• Title/Summary/Keyword: Cracking

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Experimental Study on the Shrinkage Properties and Cracking Potential of High Strength Concrete Containing Industrial By-Products for Nuclear Power Plant Concrete

  • Kim, Baek-Joong;Yi, Chongku
    • Nuclear Engineering and Technology
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    • v.49 no.1
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    • pp.224-233
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    • 2017
  • In Korea, attempts have been made to develop high strength concrete for the safety and design life improvement of nuclear power plants. In this study, the cracking potentials of nuclear power plant-high strength concretes (NPP-HSCs) containing industrial by-products with W/B 0.34 and W/B 0.28, which are being reviewed for their application in the construction of containment structures, were evaluated through autogenous shrinkage, unrestrained drying shrinkage, and restrained drying shrinkage experiments. The cracking potentials of the NPP-HSCs with W/B 0.34 and W/B 0.28 were in the order of 0.34FA25 > 0.34FA25BFS25 > 0.34BFS50 > 0.34BFS65SF5 and 0.28FA25SF5 >> 0.28BFS65SF5 > 0.28BFS45SF5 > 0.28 FA20BFS25SF5, respectively. The cracking potentials of the seven mix proportions excluding 0.28FA25SF5 were lower than that of the existing nuclear power plant concrete; thus, the durability of a nuclear power plant against shrinkage cracking could be improved by applying the seven mix proportions with low cracking potentials.

Cracking Control of Concrete Deck in Steel-Concrete Composite Bridges (강합성 교량의 바닥판 콘크리트 균열관리)

  • 박해균;이명섭;안병제;곽효경;서영재
    • Proceedings of the Korea Concrete Institute Conference
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    • 2001.11a
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    • pp.355-362
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    • 2001
  • This study deals with cracking control of concrete deck in steel-concrete composite bridges according to the concrete slab casting sequences. In correlation studies between casting sequences, time dependent effects of concrete creep and shrinkage are implemented in the analytical model. Finally, the methods of cracking control in terms of concrete slump and relative humidity are suggested to prevent early transverse cracking of concrete slab.

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Thermal Crack Control of Mass Concrete by Concrete Placing Height and Curing Method (매스콘크리트의 타설높이 및 양생조건에 따른 온도균열 저감 방안에 관한 연구)

  • 민병소;신길수;김대권;이현희;신성우;이광수
    • Proceedings of the Korea Concrete Institute Conference
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    • 2001.11a
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    • pp.369-376
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    • 2001
  • As many studies have performed to reduce thermal cracking in mass concrete, it is already prepared against thermal cracking, we can find many plans against thermal cracking in several reference book. But it needs practical guidelines to be available in construction site. In this study to establish control method of thermal cracking in mass concrete, tests which have factors of placing thickness and curing method of concrete are performed.

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Cracking in reinforced concrete flexural members - A reliability model

  • Rao, K. Balaji;Rao, T.V.S.R. Appa
    • Structural Engineering and Mechanics
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    • v.7 no.3
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    • pp.303-318
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    • 1999
  • Cracking of reinforced concrete flexural members is a highly random phenomenon. In this paper reliability models are presented to determine the probabilities of failure of flexural members against the limit states of first crack and maximum crackwidth. The models proposed take into account the mechanism of cracking. Based on the reliability models discussed, Eqs. (8) and (9) useful in the reliability-based design of flexural members are presented.

Occurrence of Micro-cracking According to Bagging Paper in 'Mansoo' Pear Fruits (과실 봉지에 따른 배 '만수' 품종의 미세 열과 발생)

  • Choi, Jin-Ho;Yim, Sun-Hee;Kim, Sung-Jong;Lee, Han-Chan;Kwon, YongHee
    • Horticultural Science & Technology
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    • v.33 no.4
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    • pp.479-485
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    • 2015
  • This study was conducted to study the factors inducing micro-cracking and determine proper practices to reduce its occurrence in 'Mansoo' pear fruits. Micro-cracking was observed on ripe fruits. Occurrence of micro-cracking was closely related to sun duration time in August. Micro-cracking occurred severely with shorter sun duration, but weakly with longer sun duration and continuous sunlight. Micro-cracking fruits occurred more frequently in trees with a pergola training system than in those with Y-trellis, but there was no difference between the irrigated and non-irrigated groups. While no micro-cracking was observed without fruit bagging, micro-cracking occurred in fruits with black and yellow outer paper bagging at rates of 62.2 and 17.3%, respectively. Our results suggest that the light condition was the most important cause of micro-cracking because the occurrence of micro-cracking in 'Mansoo' fruits was affected by factors including sun duration, trellis system and fruit bag color. We suggested that micro-cracking could be reduced in 'Mansoo' fruit by optimizing the light conditions with the proper trellis system, bagging color and summer pruning.

Analytical model of corrosion-induced cracking of concrete considering the stiffness of reinforcement

  • Bhargava, Kapilesh;Ghosh, A.K.;Mori, Yasuhiro;Ramanujam, S.
    • Structural Engineering and Mechanics
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    • v.16 no.6
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    • pp.749-769
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    • 2003
  • The structural deterioration of concrete structures due to reinforcement corrosion is a major worldwide problem. Service life of the age-degraded concrete structures is governed by the protective action provided by the cover concrete against the susceptibility of the reinforcement to the corrosive environment. The corrosion of steel would result in the various corrosion products, which depending on the level of the oxidation may have much greater volume than the original iron that gets consumed by the process of corrosion. This volume expansion would be responsible for exerting the expansive radial pressure at the steel-concrete interface resulting in the development of hoop tensile stresses in the surrounding cover concrete. Once the maximum hoop tensile stress exceeds the tensile strength of the concrete, cracking of cover concrete would take place. The cracking begins at the steel-concrete interface and propagates outwards and eventually resulting in the through cracking of the cover concrete. The cover cracking would indicate the loss of the service life for the corrosion-affected structures. In the present paper, analytical models have been developed considering the residual strength of the cracked concrete and the stiffness provided by the combination of the reinforcement and expansive corrosion products. The problem is modeled as a boundary value problem and the governing equations are expressed in terms of the radial displacement. The analytical solutions are presented considering a simple 2-zone model for the cover concrete viz. cracked or uncracked. A sensitivity analysis has also been carried out to show the influence of the various parameters of the proposed models. The time to cover cracking is found to be function of initial material properties of the cover concrete and reinforcement plus corrosion products combine, type of rust products, rate of corrosion and the residual strength of the cover concrete. The calculated cracking times are correlated against the published experimental and analytical reference data.

Study on the Crack Control Effect of Moist Curing Equipment in Side Wall of Building (습윤양생 장치를 이용한 아파트 측벽 균열제어에 관한 연구)

  • Kim, Dae-Geon;Lee, Dong-Woon
    • Journal of the Korea Institute of Building Construction
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    • v.17 no.2
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    • pp.127-134
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    • 2017
  • In this study, moist curing equipment was used in the exist gang-form system. By achieving sufficient spray curing, the quality of the concrete was improved and the cracking occurred in building's side wall was decreased. The following results could be made as the conclusion. For the compressive strength, all zones showed the similar results. Comparing with the zone without using moist curing equipment, the zone used moist curing equipment showed higher rebound hardness results. For the cracking, the zone utilized moist curing equipment showed the cracking averaged as 6.6 m and the zone without using moist curing equipment showed the cracking averaged as 10.3m. The effectof reducing cracking by utilizing moist curing equipment is about 36 %. Using moist curing equipment is considered as a good solution to reduce the cracking in the structure. Considering all the factors analysed, using moist curing equipment improved the quality of the concrete and decreased the cracking. When this equipment was used in the construction site, it is expected that the construction periodcan be shrunk and the ratio of defect caused by drying shrinkage can be decreased. In this research conditions, The 0.3mm sized moist curing equipment provided the most desirable results on concrete quality and preventing cracking.

A Study of Weld Fusion Zone Phenomena in Austenitic Stainless Steels(2) - Effects of Nitrogen on Microstructural Evolution and Hot Cracking Susceptibility GTA Welds in STS 304 - (오스테나이트계 스테인리스강 용접부의 금속학적 현상에 관한 연구(2) - STS 304 용접부 조직특성 및 고온균열 감수성에 미치는 질소의 영향 -)

  • 이종섭;김숙환
    • Journal of Welding and Joining
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    • v.18 no.1
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    • pp.59-69
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    • 2000
  • The purpose of the present study was to investigate weld metallurgical phenomena such as primary solidification mode, microstructural evolution and hot cracking susceptibility in nitrogen-bearing austenitic stainless steel GTA welds. Eight experimental heats varying nitrogen content from 0.007 to 0.23 wt.% were used in this study. Autogenous GTA welding was performed on weld coupons and the primary solidification mode and their microstructural characteristics were investigated from the fusion welds. Varestraint test was employed to evaluate the solidification cracking susceptibility of the heats and TCL(Total Crack Length) was used as cracking susceptibility index. The solidification mode shifted from primary ferrite to primary austenite with an increase in nitrogen content. Retained delta ferrite exhibited a variety of morphology as nitrogen content varied. The weld fusion zone exhibited duplex structure(austenite+ferrite) at nitrogen contents less than 0.10 wt.% but fully austenitic structure at nitrogen contents more than 0.20 wt.%. The weld fusion zone in alloys with about 0.15 wt.% nitrogen experienced primary austenite + primary ferrite solidification (mode AF) and contained delta ferrite less than 1% at room temperature. Regarding to solidification cracking susceptibility, the welds with fully austenitic structure exhibited high cracking susceptibility while those with duplex structure low susceptibility. The cracking susceptibility increased slowly with an increase in nitrogen content up to 0.20 wt.% but sharply as nitrogen content exceeded 0.20 wt.%, which was attributed to solidification mode shift fro primary ferrite to primary austenite single phase solidification.

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Determination of Thermal Cracking Index of Internal Restricted Mass Concrete Using a Numerical Analysis (수치분석을 통한 내부구속 매스콘크리트의 온도균열지수 결정)

  • Seo, Ki-Young;Kim, Hee-Sung;Jin, Chi-Sub
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.11 no.1
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    • pp.57-67
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    • 2007
  • The service life of concrete structure is to a great extent influenced by crack developed at early ages of concrete material. Especially, hydration heat is a main cause of thermal cracking at mass concrete structures. The thermal cracking of massive structure is analyzed of the thermal cracking index which was presented Concrete Standard Specifications. The thesis analyzed the thermal cracking index which considered various variable (cement type, height of casting, curing condition, concrete mixing temperature, the unit cement content) at internal restricted mass concrete. The analysis result is denoted increase and decrease rate of thermal cracking index whenever the variables change. The results is helped to understand thermal cracking every time structures is designed and constructed. And I think that it is useful economic and stable design of mass concrete structures.

An Analytical Method for the Evaluation of Micro-cracking in Concrete Shrinkage Induced (콘크리트의 수축으로 인한 미세균열 발생 평가를 위한 해석적 기법)

  • Song, Young-Chul;Kim, Do-Gyeum;Moon, Jae-Heum
    • Journal of the Korea Concrete Institute
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    • v.22 no.1
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    • pp.69-76
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    • 2010
  • The majority of research that has been performed on cracking potential of concrete by shrinkage has assumed that concrete acts as a homogeneous material. However, with this approach, it is not able to evaluate the micro-cracking behavior in concrete due to autogenous shrinkage under unrestrained boundary condition (free boundary condition) nor to understand the cracking behavior properly because of the heterogeneous nature of concrete. To better understand the micro-cracking behavior of concrete induced by autogenous shrinkage, series of experiments were performed measuring the length change and acoustic emission energy. As an analytical approach, this research uses an object oriented finite element analysis code (OOF code) to simulate the behavior of the concrete on a meso-scale. The concrete images used in the simulations were directly obtained from mortar samples. From the experiments and simulation results, it was able to better understand the micro-cracking behaviour of concrete due to shrinking of paste phase and internal restraint by aggregates.