• Advances in concrete construction
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• 제6권2호
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• pp.159-175
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• 2018

The main aim of this study is to investigate the possible effects of metakaolin on strength and durability properties of concrete. For this purpose, concrete mixtures are produced by substituting cement with metakaolin 0, 5, 10 and 20% by weight. The amount of binder for the concrete mixtures are 300 and $400kg/m^3$ with a constant water to cement ratio of 0.6. Compressive and bending strengths, freeze-thaw and high-temperature resistances, capillary coefficients and rapid chloride permeability properties were determined and compared each other. Because of all the experiments conducted, it has been found that the use of metakaolin as a pozzolanic additive in concrete have positive effects especially on compressive and bending strengths, capillary, rapid chloride permeability, freeze-thaw resistance, and high temperatures, up to $800^{\circ}C$. The results indicated that the performance of concrete can be enhanced by metakaolin. Particularly, compressive strength and durability properties have found to be improved with increasing metakaolin content which is attributed to pozzolanic activity and filler effect. Furthermore, metakaolin has relatively positive impacts under elevated temperatures and freeze-thaw effects. However, almost all the strengths of entire concrete specimens are lost at $800^{\circ}C$. Consequently, the optimum metakaolin substitution ratio can be suggested to be 20% as per this study.

• Advances in concrete construction
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• 제6권4호
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• pp.363-373
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• 2018

Portland cement pervious concrete (PCPC) is an effective pavement material to solve or reduce the urban waterlogging problems. The Mechanical properties, the permeability, the abrasion resistance and the frost resistance of PCPC without fine aggregate were investigated. The increase of porosity was achieved by fixing the dosage of coarse aggregate and reducing the amount of cement paste. The results show that the compressive strength and the flexural strength of PCPC decrease with the increase of porosity. The permeability coefficient and the wear loss of PCPC increase with the increase of the porosity. The compressive strength and the flexural strength of PCPC subjected to 25 freeze-thaw cycles are reduced by 13.7%-17.8% and 10.6%-18.3%, respectively. For PCPC subjected to the same freeze-thaw cycles, the mass loss firstly increases and then decreases with the increase of the porosity. The relative dynamic modulus elasticity decreases with the increase of freeze-thaw cycles. And the lower the PCPC porosity is, the more obvious the dynamic modulus elasticity decreases.

• 한국임상수의학회지
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• 제17권1호
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• pp.121-128
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• 2000

The effects of cryosurgery on tear production and histological changes of the third eyelid were studied in dogs. Clinically normal 12 mixed breeds weighing 2∼6 kg were divided into three groups and treated as follows; 45 seconds double freeze-thaw treated group, 60 seconds double freeze-thaw treated group and 90 seconds double freeze-thaw treated group. The significant decrease of the tear production after cryosurgery was shown in all groups throughout the observed periods(p<0.05). However, there was no difference among groups. The main complications after cryosurgery were chemosis and conjunctival injection. Other complications such as eyelid edema, eyelid depigmentation and keratitis were more preominent in group III compared to those of groups I and II. On histopathological examination, chronic inflammatory changes and regeneration of the third eyelid glands were noted in group I and predominated loss of the third eyelid glands and necrosis of hyaline cartilage were observed in group III However, such changes were less appeared in group II. The results of this study suggested that double freeze-thaw cryosurgery for 60 seconds on the third eyelid glands would be the most effective method for treating tear staining syndrome.

• Geomechanics and Engineering
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• 제14권3호
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• pp.301-306
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• 2018

Stabilization of clayey soil has been studied from past to present by mixing different additives to the soil to increase its strength and durability. In recent years, there has been an increasing interest in stabilization of soils with natural pozzolans. Despite this, very few studies have investigated the impact of pozzolanic additives under freeze-thaw cycling. This paper presents the results of an experimental research study on the durability behavior of clayey soils treated with lime and perlite. For this purpose, soil was stabilized with 6% lime content by weight of dry soil (optimum lime ratio of the the soil), perlite was mixed with it in 0%, 5%, 10%, 20%, 25% and 30% proportions. Test specimens were compacted in the laboratory and cured for 7, 28 and 84 days, after which they were tested for unconfined compression tests. In addition to this, they were subjected to 12 closed system freeze-thaw cycles after curing for 28 days. The results show that the addition of perlite as a pozzolanic additive to lime stabilized soil improves the strength and durability. Unconfined compressive strength increases with increased perlite content. The findings indicate that using natural pozzolan which is cheaper than lime, has positive effect in strength and durability of soils and can result cost reduction of stabilization.

• 터널과지하공간
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• 제6권2호
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• pp.144-156
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• 1996

The deformation behaviors under uniaxial compressive cyclic loading were investigated for fresh rocks and freeze-thaw cycled samples. The Pocheon granite which is one of the most popular building stone in Korea was selected for tests. 0.5 Hz and 50% of dynamic strength were used as test conditions for frequency and fatigue span, respectively. For freezethaw procedure, sample were frozen for 3 hours under the temperature of -2$0^{\circ}C$ and then followed 3 hours thawing under the temperature of +2$0^{\circ}C$. Twenty seven samples were used as untreated and seventy three for freeze-thaw samples. No failure occurred up to 15000 cycles at the stress level of 60% of dynamic strength, indicating that the lowest strees level for fatigue failure may be around 60% of dynamic strength. Permanent strain and damping capacity curves show that there were three stages when rock behaves like under creep. Young's moduli were increased and Possion's ratios were decreased with the increase of the number of cycles. Possion's ratios varied more rapidly than Young's moduli did with the increase of the number of cycles. This may represent that most microcracks developed by fatigue stress are parallel to the axis of loading. The deformation behavior of freeze-thaw cycled samples were almost the same as that of untreated samples. However, the result of freeze-thaw cycled samples showed lower regression constant, indicating that the physical durability of rock is much lowered because of cyclic temperature variation.

• 한국지형학회지
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• 제19권3호
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• pp.109-121
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• 2012

한라산 정상의 백록담 서북벽 표고 1,860m 지점에서 18개월간 용암돔 암벽의 표면 온도를 향별로 관측하여 동결융해 사이클의 빈도와 출현 시기, 동결기의 암온 저하량을 밝혔다. 관측 지점에는 일주기와 연주기의 동결융해 사이클이 나타난다. 유효동결융해 사이클을 포함하여 일주기성 동결융해 사이클은 북동향 암벽보다 남서향 암벽에서 더 많이 발생한다. 일주기성 동결융해 사이클은 남서향 암벽에서는 2월과 3월에, 북동향 암벽에서는 11월과 4월에 집중적으로 출현한다. 또한 남서향 암벽에서는 11월 중순~4월 중순, 북동향 암벽에서는 11월 초순~4월 하순에 걸쳐 $0^{\circ}C$ 이하의 암온이 지속되는 계절적 동결기가 출현함으로써 연주기성 동결융해 사이클도 확인된다. 동결기의 암온 저하량은 동결지수가 더 높은 북동향 암벽에서 더 크고, 동결파쇄의 최적 온도 기준점으로 알려진 $-3^{\circ}C$ 이하의 지속시간도 북동향 암벽에서 더 길어 북동향 암벽이 남서향 암벽보다 일주기성 동결융해 사이클의 빈도는 낮아도 동결 강도는 더 큰 것으로 보인다. 따라서 암벽의 향에 따른 일사 조건의 차이가 동결융해 사이클의 빈도와 동결 지속시간을 결정함으로써 일주기성 동결융해 사이클은 남서향 암벽에서, 연주기성 동결융해 사이클은 북동향 암벽에서 현저하게 출현한다. 암석의 동결파쇄는 온도 조건으로만 결정되는 것은 아니므로 식생피복, 지형적 위치, 고도, 향을 달리하는 다양한 장소의 온도 자료 축적과 함께 암석 물성과 수분 공급에 관한 조사가 필요하다.

• 한국구조물진단유지관리공학회 논문집
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• 제26권6호
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• pp.148-156
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• 2022

대부분의 국내 콘크리트 구조물이 동결융해 및 염해 환경에 동시에 노출됨에도 불구하고 현장에서의 콘크리트 내구성능 평가는 각각의 단일 작용에 의한 손상을 평가하고 있으며 염해 손상은 현장에서 코어를 별도로 채취하여 추가적인 실내 실험분석까지 요구된다. 그러나 국내에서는 2018년부터 「시설물의 안전 및 유지관리에 관한 특별법」과 「지속가능한 기반시설 관리 기본법」 등의 시설물 유지관리를 강화하는 정책들이 수립 및 시행됨에 따라 정부 및 지자체에서 안전점검 관리 대상시설물이 증대되어 시설물이 안전 점검 및 진단에 대한 효과적인 점검 간소화 기술이 필요한 실정이다. 따라서 이 연구에서는 기존의 피복부 콘크리트 품질을 평가하는 표면반발경도를 활용하여 동해 손상이 발생한 콘크리트 부위를 대상으로 염해 손상의 가속화 정도를 판단할 수 있는 방법의 가능성을 평가하고자 하였다. 이를 위하여 동결융해 촉진 환경에 노출시켜 이미 동해 손상이 발생한 콘크리트 실험체를 염수에 침지시킨 후 콘크리트 내 침투한 염화물을 분석하여 동해 손상 정도에 따른 염화물 침투 가속화 관계를 분석하였다.

• 한국구조물진단유지관리공학회 논문집
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• 제12권5호
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• pp.161-168
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• 2008

해양콘크리트의 대표적인 내구성 열화요인이라 할 수 있는 동결융해나 염해의 경우는 콘크리트내의 공극특성에 따라 침투 및 확산특성이 크게 상이하게 되는데, 이는 동결융해저항성 확보를 목적으로 사용되고 있는 AE제의 종류나 사용량 그리고 그의 경시변화 특성 등과 매우 밀접한 관계가 있다. 따라서 본 연구에서는 굳지않은 콘크리트의 목표 공기량을 각각 4~6%와 8~10%로 계획하여 실내시험을 실시한 후, 모의부재에서는 4~6%를 대상으로 평가하였다. 실험결과, 경화콘크리트의 공기량은 재령 7일에서 각각 2.5~5.2%, 재령 28일에서는 각각 2.4~5.1%정도로서 비빔직후 목표공기량의 절반수준인 것으로 나타났고, 동결융해 반복에 따른 스케일량은 목표공기량 8~10%의 경우가 4~6%에 비해 미미한 수준에서 다소 유리한 것으로 평가되었다. 한편, 모의부재에서 채취한 코어공시체의 동결융해 및 염화물 확산특성에서는 동일배합조건의 실내시험 결과에 비해 다소 불리한 것으로 나타났는데, 실내실험 결과에 비해 동결융해는 106%, 염화물 확산계수는 160% 수준인 것으로 나타났다.

• Corrosion Science and Technology
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• 제15권1호
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• pp.18-27
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• 2016

In this study, the accelerated corrosion test by combined deteriorating action of salt damage and freeze-thaw was investigated. freeze-thaw cycle is one method for corrosion testing; corrosion initiation time was measured in four types of concrete samples, i.e., two samples mixed with fly ash (FA) and blast furnace slag (BS), and the other two samples having two water/cement ratio (W/C = 0.6, 0.35) without admixture (OPC60 and OPC35). The corrosion of rebar embedded in concrete occurred most quickly at the $30^{th}$ freeze-thaw cycle. Moreover, a corrosion monitoring method with a half-cell potential measurement and relative dynamic elastic modulus derived from resonant frequency measures was conducted simultaneously. The results indicated that the corrosion of rebar occurred when the relative dynamic elastic modulus was less than 60%. Therefore, dynamic elastic modulus can be used to detect corrosion of steel bar. The results of the accelerated corrosion test exhibited significant difference according to corrosion periods combined with each test condition. Consequently, the OPC60 showed the lowest corrosion resistance among the samples.

• 콘크리트학회지
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• 제10권4호
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• pp.163-169
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• 1998

폐콘크리트로부터 생산된 재생굵은골재를 쇄석골재 대신하여 콘크리트에 활용하기 위하여 압축강도, 휨강도의 특성 및 동결융해저항성을 측정하였다. 쇄석골재로 일정비율 대체한 재생콘크리트는 보통콘크리트에 비하여 압축 및 휨강도가 낮았으며, 플라이애쉬 혼입한 재생콘크리트는 보통콘크리트와 비슷한 강도변화를 나타냈다. 동결융해저항성은 물.시멘트비, 재생굵은골재 대체율 그리고 플라이애쉬의 첨가량에 따라 차이점을 보였으나. 물.시멘트비가 낮을수록 플라이애쉬 혼입량이 적을수록 그리고 재생굵은골재 대체율이 80%일 때 저항성이 가장 우수한 것으로 나타났다.