• 한국구조물진단유지관리공학회 논문집
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• 제27권1호
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• pp.30-36
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• 2023

이 연구에서는 콘크리트 표면 이미지를 활용하여 표면공극률을 평가할 수 있는 영상 분할모델을 도출하였다. 물-시멘트비가 다른 3종류의 콘크리트 실험체 (w/c = 54, 35, 및 30%) 가 제작되었으며, 광학현미경을 활용하여 2,729장의 표면 이미지를 취득하였다. 공극이 마스킹 된 표면 이미지 를 활용하여 벤치마킹 테스트, 매개변수 최적화, 최종모델 도출이 실시되었으며, 97%의 검증정확도를 나타내는 영상 분할 모델을 도출할 수 있었다. 영상 분할모델 및 X-Ray Microscope (XRM)을 통해 얻은 공극률을 비교하여 모델을 검증하였으며, 물시멘트비가 높은 시편에 대해선 모델과 XRM이 평가한 공극률이 유사하였고, 물시멘트비가 낮은 시편에 대해서는 모델이 XRM보다 공극률을 낮게 평가하는 경향을 나타내었다.

• International Journal of Concrete Structures and Materials
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• 제11권1호
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• pp.17-28
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• 2017

Although concrete is a noncombustible material, high temperatures such as those experienced during a fire have a negative effect on the mechanical properties. This paper studies the effect of elevated temperatures on the mechanical properties of limestone, quartzite and granite concrete. Samples from three different concrete mixes with limestone, quartzite and granite coarse aggregates were prepared. The test samples were subjected to temperatures ranging from 25 to $650^{\circ}C$ for a duration of 2 h. Mechanical properties of concrete including the compressive and tensile strength, modulus of elasticity, and ultimate strain in compression were obtained. Effects of temperature on resistance to degradation, thermal expansion and phase compositions of the aggregates were investigated. The results indicated that the mechanical properties of concrete are largely affected from elevated temperatures and the type of coarse aggregate used. The compressive and split tensile strength, and modulus of elasticity decreased with increasing temperature, while the ultimate strain in compression increased. Concrete made of granite coarse aggregate showed higher mechanical properties at all temperatures, followed by quartzite and limestone concretes. In addition to decomposition of cement paste, the imparity in thermal expansion behavior between cement paste and aggregates, and degradation and phase decomposition (and/or transition) of aggregates under high temperature were considered as main factors impacting the mechanical properties of concrete. The novelty of this research stems from the fact that three different aggregate types are comparatively evaluated, mechanisms are systemically analyzed, and empirical relationships are established to predict the residual compressive and tensile strength, elastic modulus, and ultimate compressive strain for concretes subjected to high temperatures.

• Advances in concrete construction
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• 제13권1호
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• pp.71-81
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• 2022

Aluminosilicate materials as precursors are heterogenous in nature, consisting of inert and partially reactive portion, and have varying proportions depending upon source materials. It is essential to assess the reactivity of precursor prior to synthesize geopolymers. Moreover, reactivity may act as decisive factor for setting molar concentration of NaOH, curing temperature and setting proportion of different precursors. In this experimental work, the reactivities of two precursors, low calcium (fly ash (FA)) and high calcium (ground granulated blast furnace slag (GGBS)), were assessed through the dissolution of aluminosilicate at (i) three molar concentrations (8, 12, and 16 M) of NaOH solution, (ii) 6 to 24 h dissolution time, and (iii) 20-100℃. Based on paratermeters influencing the reactivity, different proportions of ternary binders (two precursors and ordinary cement) were activated by the combined NaOH and Na2SiO3 solutions with two alkaline activators to precursor ratios, to synthesize the geopolymer. Reactivity results revealed that GGBS was 20-30% more reactive than FA at 20℃, at all three molar concentrations, but its reactivity decreased by 32-46% with increasing temperature due to the high calcium content. Setting time of geopolymer paste was reduced by adding GGBS due to its fast reactivity. Both GGBS and cement promoted the formation of all types of gels (i.e., C-S-H, C-A-S-H, and N-A-S-H). As a result, it was found that a specified mixing proportion could be used to improve the compressive strength over 30 MPa at both the ambient and hot curing conditions.

• 대한치과보철학회지
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• 제34권2호
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• pp.335-348
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• 1996

Retention is one of the major factors deciding the success and longevity of resin bonded restorations. The purpose of this study was to find a better resin cement and metal surface treatment method that would enhance the bonding strength. The bonding surfaces of Verabond, one of Ni-Cr-Be alloys, were treated with sandblasting(Group 1), sandblasting and EZ-Oxisor(Group 2), sandblasting and silicoating(Group 3), and than thay were bonded with All-Bond C & B, Panavia 21, Superbond C & B. The specimens were thermocycled, and the tensile bond strength was measured using the unive-rsal testing machine. Also the mode of bond failure was observed. The results were as folows. 1. The Superbond C & B showed the highest bond strength among the three resin cements and decreased in the order of Panavia 21, All-Bond C & B. There was significant differe-nce among them(p<0.05). 2. Group 3 showed the highest bond strength among the three metal surface treatment methods, and there was significant difference compared with Group 1 and Group 2(p<0.05). But there was no significant difference between Group 1 and Group 2. 3. Observing the mode of bond failure, Superbond C & B and Panavia 21 showed mostly cohesive failure in all groups. All-Bond C & B showed all types of bond failure in Group 3, but Group 1 and Group 2 showed only adhesive failure. 4. According to the results of this study, the silicoating method and 4-META containing resin cement were considered to be more acceptable for resin bonded restoration.

• Geomechanics and Engineering
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• 제15권2호
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• pp.729-738
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• 2018

Soft clay soils due to their various geotechnical problems, stabilized with different additives. Traditional additives such as cement and lime will not able to increase the soil strength properties significantly. So, it seems necessary to use new additives for increasing strength parameters of soft clay soils significantly. Among the new additives, epoxy resins have excellent physical and mechanical properties, low shrinkage, excellent resistance to chemicals and corrosive materials, etc. So, in this research, epoxy resin used for stabilization of soft clay soils. For comprehensive study, three clay soil samples with different PI and various clay mineral types were studied. A series of uniaxial tests, SEM and XRD analysis conducted on the samples. The results show that using epoxy resin increases the strength parameters such as UCS, elastic modulus and material toughness about 100 to 500 times which the increase was dependent on the type of clay minerals type in the soil. Also, In addition to water conservation, the best efficiency in the weakest and most sensitive soils is the prominent results of stabilization by epoxy resin which can be used in different climatic zones, especially in hot and dry and equatorial climate which will be faced with water scarcity.

• 한국농공학회논문집
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• 제64권1호
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• pp.91-98
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• 2022

Multi-layered geotextile tubes may have problems on its stability when used as cofferdam. This study presents the shear strength characteristics at the interface between geotextiles and a cementitious binder material to improve the stability of the multi-layered geotextile tubes. In this study, two different types of geotextiles are used. After mixing with a rapid setting cement, fly ash, sand, accelerator, and water, the cementitious binder material is prepared at the interface between two geotextile samples and cured under water for a desired period. The specimen is placed on upper and lower direct shear boxes by using clamping systems. A series of direct shear tests for two different geotextiles are performed along the curing time under three vertical stresses. Experimental results show that the shear strength at the interface between the cementitious binder material and geotextiles is greater than that at the interface between two geotextiles. For two types of geotextiles, apparent cohesion occurs at the interface between the cementitious binder material and geotextiles. In addition, the friction angles for any curing time are improved, compared to the interface between two geotextiles. The cementitious binder material suggested for the interface between two geotextiles may be useful for the reinforcement of multi-layered geotextile tubes.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1996년도 가을 학술발표회 논문집
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• pp.380-386
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• 1996

This paper presents the history of heat hydration and the core strength of underwater non-segregation concrete. Three types of cements including Type I, Type V and low-heat cement have been used to make the mass specimens for measurement of heat of hydration and also for coring. Two environments of ambient and underwater conditions have been accounted for the comparison of producing the heat of hydration and for the assessment of core strength in respect to the test specimens made under normal practice.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1995년도 봄 학술발표회 논문집
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• pp.111-117
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• 1995

The alkali-aggregate reaction is a reaction between the alkali metals in the pore water of a concrete and an unstable mineral of the aggregate. There are three types of alkali-aggregate reation which causes deterioration of concrete, such as alkali-silicate reation, alkali-carbonate reaction and alkali-silica reation. Deterioration due to alkali-silica reation is more comon than that due to either the alkali-silicate or alkali-carbonate reaction. The alkali-silica reation is a reaction between the hydroxyl ions in the pore water of a concrete and silica which exists in signigicant quantities in the aggregate. In this PAPER, Alkali-aggregate reactions of mortar made with various abroad aggregate were investigated using XRD, microscope, chemical and physical tests. In additions, the effects of the texture of aggregate, Na, K, CI ion concentrations added to the mortar, on these reactions were studied.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2023년도 가을학술발표대회논문집
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• pp.77-78
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• 2023

This paper experimentally examined the recycling of combustion by-products emitted from a combined heat and power plant using lignocellulosic biomass fuel. Physical and chemical analyzes were performed on Bio-SRF and three types of wood pellet combustion by-product samples (fly-ash, FA). As a result of the experiment, the compressive strength of mortar substituted with 5, 10, and 20% of FA compared to the cement weight was found to be excellent, and its recyclability was confirmed as a substitute for existing admixtures.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(II)
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• pp.65-68
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• 2005

Social requirements to the civil and building structures have been changed in accordance with the social and economic progress. It is very important to develop the innovative structural materials and tecnology that the social requirements appropriately. Ductility of High Performance Fiber Reinforced cementitious Composites (HPFRCC), which exhibit strain hardening and multiple crackling characteristics under the uniaxial tensile stress are drastically improved. Because ductility in tensile test are very different according to specimen shapes, three types of the direct tensile test are performed. The tensile test are performed using the tensile test specimen, dummbell-shaped specimen, and cylinder specimen. As a result, tensile performance in HPFRCC is very good comparing to cylinder specimen because of direction characteristics of fibers. It is necessary to clarify the examination method of suiting to the usage.