• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
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• pp.643-648
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• 2002

A research for recycling the demolished-concrete as concrete aggregate has been concerned in all over the world. There, however, are some problems that qualities of recycled aggregates are not only largely different, but also mechanical properties of recycled aggregate concrete decrease a little in comparison with that of natural aggregate concrete. In this study, the resistance of freezing and thawing of concrete using source-concrete recycled aggregate(SRN) and demolished-concrete recycled aggregate(DRA) was investigated. Futhermore a research for improvement of freeze and thaw durability of recycled aggregate concrete was performed. Relative dynamic modulus of elasticity of SRN and DRA recycled aggregate concrete was dropped 60% before 150 of freezing and thawing cycle, and was much lower than that of control concrete. Relative dynamic modulus of elasticity of recycled aggregate concrete was increased to decrease water-cement ratio, but the freeze and thaw durability of recycled aggregate concrete was not enough improved. Futhermore, when metakaolin and silica fume were repalced, the freeze and thaw durability of recycled aggregate concrete containg metakaolin was more improved than that of silica fume.

• Journal of the Korean Wood Science and Technology
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• 제23권4호
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• pp.67-73
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• 1995

This study was undertaken to investigate the effect of heat treatment on the dynamic viscoelasticity of three species of Phyllostachys bambusoides, Phyllostachys nigra var. henonis and Phyllostachys pubescens, grown in southern Korea. The bamboo was treated for 3~24 hours at $60{\sim}180^{\circ}C$, and then was treated in a climatic chamber for 3~48 hours at $40^{\circ}C$ and 95% relative humidity. The results obtained are summarized as follows : 1. Dynamic Young's modulus decreased with increasing temperature and duration of the heat treatment. 2. Internal friction decreased with increasing treatment duration. 3. Moisture absorption decreased with increasing temperature and duration of the heat treatment. 4. Dynamic viscoelasticity decreased, whereas internal friction slowly increased, with increasing moisture content.

• 콘크리트학회논문집
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• 제23권1호
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• pp.23-30
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• 2011

이 연구는 콘크리트의 내구성 저하요인인 해수침식 및 동결융해 반복작용을 받은 콘크리트의 성능저하 정도를 실험적으로 고찰하기 위하여 포틀랜드 및 혼합시멘트를 사용하여 콘크리트 공시체를 제조한 후 상대동탄성계수, 압축강도 변화 및 기기분석을 통하여 성능저하 원인을 구명하였다. 동결융해 520싸이클까지의 결과 보통포틀랜드 및 저열포틀랜드시멘트는 75% 이상의 상대동탄성계수와 압축강도가 내황산염포틀랜드시멘트 약 44%의 값을 나타내어 상대적으로 낮은 저항성을 나타내었으며, 고로슬래그미분말을 50% 대체하여 사용한 콘크리트가 혼합시멘트계 콘크리트 중 가장 우수한 동결융해 저항성을 나타내었다. 혼합시멘트계 콘크리트의 해수침식 유 무에 따라 비교한 결과, 고로슬래그미분말 콘크리트의 잠재수경성 촉진으로 동결융해 저항성이 우수하였으나, 실리카퓸을 혼합한 콘크리트는 해수침식에 의한 성능저하가 발생하여 동결융해 저항성이 낮아지는 경향을 나타내었고, 해수침식 및 동결융해 작용을 받은 보통포틀랜드 콘크리트는 동결융해 작용에 의한 쏘마싸이트 피크와 해수침식에 의한 석고 및 프리델 염분 피크가 주로 검출되고, 고로슬래그미분말을 혼합한 콘크리트는 해수침식의 유 무에 상관없이 좋은 결과를 나타내었다.

• 한국건설순환자원학회논문집
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• 제9권4호
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• pp.419-424
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• 2021

콘크리트의 압축강도 추정에 널리 사용하는 반발경도법을 이용하여 콘크리트 표면의 동해손상을 초기에 판정할 수 있는 가능성을 검토하고자 하였다. 이를 위하여 동결융해 열화조건에 다면으로 노출된 콘크리트와 단면으로 노출된 콘크리트에 대하여 반발경도와 상대동탄성계수를 측정하여 콘크리트 표면 손상도를 비교하였다. 반발경도에 의한 동해손상이 단면 노출 콘크리트 시험체에 대해서는 150싸이클 빠르게 계측되었으며, 다면 노출 시험체에 대해서는 50싸이클 빠르게 계측되었다. 따라서 반발경도법이 공명진동법보다 콘크리트 표면 손상을 신속하게 판정할 수 있는 것으로 사료된다

• 한국구조물진단유지관리공학회 논문집
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• 제27권6호
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• pp.144-151
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• 2023

이 연구에서는 동결융해 작용을 받는 다양한 콘크리트 배합에 대한 실험결과를 수집하여 데이터베이스를 구축하였다. 이를 바탕으로 동결융해 작용을 받는 콘크리트의 인공지능 기반 내구성능 평가모델을 개발하였으며, 회귀분석을 통해 상대동탄성계수 추정식을 도출하였다. 제안된 인공신경망 모델의 오류율과 결정계수는 각각 약 10.4%와 0.7이었으며, 회귀분석 추정식도 유사한 결과를 나타내었다. 따라서, 제안된 인공신경망 모델 및 회귀분석 추정식은 다양한 배합의 동결융해 작용을 받는 콘크리트에 대한 상대동탄성계수를 추정하는 데에 활용될 수 있을 것으로 판단된다.

• Geomechanics and Engineering
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• 제36권4호
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• pp.317-328
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• 2024

Adopting a rational engineering methodology for building structures on sandy-clay soil layers has become increasingly important since it is crucial when structures erected on them often face seismic and cyclic wave loads. Such loads can cause a reduction in the stiffness, strength, and stability of the structure, particularly under un-drained conditions. Hence, this study aims to investigate how the dynamic properties of sand-clay mixtures are affected by loading frequency and clay content. Cyclic triaxial tests were performed on a total of 36 samples, comprising pure sand with a relative density of 60% and sand with varying percentages of clay. The tests were conducted under confining pressures of 50 and 100 kPa, and the samples' dynamic behavior was analyzed at loading frequencies of 0.1, 1, and 4 Hz. The findings indicate that an increase in confining pressure leads to greater inter-particle interaction and a reduced void ratio, which results in an increase in the soil's shear modulus. An increase in the shear strength and confinement of the samples led to a decrease in energy dissipation and damping ratio. Changes in loading frequency showed that as the frequency increased, the damping ratio decreased, and the strength of the samples increased. Increasing the loading frequency not only reflects changes in frequency but also reduces the relative permeability and enhances the resistance of samples. An analysis of the dynamic properties of sand and sand-clay mixtures indicates that the introduction of clay to a sand sample reduces the shear modulus and permeability properties.

• 한국도로학회논문집
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• 제16권2호
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• pp.43-52
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• 2014

PURPOSES : To solve problems in current compaction control DCPT(Dynamic Cone Penetrometer Test), highly correlated with various testing methods, simple, and economic is being applied. However, it、s hard to utilize DCPT results due to the few numerical analyses for DCPT have been performed and the lack of data accumulation. Therefore, this study tried to verify the validation of numerical modeling for DCPT by comparing and analyzing the results of numerical analyses with field tests. METHODS: The ground elastic modulus and PR(Penetration Rate) value were estimated by using PFC(Particle Flow Code) 3D program based on the discrete element method. Those values were compared and analyzed with the result of field tests. Also, back analysis was conducted to describe ground elastic modulus of field tests. RESULTS : Relative errors of PR value between the numerical analyses and field tests were calculated to be comparatively low. Also, the relationship between elastic modulus and PR value turned out to be similar. CONCLUSIONS : Numerical modeling of DCPT is considered to be suitable for describing field tests by carrying out numerical analysis using PFC 3D program.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2016년도 춘계 학술논문 발표대회
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• pp.181-182
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• 2016

We developed eco-friendly lightweight concrete in order to apply eco-friendly lightweight concrete into structural wall or slab of shallow depth urban railway system. However, since lightweight aggregate has different structural feature of porous and it has been overvalued at current KS standard when applied, we did compare the characteristics of freezing and thawing of normal weight aggregate concrete by comparative test method(KS, ASTM). According to test method, there was a big difference of dynamic elastic modulus in lightweight concrete rather than in normal weight aggregate concrete. The big absorption factor in lightweight aggregate is main reason for that. For more detail, in KS law in which only 14 days water curing is carried out, the big amount of moisture in lightweight aggregate is frozen and high heaving pressure occurs and finally that lead to destruction of lightweight concrete. Therefore, it is considered that in case of lightweight concrete, resistibility against freezing and thawing has been undervalued in domestic KS law compared to ASTM law, which is overseas standard. So, a variety of examination about testing criteria and rule would be necessary for exact assessment of lightweight concrete.

• 한국지반환경공학회 논문집
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• 제15권10호
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• pp.29-34
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• 2014

본 연구에서는 다공성 실리카를 사용하여 시멘트계 고화재의 유해성을 개선한 경화토의 기후변화에 대한 강도특성을 규명하기 위하여 습윤건조 반복시험을 수행하여 경화토가 기후영향을 받기 전과 후의 강도특성을 규명하고자 한다. 본 연구에 사용된 경화토는 주위에서 쉽게 구할 수 있는 화강풍화토 및 우드칩을 사용하였으며, 일축압축시험을 위한 공시체는 지름 50 mm, 높이 100 mm의 크기로 혼합토 중량대비 실리카의 혼합비율을 5 %, 10 %, 15 %로 변화시키고 각 단계별로 우드칩을 0.5 %, 1.0 %, 1.5 % 혼합하여 제작하고 7, 14, 28일 동안 상온으로 양생시킨 후 습윤건조 반복과정을 0, 3, 6, 12 cycle을 반복하여 역학적인 특성을 평가하였다. 또한 습윤건조 전후의 상대동탄성계수 변화를 평가하기 위하여 각 사이클이 종료되면 동탄성시험을 수행하였다.

• 한국환경복원기술학회지
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• 제9권3호
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• pp.17-25
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• 2006

To increase freeze-thaw resistance of porous concrete, this study examined physical properties of polymer by replacing paste used as a binding material with polymer, using unsaturated polyester and epoxy resin, and changing the mixing ratio of polymer. According to the result of this study, when the mixing ratio of resin paste to aggregates was 11 to 16%, voids volume was 33 to 37% and unit weight was about 1620 to 1720kg/$m^3$. In comparison with previous studies using cement paste, voids volume increased by about 7 to 16%, while unit weight decreased by about 100 to 300kg/$m^3$. Compressive strength was 90 to 155kg/$cm^2$ at the age of 7 days, which was 5-40kg/$cm^2$ bigger than porous concrete using cement paste. From a viewpoint of freeze-thaw resistance, it was identified that pluse velocity fell by 0.23km/sec, about 7% of the original velocity, when the cycle of freeze-thaw was repeated 300 times. In spite of 300 repetitions of the cycle, relative dynamic modulus of elasticity was more than 60%, which suggested that its freeze-thaw resistance was more excellent compared with the result that relative dynamic modulus of elasticity of porous concrete using cement paste was 60 % or less under the condition of 80 repetitions of freeze-thaw cycle.