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배합 및 양생조건이 폴리프로필렌섬유보강 초고강도 시멘트 복합체의 강도발현 특성에 미치는 영향
소형석(So Hyoung-Seok),진성훈(Jin Sung-Hoon) 대한건축학회 2010 大韓建築學會論文集 : 構造系 Vol.26 No.5
Fiber Reinforced Ultra-High Cementitious Composite (FR-UHCC) is an ultra high-strength and high ductility composite material which has shown some promises in the civil engineering community by its advanced mechanical properties. However, due to the use of very fine sand instead of ordinary aggregate, the cement factor of the FR-UHCC is as high as 900~1000 ㎏/㎥. And its density is as high as 3.0 g/㎤ by pressing fresh FR-UHCC samples in order to improve the strength. High density and high cement content may be a weakness for practicality and economic feasibility. This study is an elementary experiment to develop the FR-UHCC considered the practicality and economical efficiency, for that the various FR-UHCC was made using the constitute factors and curing conditions. And the influence of the parameters on the strength development of FR-UHCC was investigated. The result has shown that it is possible to produce ultra-high strength FR-UHCC with a density as low as 1.82 g/㎤ by the autoclave curing condition (160℃) and increasing of the silica fume/cement ratio (SF/C=80%). And an economical high strength FR-UHCC with the cement contents less than 600 ㎏/㎥ (which contains high-volume of the blast furnace slag) is produced in this study, and its compressive strength is 144 ㎫ and the density is 2.17 g/㎤.
소형석(So Hyoung-Seok) 대한건축학회 2009 大韓建築學會論文集 : 構造系 Vol.25 No.9
In the alkaline environment of concrete, the reinforcement is protected against anodic iron dissolution by a passive layer on steel surface. However, the drop in pH of the concrete pore water due to carbonation as well as chloride concentrations exceeding the threshold value will cause an extended or local breakdown of the passive layer, thus encouraging the anodic step of iron dissolution. Based on these mechanisms, the permeability of concrete such as air permeability could control a quantitative indication of potential corrosion rate. This paper reports the influence of air permeability of concrete on reinforcement corrosion due to carbonation of concrete in RC structures. The investigation has been carried out on 21 types of concrete, which are made by some parameters such as different levels of water-binder ratio, the type and replacement ratio of admixture materials, in order to measure the air permeability, depth of carbonation and corrosion rate of reinforcing steel. As a results, air permeability of concrete is related to the corrosion rate of reinforcing steel due to carbonation as well as the depth of carbonation, and the correlation coefficients are high. However, the relationship is influenced by parameters such as the water-binder ratio and the addition of admixture materials. Thus, the coefficient of air permeability may also be used in the evaluation and rehabilitation of older RC structures as well as for estimating the remaining service life in the reinforcement corrosion due to carbonation.
강섬유 보강 초고강도 시멘트 복합체의 강도발현 특성에 관한 실험적 연구
소형석(So Hyoung-Seok),소승영(So Seung-Young) 대한건축학회 2009 大韓建築學會論文集 : 構造系 Vol.25 No.7
Recently, considerable effort has been invested in research and development more highly effective construction materials due to the increasing of the multi-storied and large-sized buildings. The ultra-high strength steel fiber reinforced cementitious composites (UHS-SFRCC) are an ultra-high strength and high ductility composite material with advanced mechanical properties,and has shown some promise in the civil engineering community. In this study, as a series of the planned research to develope the practical UHS-SFRCC considered an economical efficiency. various UHS-SFRCC were made by some experimental factors such as the type and replacement ratio of admixture material, use of an alkaline stimulant, curing conditions, and the influence of experimental factors on strength development of UHS-SFRCC was discussed with the microstructure of them. As a results, the total porosity of UHS-SFRCC was significantly reduced by using appropriate silica fume and blast furnace slag combined, in consequence, the compressive and flexural strength was increased. There was no effect of NaOH as an alkaline stimulant to improve the compressive and flexural strength of UHS-SFRCC.. The total porosity of UHS-SFRCC was significantly reduced by the steam curing (90℃, but the volume of pore diameters with large size in the composites was also increased. The UHS-SFRCC with the range of compressive strength 154MPa and flexural strength 33MPa was made using silica fume, blast furnace slag, quartz sand(below 0.5mm), steel fiber in the atmosphere curing condition of 20℃.
철근콘크리트구조물에서 콘크리트의 전기저항 측정에 미치는 내부철근 및 환경변수의 영향
소형석(So Hyoung-Seok) 대한건축학회 2009 大韓建築學會論文集 : 構造系 Vol.25 No.6
The measurement of concrete resistivity, when used in conjunction with potential mapping, may be used to assess the probable location and severity of reinforcement corrosion problems in in-situ RC structures. However, the presence of the reinforcing steel may itself cause an error in the measurement of concrete resistivity by providing an electrical short circuit. In this paper, the rate of corrosion of steel embedded in concrete has been evaluated by the measurement of concrete resistivity using the Wenner technique (4-probe array system) and compared with the results measured by linear polarization resistance(LPR) method which has been developed to direct measure the corrosion rate of reinforcing steel in concrete. The influence of reinforcing steel on the measurement of concrete resistivity has been also investigated using steel reinforcement with a number of different diameters, cover depth of concrete and the presence of chloride ions in concrete, and observed the effect of environmental factors on the concrete resistivity measurements to assess externally exposed reinforced concrete. The results was shown that the measurement of concrete resistivity promises to be taken quickly, accurately and without causing damage to in-situ reinforced concrete structures, in the assessment of the presence and rate of corrosion of reinforcing steel in concrete. However, reading was influenced by the presence of reinforcing bars and its influence was increased with increasing of the diameter of steel bar and with decreasing of concrete cover depth and compressive strength of concrete. The measurement of concrete resistivity was significantly influenced by the ambient temperature and rainfall.