• Advances in concrete construction
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• 제10권3호
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• pp.195-209
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• 2020

This study investigates the behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC) with hybrid macro-micro steel and macro steel-polypropylene (PP) fibers. Compression, direct and indirect tension tests were carried out on cubic and cylindrical, dogbone and prismatic specimens, respectively. Three types of macro steel fibers, i.e., round crimped (RC), crimped (C), and hooked (H) were combined with micro steel (MS) and PP fibers in overall ratios of 2% by volume. Additionally, numerical analyses were performed to validate the test results. Parameters studied included, fracture energy, tensile strength, compressive strength, flexural strength, and residual strength. Tests showed that replacing PP fibers with MS significantly improves all parameters particularly flexural strength (17.38 MPa compared to 37.71 MPa). Additionally, the adopted numerical approach successfully captured the flexural load-deflection response of experimental beams. Lastly, the proposed regression model for the flexural load-deflection curve compared very well with experimental results, as evidenced by its coefficient of correlation (R²) of over 0.90.

• 한국환경과학회지
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• 제10권4호
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• pp.311-314
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• 2001

The asphalt mixture with CRM(Crumb Rubber Modifier) is known to show a better performance in resisting thermal cracking, fatigue cracking and rutting compared with the conventional mixture. The laboratory tests on the physical characteristics of indirect tensile strength, density, flow and Marshall value of the CRM asphalt were conducted. The test results show that CRM asphalt has better physical characteristics than that of conventional asphalts. And the analysis on the noise reduction effect, penetration capacity from the field test on the national road in Haksan of Chungbuk, and recycling of tire waste were conducted. From this study, the results show that 1% CRM asphalt has higher the noise reduction effect and penetration capacity that those of conventional asphalts. And, optimal contents of crumb rubber modifier in the asphalt binder is one percent. In this case, crumb rubber modifier were used 10 kg to make the asphalt binder of one cubic meter. So it was named as Eco-asphalt.

• 한국터널지하공간학회 논문집
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• 제21권4호
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• pp.501-518
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• 2019

심부 지하환경 조건에서 측정된 암석물성의 사용은 고준위폐기물처분장의 장기 안전성 평가 측면에서 해석의 신뢰성을 향상시킬 수 있다. 본 연구는 지하처분연구시설(Korea atomic energy research institute Underground Research Tunnel, KURT)의 화강암(한국원자력연구원, 대전)을 대상으로 고준위폐기물 처분장에서 예상되는 복합환경 조건을 구현한 후 암석의 역학적 물성 변화를 측정하였다. 실험은 심지층 처분환경이 모사되도록 열-수리-역학적 복합 환경(Thermo-Hydro-Mechanical, THM)이 조절될 수 있는 실험장치를 제작하였다. 다양한 복합 실험조건(M, HM, TM, THM)을 구현하여 일축압축강도와 간접인장강도, 탄성계수, 포와송비 등의 암석물성을 측정한 후 그 결과를 분석하였다. 실험결과, 처분장 근계암반 예상 온도범위 내에서는 KURT 화강암의 역학적 물성이 온도의 영향 보다 포화유무에 따른 변화가 더 큰 것을 확인할 수 있었다. 또한, 동일한 온도 조건에서 포화 유무에 따른 일축압축시험 결과는 최대 약 20%의 상대적인 차이를 보였으며, 간접인장시험 결과는 최대 13%의 차이가 발생하였다. 따라서 처분장의 장기거동에 따른 성능평가 및 안전성 예측을 위해서는 기존의 상온 실내시험을 통해 도출된 암석물성을 사용하기보다 심부 지하환경을 반영한 암석의 복합물성을 활용하는 것이 해석의 신뢰도 향상에 기여할 수 있을 것이다.

• 한국도로학회논문집
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• 제16권5호
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• pp.73-82
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• 2014

PURPOSES : The purpose of this study is to determine the optimum addition rate of SBR latex through the evaluation of durability and strength of SBR latex applied soil pavement. Formerly used materials such as fly ash and cement in soil pavement had resulted in decreased durability due to micro crack by heat of hydration and shrinkage crack in winter. However, that agglutinated polymers help adhesion to aggregate increased comes up with preventing the crack opening when the number of capillary tubes of SBR latex get decreased in the hydration process of cement. Therefore, in this study, it is suggested that the evaluation of the field applicability of soil pavement be conducted through the performance lab test in terms of strength increment, adhesion improvement, and crack resistance based on SBR latex addition rate. METHODS : In order to evaluate the field applicability of soil pavement, SBR latex was added 0 to 3% by 1% increment, with fixed cement contents of 3% and 5%. The resistance of shear failure and crack of soil pavement were evaluated by performing the uniaxial compressive strength test and indirect tensile strength test at -20 and $20^{\circ}C$, respectively. RESULTSCONCLUSIONS : It was found out that from both tests, resistance of shear failure and crack were improved with increment of curing time, and especially more than 2% of SBR latex addition rate and 5% cement content gave better results.

• 한국지반공학회논문집
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• 제22권10호
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• pp.139-150
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• 2006

울산분지 퇴적암을 대상으로 Schmidt hammer 타격시험을 시행하여 일축 압축강도, 압열 인장강도, 탄성계수, 흡수율 및 간극율과의 상호 관계를 구명하였다. 기 연구된 결과는 여러 암종이 혼합된 결과로 실용적 적용에 어려움이 있어 지질학적 생성배경의 차이로 인한 원인을 배제하고 실용적 적용에 유용하도록 울산분지 퇴적암만을 대상으로 하여 연구를 시행하였다. Schmidt 햄머 반발지수와 각 실험결과상호간에 높은 상관성이 있으며 본 연구 결과 값으로 상호 교차검정을 한 결과도 만족할 수 있는 결과가 도출되었다.

• Corrosion Science and Technology
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• 제20권1호
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• pp.26-36
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• 2021

Pipes operating in the seawater environment faces cavitation degradation and corrosion of the metallic component, as well as a negative synergistic effect. Cavitation degradation shows the mechanism by which materials deteriorate by causing rapid change of pressure or high-frequency vibration in the solution, and introducing the formation and explosion of bubbles. In order to rate the cavitation resistance of materials, constant conditions have been used. However, while a dynamic cavitation condition can be generated in a real system, there has been little reported on the effect of ultrasonic amplitude on the cavitation resistance and mechanism of composites. In this work, 3 kinds of epoxy coatings were used, and the cavitation resistance of the epoxy coatings was evaluated in 3.5% NaCl at 15 ℃ using an indirect ultrasonic cavitation method. Eleven kinds of mechanical properties were obtained, namely compressive strength, flexural strength and modulus, tensile strength and elongation, Shore D hardness, water absorptivity, impact test, wear test for coating only and pull-off strength for epoxy coating/carbon steel or epoxy coating/rubber/carbon steel. The cavitation erosion mechanism of epoxy coatings was discussed on the basis of the mechanical properties and the effect of ultrasonic amplitude on the degradation of coatings.

• 한국도로학회논문집
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• 제19권2호
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• pp.67-74
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• 2017

PURPOSES : The objective of this study is to ascertain the curing period of cementless cold central plant recycled asphalt base-layer, using mechanical analyses and specimen quality tests on the field. METHODS : Cold central plant recycled asphalt base-layer mixture was produced in the plant from reclaimed asphalt, natural aggregate, filler for the cold mix, and the modified emulsion AP using asphalt mix design and plant mix design. In order to examine the applicability of the curing period during the field test, the international standards for the possibility of core extraction and the degree of compaction and LFWD deflection were analyzed. Moreover, Marshall stability test, porosity test, and indirect tensile strength test were performed on the specimens of asphalt mix and plant mix design. RESULTS : The plant production process and compaction method of cementless cold central plant recycled asphalt base-layer were established, and the applicability of the optical moisture content for producing the mixture was verified through the field test. In addition, it was determined that the core extraction method of the conventional international curing standard was insufficient to ensure performance, and the LFWD test demonstrated that the deflection converges after a two-day curing. However, the back-calculation analysis reveals that a three-day curing is satisfactory, resulting in a general level of performance of dense asphalt base-layer. Moreover, from the result of the specimen quality test of the asphalt mix design and plant mix design according to the curing period, it was determined that the qualities satisfied both domestic and international standards, after a two-day curing. However, it was determined that the strength and stiffness after three-day curing are higher than those after a two-day curing by approximately 3.5 % and 20 %, respectively. CONCLUSIONS:A three-day curing period is proposed for the cementless cold central plant recycled asphalt base-layer; this curing period can be demonstrated to retain the modulus of asphalt-base layer in the field and ensure stable quality characteristics.

• 한국도로학회논문집
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• 제1권2호
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• pp.135-154
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• 1999

Compaction of asphalt pavement is one of the important processes to make good quality one. There are many laboratory-compaction methods to simulate field compaction, including Marshall compaction, Hveem compaction, gyratory compaction, and etc. The most common method used to determine the fundamental properties of asphalt mixture for design is Marshall method which is using impact energy. However, there is major difference between field compaction using kneading compaction and Marshall compaction using impact energy. Therefore, the gyratory compactor, which currently is the best to simulate the field compaction, was employed. The fundamental properties of asphalt specimen compacted by gyratory compactor and Marshall compactor were determined using laboratory test. From the tests, slag mixture with carbon black or pyrolyzed carbon black showed better performances, such as, in low susceptibility to temperature, high resistance against water and rutting, and high resilient modulus and indirect tensile strength.

• Advances in concrete construction
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• 제10권6호
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• pp.489-498
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• 2020

This paper investigates mechanical properties of roller compacted concrete (RCC) involving reclaimed asphalt pavement (RAP). In this way, a set of 276 cylindrical RCC specimens were prepared with different RAP sizes (i.e., fine, coarse & total) at various ratios (i.e., 10%, 20%, and 40%). Results reveal that incorporation of RAP decreases unconfined compressive strength (UCS), modulus of elasticity (E), and indirect tensile (IDT) strength of RCC. For each RAP size, a regression model was used to maximize RAP content while satisfying the UCS lower limit (27.6 Mpa) mentioned by ACI as a minimum requirement for RCC used in pavement construction. Moreover, UCS of RAP incorporated mixes, dissimilar to that of control mixes, was found to be sensitive and insensitive to the testing temperature and curing time after 7 days, respectively. The results also demonstrate that the higher amounts of RAP, the more flexibility in RCC is. This issue was also proved by the results of modulus of elasticity test. In addition, the toughness index (TI) shows that increase in RAP content leads to up to 43% increase in energy absorbance capacity of RCC.

• 한국산학기술학회논문지
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• 제22권3호
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• pp.611-619
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• 2021

다공성 아스팔트 포장은 혼합물 속에 포함된 20%정도의 공극으로 인해 도로의 수막현상을 억제하여 교통사고를 줄이고 교통소음을 획기적으로 줄이는 등 다양한 순기능을 갖는다. 그러나 다공성 아스팔트 혼합물은 혼합물 속에 포함된 20% 정도의 공극 때문에 혼합물의 내구성이 취약하게 되며, 이러한 취약한 내구성이 다공성 포장의 적용을 확장하는데 제약요인이 되고 있다. 본 연구의 목적은 다공성 포장의 내구성을 향상시키기 위해 최대입경, 온도 그리고 공극률의 변화가 혼합물의 균열저항성 및 수분민감성 등 혼합물의 내구성에 미치는 영향을 평가하는 것이다. 다공성 아스팔트 혼합물의 내구성을 평가하기 위해 간접인장강도를 균열저항성 및 수분민감성의 척도로 설정하였다. 공극률이 20%로 동일하고 최대입경이 13mm, 10mm, 8mm인 혼합물에 대하여 상온과 동결융해를 경험한 시료에 대하여 간접인장강도 시험을 실시하였다. 그리고 최대입경 10mm인 동일한 재료로 공극이 20%와 22%인 혼합물에 대하여 동일한 시험을 실시하였다. 실험결과 공극률은 20%로 동일하고 최대입경의 변화와 온도의 변화에 유의한 차이를 보이는 것으로 나타났다. 특히 실험온도에 대해서는 상온과 저온에서 유의한 차이를 보였다. 최대입경의 변화에 대해서는 상온에서 8mm보다 13mm가 분명히 높은 강도를 보이고 저온에서는 유의한 차이를 보이지 않았다. 그리고 공극률과 온도의 변화에 대한 실험에서는 온도에 대해서는 유의한 차이를 보였지만 20%와 22% 사이의 2% 공극 차이는 내구성에 유의한 차이를 보이지 못했으며 서로간의 교호작용도 없는 것으로 나타났다. 앞으로 다공성 아스팔트 혼합물의 내구성에 미치는 요소들의 정량적인 평가를 통해 보다 내구성 있는 다공성 아스팔트포장을 개발해 나갈 필요가 있다.