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소형석,Stephen Geoffrey Millard 한국콘크리트학회 2007 International Journal of Concrete Structures and M Vol.1 No.1
This paper discusses a method of measuring transient potential response of a corrosion interface to a small galvanostatic pulse perturbation for a rapid assessment of the corrosion rate of reinforcing steel in concrete structures. Measurements were taken on 100mm sections of steel bars which were subjected to a wide range of corrosion conditions, from passive steel to actively corroding steel. The duration of the applied galvanostatic pulse was varied between 5s and 180s, and the lateral distance of the point of measurement on the steel bar varied from zero to 400mm. The result of the electrochemical transient response was investigated using a typical sampling rate of 1 kHz. Analysis of the transient potential response to the applied galvanostatic pulse has enabled the separation of equivalent electronic components so that the components of a series of capacitances and resistances, whose values are dependent on the corrosion condition of the reinforcing steel, could be isolated. The corrosion rate was calculated from a summation of the separate resistive components, which were associated with the corrosion interface, and was compared with the corrosion rate obtained from linear polarization resistance (LPR) method. The results show that the galvanostatic pulse transient technique enables the components of the polarization resistance to be evaluated separately so as to give more reliable corrosion rate values than those obtained from the LPR method. Additionally, this paper shows how the galvanostatic pulse transient response technique can be implemented. An appropriate measurement time for passive and actively corroding reinforcing steel is suggested for the galvanostatic pulse transient response measurements in the field site.
소형석 대한건축학회지회연합회 2010 대한건축학회연합논문집 Vol.12 No.4
본 연구에서는 외부 유해물질의 침투에 대한 콘크리트 자체의 저항성, 즉 콘크리트의 물질 이동특성을 투기성에 의해 평가하고 그 결과를 콘크리트의 세공구조 특성과 함께 분석하였으며, 각 투기계수와 6개월 침지실험(10% NaCl 용액)에 의한 염소이온 침투 깊이 및 염소이온 침투로 인해 야기된 철근의 부식율의 관계를 직접 비교?분석함으로써 염해로 인한 철근의 부식에 미치는 콘크리트 투기성의 영향을 종합적으로 평가하고자 하였다.
Strength and Microstructure of Reactive Powder Concrete Using Ternary Pozzolanic Materials
소형석,KHULGADAIJANCHIVDORJ,이제방,장홍석,소승영 한국건축시공학회 2013 한국건축시공학회지 Vol.13 No.1
To consider the practicality and economic feasibility of developing reactive powder concrete (RPC), the strength and microstructure properties of RPC using ternary pozzolanic materials (silica fume, blast furnace slag, fly ash) were investigated in this study. Through the investigation, it was found that the compressive strength of RPC using ternary pozzolanic materials was increased significantly compared to that of the original RPC containing silica fume only. A considerable improvement in the flexural strength of RPC using ternary pozzolanic materials was found, and then the utilization of a structural member subjected to bending was expected. The X-ray diffractometer (XRD) analysis and Scanning Electronic Microscope (SEM) revealed that the microstructure of RPC was denser using the ternary pozzolanic materials than the original RPC.
고온에 노출된 콘크리트의 잔존강도에 미치는 냉각방법의 영향
소형석,박창선,강재홍,소승영 대한건축학회지회연합회 2016 대한건축학회연합논문집 Vol.18 No.2
본 연구는 고온에 노출된 콘크리트의 잔존강도에 미치는 냉각방법의 영향을 실험적으로 평가한 것으로 화재로 인해 손상 받은 콘크리트구조물의 피해정도 파악과 이에 따른 보수 및 보강대책 수립을 위한 기초자료를 제공하고자 수행되었다. 시험결과, 수냉(water quenching)으로 냉각된 콘크리트의 압축강도 잔존률은 300℃에서 0.77, 500℃에서 0.57, 800℃에서 0(붕괴)으로 Eurocode에서 제시하고 있는 0.85, 0.60, 0.15 보다 낮았다. 가열온도 및 냉각방법에 따른 각 콘크리트의 잔존 쪼갬 인장강도는 압축강도 보다 큰 폭으로, 거의 일직선으로 감소하고 있어 그 손상정도가 심함을 알 수 있었고, 특히 물-시멘트비가 높을수록, 수냉으로 냉각될 경우 붕괴에 이르는 가열온도가 낮아져 콘크리트구조물의 내화설계시 이에 대한 주의가 요망된다. 서냉(furnace cooling)으로 냉각된 콘크리트의 전공극률은 가열 전 콘크리트에 비해 약 1.19배 증가되었지만, 수냉의 경우는 서냉 뿐 아니라 가열 전 콘크리트 보다 낮게 나타났으며, 이는 고온하에서 분해된 시멘트 수화물의 일부가 수분의 공급으로 재수화(re-hydration)됨에 기인된 결과로서 보다 치밀한 미세구조를 갖는 것으로 판단된다. This paper was to investigate the effect of cooling methods on residual compressive and tensile strengths of normal strength concrete (NSC) after they were exposed to various high temperature grades (300, 500, 800, 1000℃). Test results showed that cooling method has a significant effect on the residual compressive and tensile strength. Water cooling, which resulted in a significant thermal shock, caused a bit more severe deterioration in strength compared to furnace cooling. The thermal shock might lead to spalling in NSC. The residual compressive strength was decreased in the range of 0-57% of the original strength for water cooling and 27-76% for furnace cooling at 500℃. Mercury intrusion porosimetry tests were carried out to measure variation in the pore structure of concrete. Significant changes in the cumulative pore volume curves before and after high temperatures were observed. However, the porosity of concrete with cooling methods was not significant. Water cooling caused a denser microstructure than furnace cooling due in part to the re-hydration of the components, which resulted from the decomposition of hardened cement mortar in concrete at high temperature.
소형석,최승훈,서기석,서정석,소승영 대한토목학회 2014 KSCE JOURNAL OF CIVIL ENGINEERING Vol.18 No.7
This paper discusses the properties of chloride ion diffusion of saturated concrete subjected to salt attack under high temperature conditions. Immersion tests were conducted for various concrete specimens of plain and fly-ash concrete with three values of water- binder ratio (W/B=40, 50, 60%) in 3.5% NaCl solution, which were controlled at four levels of temperature, i.e. 20, 40, 65, and 90℃. The depth of chloride ion penetration and the chloride profiles of concrete were investigated by using the potentiometric titration method (AgNO 3 ), and the apparent diffusion coefficient was predicted from the measured chloride profiles. The influence of temperature on the diffusion coefficient of chloride ion was discussed, by using the Arrhenius equation. Test results indicated that the apparent diffusion coefficient of chloride ion of concrete increases remarkably along with temperature rise, and there was a linear relation between the natural logarithm values of the diffusion coefficients and the reciprocal of the temperature from the Arrhenius plots. Concrete with lower water-binder ratio has a tendency towards having higher temperature dependency, and the activation energy of fly-ash concrete was higher than that of plain concrete under a temperature of up to 90℃.