• Nuclear Engineering and Technology
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• 제55권6호
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• pp.1988-1993
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• 2023

This experimental study investigated the effect of silica fume mixed in concrete blocks on laser-induced explosion behavior. We used a 5.3 kW fiber laser as a thermal source to induce explosive spalling on a concrete surface blended with and without silica fume. An analytical approach based on the difference in the removal rate and thermal behavior was used to determine the effect of silica fume on laser-induced explosive spalling. A scanner was employed to calculate the laser-scabbled volume of the concrete surface to derive the removal rate. The removal rate of the concrete mixed with silica fume was higher than that of without silica fume. Thermal images acquired during scabbling were used to qualitatively analyze the thermal response of laser-induced explosive spalling on the concrete surface. At the early stage of laser heating, an uneven spatial distribution of surface temperature appeared on the concrete blended with silica fume because of frequent explosive spalling within a small area. By contrast, the spalling frequency was relatively lower in laser-heated concrete without silica fume. Furthermore, we observed that a larger area was removed via a single explosive spalling event owing to its high porosity.

• Corrosion Science and Technology
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• 제2권5호
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• pp.225-232
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• 2003

High temperature oxidation of SUS430 and SUS304 stainless steels in 16.7 kPa $O_2$ - 20.3 kPa $H_2O$ - balanced N2 atmosphere at 1273 K was studied focused on the scale spalling during cooling after an isothermal oxidation. Spalling of the oxide scale during cooling occurred only for SUS304 stainless steel. The oxide scale was composed of two layers and they detached at the interface between them. The reason for the spalling could not be explained only by thermal stresses applied to the specimen during heating and cooling. A new mechanism for scale spalling was proposed based on combination of thermal stresses and thermal shock caused by a fast Martensite transformation of substrate metal.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2021년도 봄 학술논문 발표대회
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• pp.237-238
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• 2021

This study evaluated the vapor pressure and thermal stress of high-strength concrete according to spalling type. As a result, it was confirmed that the internal temperature gradient of the concrete varies depending on the heating rate, and the vapor pressure and thermal stress of the concrete are the main factors of spalling. In addition, it was confirmed that spalling type varies depending on the vapor pressure and thermal stress of the concrete.

• Advances in concrete construction
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• 제4권1호
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• pp.1-14
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• 2016

In this study, high performance concrete beams and prisms with high content of PFA were heated to various temperatures up to $450^{\circ}C$ at heating rates of $1^{\circ}C/min$, $3^{\circ}C/min$ and $10^{\circ}C/min$. The thermal gradient was found to increase first with the heating time until a peak value was reached and then decrease until the thermal equilibrium was reached, measured as $115^{\circ}C$, $240^{\circ}C$ and $268^{\circ}C$ for the three heating rates. Spalling occurred on some specimens when the heating temperature was over $400^{\circ}C$ for heating rates of $3^{\circ}C/min$ and $10^{\circ}C/min$. The hygric gradient was found to reach its maximum when the thermal gradient reached its peak. This study indicates that spalling of HPC could happen when the heating temperature was high enough, and both thermal and hygric gradients reached their maxima.

• 한국전산구조공학회논문집
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• 제20권4호
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• pp.485-492
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• 2007

본 논문에서는 1편에서 얻어진 온도분포와 박리시간이력을 이용하여 지하박스구조물의 열응력을 산정하고 이에 기반한 열모멘트를 산청하였다. 또한 이때의 온도분포를 바탕으로 구조물의 열적비선형성을 고려한 극한모멘트를 산정하여 구조물의 내하력을 산정하였다. 그 결과 상부슬래브의 부모멘트 구간은 단면의 온도경사에 의해서 발생하는 열모멘트에 의해 지배받는 것으로 나타났다. 반면 정모멘트 구간은 박리에 의해 화염에 노출된 철근의 항복응력에 의해 지배받는 것으로 나타났다.

• 한국세라믹학회지
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• 제30권9호
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• pp.747-753
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• 1993

The investigation was carried out to study the behaviors of the pore size and porosity, the mechanical strength, the resistance to thermal spallings and slag attacks according to particle sizes of starting raw materials in porous high Alumina ceramics. This porous ceramics have been used in processing of the clean steel by the blowing of the inert gas. The required properties in the practice are the suitable pores size, the sharp pores distribution for a uniform blowing of the gas, the strong corrosion resistance to slags and molten metals and the resistance to thermal spalling. The optimized properties in porous high alumina ceramics of the specimen No. 3 was found to be the very low slag intrusion and the superior resistance to thermal spalling because of the suitable pore size of 2.5${\mu}{\textrm}{m}$, the porosity of 30% and the high sinterability.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(II)
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• pp.37-40
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• 2005

Recently, in order to reduce the spalling of high strength concrete under fire, the addition of organic fibres to high strength concrete has been investigated. In this study, the effect of thermal characteristic of organic fibres on the spalling of high strength concrete was experimantally investigated. Two types of fibre, polypropylene(PP) and polyvinyl alcohol(PVA) fibres, were selected, and the strength level of concrete was correnponding to the design strength of 80MPa. As a result, it appears that when the remaining ratios(by weight) of fibre at 300$^{circ}C$ and 350$^{circ}C$ are less than 80$\%$ and 50$\%$, respectively, the spalling of high strength concrete is prevented.

• 콘크리트학회논문집
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• 제24권5호
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• pp.605-612
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• 2012

콘크리트의 폭렬 발생 메커니즘에 대해서는 수증기압력에 의한 파괴, 내 외부의 온도 차이에 의해 발생하는 표면 압축력에 의한 파괴, 앞선 두 가지 요인의 복합작용에 의한 파괴가 있다. 이러한 폭렬에 영향을 주는 요인은 콘크리트 자체의 재료적 특성과 관계된 내부 요인과 환경에 의한 외부 요인으로 나눌 수 있으며 폭렬 현상을 이해하기 위해서는 두 가지 요인에 대한 충분한 고려가 필요하다. 외부 환경의 요소로써 가열 속도가 다른 경우 콘크리트 내부의 수분응집 및 수증기압력의 거동이 달라질 것으로 판단된다. 따라서 이 연구에서는 30, 50, 70, 90, 110 MPa의 다양한 강도 영역의 콘크리트를 대상으로 ISO-834 표준가열곡선과 $1^{\circ}C/min$의 가열 속도를 적용하여 가열 속도에 따른 콘크리트의 폭렬 성상 및 수증기압력, 열팽창 변형을 평가하였다. 실험 결과 콘크리트의 폭렬은 급속 가열조건에서 발생하며, 콘크리트가 고강도화될수록 폭렬에 의한 단면손실량이 증가하였다. 또한, 가열 초기에 콘크리트 표면부의 수증기압력 상승 속도 및 가열 속도에 따른 열팽창에 의한 초기압력 상쇄효과가 콘크리트의 폭렬 발생에 중요한 영향을 미치는 것으로 나타났다.

• Computers and Concrete
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• 제5권4호
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• pp.279-293
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• 2008

In the present paper a 3D thermo-hygro-mechanical model for concrete is used to study explosive spalling of concrete cover at high temperature. For a given boundary conditions the distribution of moisture, pore pressure, temperature, stresses and strains are calculated by employing a three-dimensional transient finite element analysis. The used thermo-hygro-mechanical model accounts for the interaction between hygral and thermal properties of concrete. Moreover, these properties are coupled with the mechanical properties of concrete, i.e., it is assumed that the mechanical properties (damage) have an effect on distribution of moisture (pore pressure) and temperature. Stresses in concrete are calculated by employing temperature dependent microplane model. To study explosive spalling of concrete cover, a 3D finite element analysis of a concrete slab, which was locally exposed to high temperature, is performed. It is shown that relatively high pore pressure in concrete can cause explosive spalling. The numerical results indicate that the governing parameter that controls spalling is permeability of concrete. It is also shown that possible buckling of a concrete layer in the spalling zone increases the risk for explosive spalling.

• 한국구조물진단유지관리공학회 논문집
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• 제11권6호
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• pp.193-200
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• 2007

고온을 받는 고강도 콘크리트의 폭렬현상을 해석하기 위하여 온도해석, 열응력해석 및 수분이동 해석과 더불어 콘크리트 피복의 박리여부까지 고려하여야 하는 매우 복잡하고 어려운 해석과정이 요구되나 아직 이에 대한 연구가 거의 없는 실정이다. 본 연구에서는 수증기 압력을 온도와 피복두께의 함수로서 정의하고 또한 적합조건을 이용함으로써 피복콘크리트의 박리여부를 예측할 수 있는 실용적인 폭렬해석 알고리즘을 개발하였다. 폭렬해석결과 콘크리트 강도가 증가 할수록 PP섬유량이 적을수록 폭렬현상이 심하게 발생하였으며, 이는 기존의 실험결과와 유사한 경향을 나타내어 향후 고강도 콘크리트 내화설계를 위한 폭렬해석 시 유용하게 활용될 수 있을 것으로 기대된다.