• Title/Summary/Keyword: 탈형시기

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Characteristics of Compressive Strength of Concrete due to Form Curing Condition (거푸집 양생 조건에 따른 콘크리트의 압축강도 특성)

  • Kim, Kyoungnam;Park, Sangyeol;Moon, Kyoungtae;Shim, Jaeyong
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.38 no.1
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    • pp.19-28
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    • 2018
  • The time for form removal is an important factor for ensuring the safety and economical efficiency of concrete structures, because it affects the quality, period, and cost of construction. Although local specifications suggest the form curing time, there is a problem of low quality of concrete due to early removing of form. This is because they do not fully understand effect of curing condition, and they want to shorten construction period in the field. Therefore, this research evaluates the effect of curing condition according to the time for form removal by testing specimen. As a result, the concrete compressive strength at the age of 28 days decreased about 40% in the condition of form removal after 12 hours, while the strength in the condition of form removal after 28 days decreased about 7%. Finally, this paper suggests an estimating equation for the concrete compressive strength due to the time for form removal considering various curing temperatures as equivalent ages. The proposed equation can be used in the field for evaluating the strength after form removal.

Determination of Removal Time of the Forms with the Strength Development of High Strength Concrete at Early Age (고강도 콘크리트의 초기강도 발현에 따른 거푸집 탈형시기의 결정)

  • 김은호;김영진;한민철;신병철;한천구
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2003.05a
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    • pp.99-102
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    • 2003
  • This study discusses the determination of removal time of forms with early strength development in high strength concrete. According to the results, as W/B increases by 10%, the setting time is shortened by about 2 hours. The time when compressive strength of 8 MPa is gained is about 20 hours. Bond strength between form and concrete is highest around final setting time, but decreases drastically after that. Amount of concrete sticking on the form is large before setting, but after that, it is little. The rebound value of P type schmidt hammer is measured faster by 2-3 hours than compressive strength. It is also confirmed that the removal of forms is possible when the rebound value of P type schmidt hammer is more than 34

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Field Application of High Strength Concrete by Cement Types Using Maturity (적산온도를 이용한 시멘트 종류별 고강도 콘크리트의 현장 적용성)

  • Kim, Dong Baek
    • Journal of the Society of Disaster Information
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    • v.16 no.3
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    • pp.472-478
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    • 2020
  • Purpose: The purpose of the study is to help economic and safe construction by accurately predicting the initial strength of high-strength concrete (70MPa) for each type of cement, securing reliability of concrete quality, and drawing accurately the timing of form deformed, tensioning time of PS concrete, and openning of traffic after road repair with maturity. Method: Calculate the maturity by measuring the hydration heat with cement type for each age, and measure the strength of concrete with age to predict the strength corresponding to the any maturity. Result: In estimating the time required for traffic opening in road repair, ASTM C1074 was theoretically estimated at 16.4 hours for high-strength concrete, but in this study, maturity was calculated at 307, 14.4 hours for OPC and maturity at 2700, 34 hours for LHPC and maturity 200, 8 hours for ESPC. Conclusion: The timing of form deformed of structures using high-strength concrete and the opening of traffic of road repair may be much faster than in the case of concrete using OPC below the design basis strength 40MPa applied by ACI Committee 347.

ALC(Autoclaved Lightweight Concrete) Hardness Prediction by Multiple Regression Analysis (다중회귀분석을 이용한 ALC 경도예측에 관한 연구)

  • Kim, Kwang-Soo;Baek, Seung-Hoon;Chung, Soon-Suk
    • Asia-Pacific Journal of Business Venturing and Entrepreneurship
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    • v.7 no.2
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    • pp.101-111
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    • 2012
  • In the ALC(Autoclaved lightweight concrete) manufacturing process, if the pre-cured semi-cake is removed after proper time is passed, it will be hard to retain the moisture and be easily cracked. Therefore, in this research, we took the research by multiple regression analysis to find relationship between variables for the prediction the hardness that is the control standard of the removal time. We study the relationship between Independent variables such as the V/T(Vibration Time), V/T movement, expansion height, curing time, placing temperature, Rising and C/S ratio and the Dependent variables, the hardness by multiple regression analysis. In this study, first, we calculated regression equation by the regression analysis, then we tried phased regression analysis, best subset regression analysis and residual analysis. At last, we could verify curing time, placing temperature, Rising and C/S ratio influence to the hardness by the estimated regression equation.

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Development of Early-Strength of High-Strength Concrete According to Curing Temperature for Application of System Form (시스템 거푸집 적용을 위한 고강도 콘크리트의 양생온도별 조기강도 발현성상)

  • 김무한;이승훈;강석표;길배수;주지현
    • Journal of the Korea Concrete Institute
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    • v.13 no.6
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    • pp.536-543
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    • 2001
  • Nowadays, with high-stoned and large-sized of structures, high-strength concrete is applicable to various methods. When high-strength concrete is used jointly with system form, seizing on the development of compressive strength at early age is very important in aspect of construction process. Because system form is stripped more faster than ordinary form. But, we have little data of compressive strength before system-form is stripped, and it isn't yet established that decision criterion of the time when system-form is stripped. So this paper deals with the development of compressive strength at early age before system-form is stripped. In this study, the experimental results indicate the boundary of curing temperature and mixing factor that is able to get needful early-strength in the application of slip-form method, and curing temperature must be kept over 15 degrees in winter season.

Determination of Removal Time of the Side Form in High Strength Concrete (고강도콘크리트 시공시 측면 거푸집 탈형시기의 결정)

  • Han Cheon-Goo;Han Min-Cheol
    • Journal of the Korea Concrete Institute
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    • v.16 no.3 s.81
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    • pp.327-334
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    • 2004
  • In this paper, method for the determination of removal time of the side forms in high strength concrete are discussed using the estimation model of compressive strength development, the development of bond strength and rebound number of P type Schmidt hammer in order to review the validity of existing regulation as to side form removal and offer effective quality control method. According to the results, as W/B increases by $10\%$, the setting time is shortened by about 2 hours. In the scope of the paper, required time to gain 8MPa of compressive strength is determined about 17 ${\~}$20 hours of age and $21{\~}25^{\circ}D{\cdot}D$ of maturity. Bond strength between form and concrete shows the highest value around final setting time, but decreases drastically after that. Amount of concrete sticking on the form is large before setting completed, but after that, its amount shows decline tendency. The rebound value test with P type schmidt hammer can be started faster by 2${\~}$3 hours than compressive strength test. It is also confirmed that the removal of forms is possible when the rebound value of P type schmidt hammer is more than 32. It is found from the results that existing regulation regarding removal time of the side form of high strength concrete provided in KCI needs no revision because required time to gain the strength provided in KCI has no adverse effect on strength development at early age and surface condition during stripping the side form. Effective procedure to decide the removal time of side form can be performed by applying P type Schmidt hammer.

Investigation on the Validities of Removal Time of the Forms Considering Rebound Number of P Type Shumidt Hammer (P형 슈미트 햄머의 반발도를 이용한 거푸집 탈형시기의 결정에 관한 타당성 검토)

  • 전충근;김상우;신병호;황인성;신병철;한천구
    • Proceedings of the Korea Concrete Institute Conference
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    • 2001.11a
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    • pp.909-912
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    • 2001
  • This paper presents the validities of the removal time of side forms considering the relationship between rebound number of P type schmidt hammer and compressive strength. According to test results, compressive strength of 40% of W/C at 12 hours shows 16kgf/$cm^{2}$ and 50% of W/C at 15 hours, 13kgf/$cm^{2}$. Rebound number at 9 hours after casting shows 13 and 9 (W/C 40% and W/C 50%). According to the regression analysis, rebound number of P type schmidt hammer to gain 50kgf/$cm^{2}$ of is estimated 20.1. It is thought that desirable rebound number of P type schmidt hammer to gain 50kgf/$cm^{2}$ is determined 25 considering safety factor.

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A Study on the Properties of Early Strength with the Kind and Replacement Ratio of Mineral Admixture (혼화재 종류 및 치환율 변화에 따른 조기강도 특성에 관한 연구)

  • Shin, Jae-Kyung;Choi, Jin-Man;Jeong, Yong;Kim, In-Ho;Choi, Hee-Ju;Park, Cheol
    • Proceedings of the Korea Concrete Institute Conference
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    • 2009.05a
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    • pp.209-210
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    • 2009
  • In constuction work, the early compressive strength in reference to the demolding time of side forms is significant on reducing the construction time and improving the economical efficiency. Therefore, this study is investigated the effect of the kind and replacement ratio of mineral admixture on the development of early strength.

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Study on the Strength Development of Fly ash Replace Concrete by a In-situ Temperature System (온도추종 양생 장치에 의한 플라이애쉬 치환 콘크리트의 강도 발현 성상)

  • Lee, Gun-Cheol;Yoon, seung-joe;Lee, Gun-Young;Choi, Jung-Gu;Kim, Kyoung-Min
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2014.05a
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    • pp.126-127
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    • 2014
  • At construction sites, due to the reason of inconvenience and difficulties of producing and using curing equipment and when it comes to measuring compression strength of the actual structure, strength of structure concrete according to general standards which are suggested in concrete standard specification are assessed. However, this method does not consider various variables of the sites such as kinds concretes and sizes of frame works so that it is not easy to measure proper curing period and strength. Thus, this study reviews description of strength development according to In-situ temperature system and analyzes and compares properties of strength development of the existing curing methods such as sealing curing so that it provides basic materials for period of removal of molds.

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Evaluation of Field Application on the Prediction Method of Early-age Strength of Early Concrete for Construction Work Period Reduction (공기단축 조강콘크리트의 조기강도 예측기술의 현장적용성 평가)

  • Lee, Woong-Jong;Keum, Kyoung-Hun;Lee, Jae-Hyun;Jung, Yang-Hee;Kim, Yong-Ro
    • Proceedings of the Korea Concrete Institute Conference
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    • 2010.05a
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    • pp.443-444
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    • 2010
  • In this study, It is confirmed the validity for determination of the form removal time, utilizing prediction expression for early-stage strength which depended on the variation of curing history for early strength concrete which be passible to construction work period reduction, in apartment.

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