• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 추계 학술발표회 제16권2호
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• pp.157-160
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• 2004

If concrete structure is exposed to high temperature such as long-term fire, damages affecting partial or whole structure system may occur. Therefore accurate diagnosis of deterioration is needed based on mechanism of fire deterioration in general concrete structures. Fundamental information and data on the properties of concrete exposed to high temperature are necessary. Especially, the amount of fire damage done to concrete depends on the materials, the standard design compressive strength of concrete, and heated temperature. So, the object of this study is to present data for supposed heated Temperature of deteriorated concrete by fire.

• Advances in concrete construction
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• 제9권3호
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• pp.279-287
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• 2020

This paper focuses on the engineering properties of Bentonite-Cement-Sodium silicate (BCS) grout, which was prepared by partially replacing the ordinary Portland cement in Cement-Sodium silicate grout with lithium bentonite (Li-bent) and sodium bentonite (Na-bent), respectively. The effect of different Water-to-Solid ratio (W/S) and various replacement percentages of bentonite on the apparent viscosity, bleeding, setting time, and early compressive strength of BCS grout were investigated. The XRD method was used to detect its hydration products. The results showed that both bentonites played a positive role in the stability of BCS grout, increased its apparent viscosity. Na-bent prolonged the setting time of BCS, while 5% of Li-bent shortened the setting time of BCS. The XRD analysis indicated that the hydration products between the mixture containing Na-bent and Li-bent did not differ much. Using bentonite as supplementary cementitious material (SCM) to replace partial cement is a promising way to cut down on carbon dioxide emissions and to produce low-cost, eco-friendly, non-toxic, and water-resistant grout. In addition, Li-bent was superior to Na-bent in improving the strength and the thickening of BCS grouts.

• Geomechanics and Engineering
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• 제14권6호
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• pp.553-562
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• 2018

Road construction is becoming increasingly important in marine and desert areas due to population growth and economic development. However, the load carrying capacity of pavement is of gear concern to design and geotechnical engineers because of the poor engineering properties of the soils in these areas. Therefore, stabilization of the soils is regarded as an important issue. Besides, due to the fuels combustion and carbonate decomposition, cement industry generates around 5% of global $CO_2$ emission. Thus, using bentonite as a natural pozzolan in soil stabilization is more eco-friendly than using cement. The aim of this research is to experimentally study of the stabilized marine and desert sands using deep mixing method by ordinary Portland cement and sodium bentonite. Different partial percentages of cement along with different weight percentages of sodium bentonite were added to the sands. Unconfined compression test (UCS), Energy Dispersive X-ray (EDX), and Scanning Electron Microscope (SEM) were conducted on the specimens. Moreover, a mathematical model was developed for predicting the strength of the treated soils.

• 자원리싸이클링
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• 제19권2호
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• pp.10-18
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• 2010

본 연구는 소성공정으로 MSWI fly ash를 혼합한 일차점토와 적황토 공시체의 특성을 알아보기 위하여 진행되었다. 최대 20 wt% MSWI fly ash를 혼합한 공시체는 SEM, UTM, ICP 등의 방법으로 분석되었으며, 그 결과 $P_{10}$공시체는 휨강도가 증가하였고, $R_5$공시체는 압축강도와 휨강도가 증가하였다. 또한 중금속 용출량도 기준치를 만족하였다. 이것은 MSWI fly ash가 소성공정에 의한 벽돌제조에서 기존 재료의 부분대체에 적합하다는 것을 나타내는 것이다.

• International Journal of Concrete Structures and Materials
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• 제10권1호
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• pp.39-46
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• 2016

In this study, different proportions of glass beads used for road marking were added into the concrete samples to reduce the temperature gradient through the concrete pavement thickness. It is well known that decreasing the temperature gradient reduces the risk of thermal cracking and increases the service life of concrete pavement. The extent of alkali-silica reaction (ASR) produced with partial replacement of fine aggregate by glass bead was investigated and compressive strength of concrete samples with different proportion of glass bead in their mix designs were measured in this study. Ideal results were obtained with less than 0.850 mm diameter size glass beads were used (19 % by total weight of aggregate) for C30/37 class concrete. Top and bottom surface temperatures of two different C30/37 strength class concrete slabs with and without glass beads were measured. It was identified that, using glass bead in concrete mix design, reduces the temperature differences between top and bottom surfaces of concrete pavement. The study presented herein provides important results on the necessity of regulating concrete road mix design specifications according to regions and climates to reduce the temperature gradient values which are very important in concrete road design.

• Advances in concrete construction
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• 제12권5호
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• pp.419-427
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• 2021

The overuse level of cement for civil industry has several undesirable social and ecological consequences. Substitution of cement with industrial wastes, called by-products, such as fly ash, ground granulated blast furnace slag, silica fume, metakaoline, rice husk ash, etc. as the mineral admixtures offers various advantages such as technical, economical and environmental which are very important in the era of sustainability in construction industry. The paper presents the experimental investigations for assessing the mechanical properties of the concrete made using the Pozzolanic waste materials (supplementary cementitious materials) such as fly ash and silica fume as the cement replacing materials. These materials were used in eight trial mixes with varying amount of ordinary Portland cement. These SCMs were kept in equal proportions in all the eight trial mixes. The chemical admixture (High Range Water Reducing Admixture) was also added to improve the workability of concrete. The compressive strengths for 7, 28, 40 and 90 days curing were evaluated whereas the flexural and tensile strengths corresponding to 7, 28 and 40 days curing were evaluated. The study corroborates that the Pozzolanic materials used in the present investigation as partial replacement for cement can render the sustainable concrete which can be used in the rigid pavement construction.

• 국제초고층학회논문집
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• 제10권4호
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• pp.335-344
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• 2021

In structural engineering practice, understanding the performance of composite columns under extreme loading conditions such as high-rise bulding, long span and heavy loads is essential to accuratly predicting of material responses under severe loads such as fires or earthquakes. Hitherto, the combined effect of partial axial loads and subsequent elevated temperatures on the performance of hollow steel column filled fly ash concrete have not been widely investigated. Comprehensive test was carried out to investigate the effect of elevated temperatures on partial axially loaded square hollow steel column filled fly ash concrete as reported in this paper. Four batches of hollow steel column filled fly ash concrete ( 30 percent replacement of fly ash), (HySC) and normal concrete (CFHS) were subjected to four different load levels, n_f of 20%, 30%, 40% and 50% based on ultimate column strength. Subsequently, all batches of the partially damage composite columns were exposed to transient elevated temperature up to 250℃, 450℃ and 650℃ for one hour. The overall stress - strain relationship for both types of composited columns with different concrete fillers were presented for each different partial load levels and elevated temperature exposure. Results show that CFHS column has better performance than HySC at ambient temperature with 1.03 relative difference. However, the residual ultimate compressive strength of HySC subjected to partial axial load and elevated temperature exposure present an improvement compared to CFHS column with percentage difference in range 1.9% to 18.3%. Most of HySC and CFHS column specimens failed due to local buckling at the top and middle section of the column caused by concrete crushing. The columns failed due to global buckling after prolong compression load. After the compression load was lengthened, the columns were found to fail due to global buckling except for HySC02.

• 한국구조물진단유지관리공학회 논문집
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• 제20권5호
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• pp.116-122
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• 2016

이 연구에서는 부순골재 생산과정에서 발생하는 다량의 골재 미분말이 콘크리트의 성질에 미치는 영향을 살펴보고자 하였다. 골재 미분말을 잔골재 중량의 0~30 wt.% 범위로 치환한 콘크리트에 대해 슬럼프, 공기량, 강도 및 건조수축 변화에 대한 실험을 실시하였다. 실험 결과, 골재 미분말의 사용량이 증가함에 따라 슬럼프 및 공기량이 크게 저하되는 것으로 나타났으며, 골재 미분말을 잔골재의 10~30% 치환하여 사용하였을 때 압축강도 및 인장강도가 골재 미분말을 사용하지 않은 경우에 비해 약간 증가되는 것으로 나타났다. 건조수축 변형률은 골재 미분말 사용량이 증가할수록 더 커지는 것으로 나타났다. 동일한 물시멘트비, 단위시멘트량에 대해 골재 미분말을 사용하면서 골재 미분말을 혼합하지 않은 콘크리트와 유사한 작업성을 얻기 위해 고성능감수제를 적절량 사용한 경우, 사용량에 따라 공기량은 약간 증가하고, 강도 및 건조수축 변형률은 큰 변화가 나타나지 않았다.

• Structural Engineering and Mechanics
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• 제87권6호
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• pp.585-599
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• 2023

Geopolymer concrete (GC) can be competently utilized as a practical replacement for cement to prevent a high carbon footprint and to give a direction toward sustainable concrete construction. Moreover, previous studies mostly focused on the axial response of glass fiber reinforced polymer (glass-FRP) concrete compressive elements without determining the effectiveness of repairing them after their partial damage. The goal of this study is to assess the structural effectiveness of partially damaged GC columns that have been restored using carbon fiber reinforced polymer (carbon-FRP). Bars made of glass-FRP and helix made of glass-FRP are used to reinforce these columns. For comparative study, six of the twelve circular specimens-each measuring 300 mm×1200 mm-are reinforced with steel bars, while the other four are axially strengthened using glass-FRP bars (referred to as GSG columns). The broken columns are repaired and strengthened using carbon-FRP sheets after the specimens have been subjected to concentric and eccentric compression until a 30% loss in axial strength is attained in the post-peak phase. The study investigates the effects of various variables on important response metrics like axial strength, axial deflection, load-deflection response, stiffness index, strength index, ductility index, and damage response. These variables include concentric and eccentric compression, helix pitch, steel bars, carbon-FRP wrapping, and glass-FRP bars. Both before and after the quick repair process, these metrics are evaluated. The results of the investigation show that the axial strengths of the reconstructed SSG and GSG columns are, respectively, 15.3% and 20.9% higher than those of their original counterparts. In addition, compared to their SSG counterparts, the repaired GSG samples exhibit an improvement in average ductility indices of 2.92% and a drop in average stiffness indices of 3.2%.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.865-868
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• 2008

본 연구에서는 최근 사용이 증대되고 있는 고성능 콘크리트의 폭렬현상을 방지하기 위해 일련의 연구 중 메탈라스 횡구속을 병행한 비탈형 거푸집을 사용한 고성능 콘크리트 RC기둥부재의 내화특성을 검토하였는데, 그 결과를 요약하면 다음과 같다. 유동성 및 공기량은 모두 목표 범위를 만족하였고, 압축강도는 재령 28일에서 80 MPa이상으로 고강도범위를 나타내었다. 폭렬 특성으로는 섬유를 혼입하지 않은 플레인의 경우는 심한 폭렬이 발생하였고, 나일론(이하 NY)+폴리프로필렌(이하 PP) 섬유를 0.05%를 혼입한 경우에는 표면부에만 부분적인 박리폭렬이 발생하였다. 비탈형 거푸집 변화에 따라서는 비탈형 25-20, 비탈형 50-20의 경우에는 모두 마 감재부분에 폭렬이 발생하였는데, 비탈형 50-20의 경우가 비탈형 25-20보다 양호한 폭렬방지 성능을 나타내었다. 비탈형 50-40의 경우는 폭렬이 방지되었는데 질량감소율은 10%이하로 나타났고, 온도이력은 모재표면부 최고온도가 $376.1^{\circ}C$로 가장 우수한 내화 성능을 나타내었다.