아치형 강섬유 혼입량에 따른 강섬유보강콘크리트의 건조수축 특성

박인호 ( Park In-ho ),김종선 ( Kim Jong-sun ),김선희 ( Kim Sun-hee ),최원창 ( Choi Wonchang ) 한국복합신소재구조학회 2024 복합신소재구조학회논문집 Vol.15 No.2

콘크리트는 수화반응에 필요한 물 이외의 자유수가 증발하게 되면 건조수축이 발생하며 이로 인해 발생한 균열은 구조물의 강도 및 내구성 저하에 영향을 미친다. 이에 건조수축에 의한 균열을 억제하기 위한 대처 방안으로 강섬유를 혼입한 강섬유보강콘크리트에 관한 연구가 진행되고 있다. 본 연구에서는 아치형 강섬유 혼입량에 따른 건조수축 특성을 파악하고 구속건조수축 변형률을 콘크리트에 발생하는 잔류 인장응력으로 치환하여 기존 연구 결과와 비교하였다. 자유건조수축 실험을 통해 아치형 강섬유 혼입량에 따른 건조수축 변형률의 저감효과는 미미한 수준임을 확인하였다. 구속건조수축 실험 결과, 아치형 강섬유 혼입량 증가에 따라 균열의 발생지연 및 균열 폭 저감에 효과적인 것으로 나타났다. 또한 아치형 강섬유를 60kg/m³ 혼입하였을 때 무보강 콘크리트에 발생하는 잔류인장응력에 비해 52.4% 높은 인장강도를 가지며 구속건조수축에 대한 저항성능이 향상될 수 있음을 확인하였다. Evaporation of water apart from that used in the concrete hydration reaction causes drying shrinkage, which affects structural strength and durability. Therefore, research is being conducted on steel-fiber-reinforced concrete to control the occurrence of cracks resulting from drying shrinkage. In this study, arched steel fibers by volume fraction are used to investigate drying shrinkage properties. For the experiments, strain resulting from restrained drying shrinkage was substituted by concrete residual tensile stress and the results were compared with those of previous experiments. It was found that arched steel fibers have minimal influence on free drying shrinkage. Meanwhile, in the restrained drying shrinkage test, increasing the volume fraction of the arched steel fibers was found to be effective in delaying crack initiation and reducing crack width. Further, at 60 kg/m³, it had a tensile strength of 52.4%, which was higher than the residual tensile stress generated in plain concrete, and improved resistance to restrained drying shrinkage.

콘크리트 배합조건에 따른 수축저감제의 건조수축 특성

김영선 ( Kim Young-sun ),김광기 ( Kim Kwang-ki ),박순전 ( Park Soon-jeon ),김정선 ( Kim Jung-sun ) 한국건축시공학회 2017 한국건축시공학회지 Vol.17 No.3

최근 소비패턴의 변화에 따라 대형마트, 아울렛 및 물류창고 등과 같은 구조물들이 증가하고 있다. 이와 같은 구조물들은 초평탄 바닥부재를 포함하고 있기 때문에 소성 및 건조수축에 의한 슬래브 부재의 균열 억제 관리를 철저하게 실시한다. 슬래브 부재의 균열을 억제하기 위한 방안으로 화학적 균열저감 방법을 사용하고 있으며, 특히 수축저감제에 대한 사용검토가 증가하고 있다. 그러나 이에 대한 국내 연구결과는 부족한 상황이다. 본 연구에서는 수축저감제를 사용한 콘크리트의 수축특성과 배합요인 변동에 따른 건조수축 특성을 검토하였다. 국내 수축저감제는 해외 고급형 수축저감제와 성능이 유사한 것으로 나타났으며, 수축저감제 사용량이 증가할수록 건조수축 억제 효과는 높아지는 것으로 나타났다. 수축저감제 1.5%를 사용한 시험체는 재령 100일에서 수축저감제를 사용하지 않은 시험체에 비해 건조수축량이 약 절반으로 나타났다. 또한, 혼화재료 사용에 대해 특별한 성능변화는 없는 것으로 확인되었다. Recently, structures such as large retailers, outlets and warehouses have been increasing in accordance with changes in consumption patterns. Since these structures include ultra-flat slab members, they are thoroughly managed to control slab cracking by the plastic and drying shrinkage. In order to control the cracking of the slab member, a chemical crack reduction method is used. In particular, the use of the shrinkage reducing agent has been examined. However, domestic research results are limited. In this study, the shrinkage properties of concrete using shrinkage reducing agent and the drying shrinkage properties according to the mixing factors were investigated. The performance of domestic shrinkage reducing agent was appeared similar to that of overseas high-grade shrinkage reducing agent. As the shrinkage reducing agent usage increased, the drying shrinkage reduction effect increased. At the age of 100 days, the dry shrinkage rate of specimen with the shrinkage reducing agent of 1.5%was shown about half that of the specimen without the shrinkage reducing agent. The shrinkage reducing agent was gound to have no specific performance change for the use of the admixture.

Internal relative humidity and drying shrinkage of hardening concrete containing lightweight and normal-weight coarse aggregates: A comparative experimental study and modeling

Elsevier 2017 Construction and Building Materials Vol.148 No.-

<P><B>Abstract</B></P> <P>The effect of lightweight and normal-weight coarse aggregates on the internal relative humidity (IRH) and drying shrinkage of hardening concrete was investigated experimentally. The compressive strength, elastic modulus, IRH, and drying shrinkage of concrete specimens were measured. Lightweight and normal-weight concretes exhibited different variations in IRH and drying shrinkage. The results suggest that drying shrinkage should be evaluated in terms of average IRH drop at equivalent age, considering the development of elastic modulus for lightweight and normal-weight hardening concretes. The model of the shrinkage coefficient can be useful for evaluating the drying shrinkage of lightweight and normal-weight hardening concretes.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The IRH and drying shrinkage of lightweight and normal-weight concrete are measured. </LI> <LI> The internal curing effect of lightweight aggregates reduces IRH drop in concrete. </LI> <LI> Drying shrinkage should be evaluated in terms of average IRH drop. </LI> <LI> A model of the shrinkage coefficient is proposed. </LI> <LI> Ultimate shrinkage is inversely proportional to the compressive strength of concrete. </LI> </UL> </P>

섬유 및 혼화제를 이용한 황토 모르타르의 수축균열 제어

문주현(Mun Ju-Hyun),양근혁(Yang Keun-Hyeok),전중규(Jeon Joong-Kyu),황혜주(Hwang Hye-Zoo) 대한건축학회 2012 大韓建築學會論文集 : 構造系 Vol.28 No.8

A total of 8 hwang-toh mortar mixes with no cement were tested to evaluate the effect of different fibers and admixtures on the control of shrinkage cracks of such mortars. The fiber types added were Lyocell, Poly-Amid and PVA, while, CSA and organic polymer were selected as the admixture. The shrinkage crack resistance of hwang-toh mortar were examined from the unrestrained drying shrinkage strain, restrained drying shrinkage and plastic shrinkage. Test results revealed that the unrestrained drying shrinkage strain of hwang-toh mortar sharply increased at an early age showing approximately 2.5 times higher values than predictions obtained from ACI 209, regardless of the addition of fibers and admixtures. In addition, cracks owing to the restrained drying shrinkage developed at the only age of 1.6 days in all test mixes; as a result, the cracking grade of hwang-toh mortar was evaluated to be high. On the other hand, the addition of fibers required a value of fiber spacing above 0.0003 in order to enhance the tensile resistance capacity of hwang-toh mortar under the restrained drying shrinkage and reduce the cracking area under the plastic shrinkage. Overall, it could be concluded that moist curing at an early age and the addition of fiber with fiber spacing above 0.0003 are practically effective in reducing shrinkage crack of hwang-toh mortar.

강섬유 인장강도에 따른 강섬유 보강 콘크리트 건조수축 특성

백대일,한성민,최기봉,윤현도,최원창 한국복합신소재구조학회 2022 복합신소재구조학회논문집 Vol.13 No.3

Much research has been conducted on steel fiber reinforced concrete (SFRC) to reduce cracks caused by drying shrinkage. Steel fiber can improve the early-age properties of concrete to increase the cracking resistance by acting as a stitch between crack faces. In this study, steel fibers with different tensile strengths were used to investigate the characteristics of drying shrinkage of SFRC. Free and restrained drying shrinkage tests were conducted, and the drying shrinkage rate was converted to the tensile strength of concrete and compared with the result of the tensile strength test. The results indicate that steel fiber has little influence on free drying shrinkage. However, for restrained drying shrinkage, as the tensile strength of steel fiber increases, it is effective in delaying the occurrence of cracks and reducing the width of cracks. In addition, steel fiber can effectively resist tensile stress caused by drying shrinkage and increases the tensile strength of SFRC, and its effectiveness increases with increasing tensile strength. 콘크리트 경화 시 발생하는 수분증발로 인한 건조수축은 콘크리트의 균열을 발생시킨다. 콘크리트에 발생하는 균열은 콘크리트의 내구성을 저하하여 안정성과 사용성에 문제를 발생시킨다. 이러한 문제점을 보안하기 위해 콘크리트에 강섬유를혼입하여 건조수축으로 인한 균열을 방지하는 강섬유 보강 콘크리트 (SFRC)에 관한 연구가 진행되고 있다. 강섬유는 콘크리트의 균열단면에서 가교역할, 부착작용을 통해 건조수축으로 인한 균열발생을 억제하고 균열 폭을 감소시키는 효과가 있다. 본 논문에서는 강섬유의 인장강도에 따른 강섬유 보강 콘크리트의 건조수축 제어성능을 평가하였다. 자유건조수축 실험과 구속건조수축 실험을 진행하였으며 실험 결과를 콘크리트의 인장응력으로 변환하여 콘크리트 직접인장실험 결과와 비교하였다. 강섬유의 자유건조수축 저감 효과는 미미하지만 강섬유의 인장강도가 증가할수록 구속건조수축으로 인한 균열제어에 효과적임을 확인하였다. 또한 강섬유의 인장강도가 증가할수록 콘크리트의 인장응력이 증가함을 확인하였다.

교량 바닥판 콘크리트의 부등건조수축 균열특성에 관한 연구

양주경(Yang Joo Kyoung),이윤(Lee Yun),양은익(Yang Eun Ik),박해균(Park Hae Geun) 대한토목학회 2009 대한토목학회논문집 A Vol.29 No.4A

이 연구의 목적은 교량바닥판 콘크리트에 발생하는 부등건조수축에 의한 균열특성을 파악하고, 그 제어방법을 제시하는데 있다. 건조수축균열은 콘크리트 내부의 수분확산계수의 영향을 크게 받으며, 수분확산계수는 콘크리트 내부에서의 수분이동 속도를 결정하는 주요인자이다. 수분확산계수와 더불어 콘크리트 표면의 표면계수와 외부의 상대습도는 콘크리트 내부에서 외부로의 수분이동에 영향을 미친다. 따라서 이 연구에서는 교량 바닥판의 부등건조수축에 의한 균열특성을 파악하기 위하여 세 가지 주요영향인자를 고려한 수치해석을 수행하였다. 수치해석 결과, 수분확산계수와 표면계수가 증가할수록 교량바닥판에서의 부등건조수축에 의한 균열발생시점이 빨라지며, 세 가지 요인 중에 바닥판 콘크리트의 부동건조수축에 의한 균열발생특성에 가장 큰 영향을 미치는 것은 외기습도인 것으로 나타났다. 이 연구결과를 분석한 결과, 교량바닥판 콘크리트의 시공시에 콘크리트 타설 후 표면보습이나 살수양생과 같이 외기습도를 증가시키는 것이 부등건조수축에 의한 균열제어에 가장 효과적인 것으로 판단되며, 콘크리트 재료적 측면의 균열저감방법으로 수분확산계수와 표면계수를 결정하는 콘크리트의 배합이나 재료특성을 적절히 선정함으로써 균열의 진전속도나 발생시점을 제어할 수 있을 것으로 판단된다. The purpose of this study is to provide the efficient method and guideline of controlling the cracking in bridge deck concrete due to differential drying shrinkage. Drying shrinkage cracking is mainly influenced by the moisture diffusion coefficient that determines moisture diffusion rate inside concrete structures. In addition to the diffusion coefficient, surface coefficient of concrete surface and relative humidity of ambient air simultaneously affect the moisture evaporation from concrete inside to external air outside. Within the framework of cracking shrinkage cracking mechanism, it is necessary to conceive the numerical analysis, which involves these three influencing factors to predict and control the shrinkage cracking of concrete. In this study, moisture diffusion and stress analysis corresponding to drying shrinkage on bridge deck are performed with consideration of diffusion coefficient, surface coefficient, and relative humidity of ambient air. From the numerical results, it is found that cracking behavior due to differential drying shrinkage of bridge deck concrete shows different feature according to three influencing factors and the methodology of controlling of drying shrinkage cracks can be suggested from this study.

양생조건에 따른 고강도 콘크리트의 건조수축 및 자기수축에 관한 실험연구

이영화,윤종문,김화중 대한건축학회 2003 대한건축학회 학술발표대회 논문집 - 계획계/구조계 Vol.23 No.2

High-strength concrete is used in high rise building effectively but it has cracks due to the autogenous shrinkage. Therefore we performed a variety of experiments to analyze the characteristic of the autogenous and drying shrinkage of High-Strength concrete with the temperature and humidity in curing conditions. We measured the length change rate of experimented objects using Contact-Guage Method in the concrete of water-cement ratio 30% with the change of temperature(10, 20, 30℃) and relative humidity(30, 60, 90%). In consequence, on the first, the higher humidity, the lower autogenus shrinkage and drying shrinkage. second, it has the lowest length change of autogenus shrinkage and drying shrinkage in case of 10 ℃, and it is no difference between 20℃ and 30℃ for the constant humidity of 60% test. On the third, the ratio of drying shrinkage to autogenus shrinkage is the highest in case of the 30℃ temperature and 90% of relative humidity.

판상-링형 및 아령형 구속수축시험에 의한 콘크리트의 수축균열특성 평가에 관한 연구

김규용(Kim Gyu-Young),박윤미(Park Yun-Mi),남정수(Nam Jeong-Soo),김영덕(Kim Young-Dock),김호동(Kim Ho-Dong),김무한(Kim Moo-Han) 대한건축학회 2008 大韓建築學會論文集 : 構造系 Vol.24 No.10

Recently because of the lack of natural aggregate, crush saggregate is used. But it is apt to develop initial shrinkage crack and shrinkage crack by plastic and dry shrinkage. so to reduce crack, various attempt like mixing aggregage and reinforcing fiber is doing. However, the basic researches about the quantitative evaluation for concrete's shrinkage crack is lacking. Currently, method of test for drying shrinkage cracking of restrained concrete is to used to evaluate shrinkage in domestic. This study is trying to perform plat-ring restrained shrinkage test as well as method of test for drying shrinkage cracking of restrained concrete through a sort of mixing factors. As a result of experiment, crack point was discovered when using crush aggreage and unit water is high in plat-ring test. And reinforced fiber did not affect at crack initiation time in test for drying shrinkage cracking of restrained concrete.

재유화형 분말수지 출입 폴리머 시멘트 모르타르의 건조수축 및 강도특성

연규석,주명기,이현종,김성기,이지원,Yeon, Kyu-Seok,Joo, Myung-Ki,Lee, Hyun-Jong,Jin, Xing-Qi,Lee, Chi-Won 한국농공학회 2006 한국농공학회논문집 Vol.48 No.1

This study was conducted to investigate experimentally the drying shrinkage and the strength properties of redispersible SBR and PAE powder-modified mortars. Polymer-cement ratio, content of shrinkage-reducing agent and antifoamer content were manipulated as the experimental variables. The peculiarity of this study is to obtain a high early-age strength by using the portland cement and alumina cement with the ratio of 8 : 2. Until 7 days of age, the drying shrinkage remarkably increased up to $1\~2\times10^{-4}$, while it tended to decrease as the ratio of polymer to cement ratio and the content of shrinkage-reducing agent increased. Polymer-cement ratio was effective in improving the flexural, tensile and adhesive strengths: As the ratio increased, the strengths correspondingly increased. The flexural strength was in the range of $7\~11$ MPa, the tensile strength was $3.5\~5$ MPa and the adhesive strength was $1.2\~3.9$ MPa. On the other hand, the compressive strength tended to decrease as the polymer-cement ratio increased, and it was in the range of $23\~39$ MPa. All strengths, flexural, tensile, adhesive and compressive strengths, decreased as the content of powder shrinkage-reducing agent increased. It turned out that the polymer-cement ratio influenced more on the behavior of drying shrinkage and the properties of strength than the powder shrinkage-reducing agent did.

라텍스개질 콘크리트의 물-시멘트비에 따른 건조수축 특성

정원경,김성환,김동호,이주형,이봉학 江原大學校 産業技術硏究所 2002 産業技術硏究 Vol.22 No.A

Drying shrinkage cracking which may be caused by the relatively large specific suface is a matter of grave concern for latex modified concrete(LMC) overlay and rapid-setting cement latex modified concrete(RSLMC) overlay. LMC and RSLMC were studied for field applications very actively in terms of strength and durability in Korea. However, there were no considerations in drying shrinkage. Therefore, the purpose of this dissertation was to study the drying shrinkage properties of LMC and RSLMC with the main experimental variables such as cement types(ordinary portland cement, rapid setting cement), water-cement ratios and curing days at a same controlled environment of 60% of relative humidity and 20℃ of temperature. The drying shrinkage for specimens was measured with a digital dial gauge of Demec. The test results showed that the drying shrinkage of LMC and RSLMC were considerably lower with low water-cement ratio, respectively. This might be attributed to the interlocking of hydrated cement and aggregates by a film of latex particles, water retention due to hydrophobic, and colloidal properties of the latexes resulting in reduced water evaporation.