을 사용하였고, 전처리로는 무처리 상태, SiC연마지를 이용한 연마, 아르곤 및 산소가스를 이용한 마이크로웨이브 플라즈마 표면처리, 산세 등의 표면처리를 실시하였다. 에폭시 접착제는 변성 에폭시 레진과 경화제 및 촉매제를 이용하여 직접 포뮬레이션하였다. 단일 겹치기 전단강도 시험과 T-Peel 시험은 각각 ASTM D 1002 규격에 따라 준비하였으며 인장 시험 후 파면은 SEM으로 관찰하였다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.4
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• pp.667-674
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• 1992

Recently advantages in composite and light weight material technique have led to the increased use of structural adhesives in various industries. In spite of such wide application of the adhesive joints, the evaluation method of fracture strength and design methodology of them, have not been established. In this study finite element method, theoretical and experimental analyses were investigated according to changes of lap length and adhesive for adhesive single-lap joint. As the results, the strength evaluation of adhesive joint by conventional nominal stress, was pointed out inadequate strength evaluation and design method regardless stress singularity, stress distribution and crack propagation in its adhesive layer. Also, it was examined the problems to apply fracture mechanics by means of static and fatigue test.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.4
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• pp.585-593
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• 2021

This study investigates the compressive strength of high-strength cement composites with 64 mixture designs and 2 curing conditions. The cement composites were designed with varying water-to-binder ratios, silica fume content to cement, and binder content per unit volume of cement composite to explore compressive strength development depending on its mix design. An increase in the water-to-binder ratio decreased the compressive strength of the composites, having consistency with the trend in normal concrete. The compressive strength increased with ages at an ambient curing temperature, but it was not identified at high-temperature curing. The compressive strength development was negligible in case that silica fume content to OPC is 15%~25%, but a decrease in the con ten t below 15% reduced compressive stren gth. It was more obvious in the specimen of low water-to-binder ratio. The specimen with 840kg/m³ of binder content per unit volume had the highest compressive strength in this study, and the decrease in binder content reduced the compressive strength of high strength cement composites in low silica fume content.