• Title/Summary/Keyword: early strength

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A Study on Early Strength Estimation of High-strength Concrete Using Non-sintering Cement (NSC) (비소성시멘트를 사용한 고강도 콘크리트의 조기강도 추정 연구)

  • Kim, Han-Sik;Lim, Sang-Jun;Kang, In-Seuk;Park, Moo-Young;Mun, Kyung-Ju;Jung, Sang-Jin
    • Proceedings of the Korea Concrete Institute Conference
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    • 2006.05b
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    • pp.609-612
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    • 2006
  • The quality of the concrete compression strength can be determined after the passage of 28 days, but if any defect is found the quality of concrete after that length of time, there can be serious problems in dismantling and repair. Thus, in response to the use of concrete using non sintering cement (NSC), the present study purposed to propose a method of managing the strength of high strength concrete using NSC in comparison with high strength concrete using ordinary Portland cement (OPC) through early strength estimation using microwave, which enables the quick estimation of the strength of high strength concrete using NSC.

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An Experimental Study on the Early Strength Development Properties of Concrete According to Curing Condition and Used Materials (사용재료 및 양생조건에 따른 콘크리트의 조기강도발현 특성에 관한 실험적 연구)

  • Lee, Sang-Soo;Song, Ha-Young;Lee, Ji-Hwan
    • Journal of the Korea Concrete Institute
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    • v.20 no.6
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    • pp.721-729
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    • 2008
  • The purpose of this study is to investigate the engineering properties of concrete for the early strength development. As a result of reviewing it by establishing each experimental factor and level, the cement had more excellent quality performance in CHC and HESPC than OPC. This study has shown that the PC series admixture was more excellent in side of elapsed time (aging) and early strength development than PNS series admixture. In addition, there was much difference according to the curing temperature, but the early strength development showed the considerable vulnerability in curing temperature below $12^{\circ}C$. To satisfy the strength requirements of 5 MPa/18 hr this study has shown that it needed the curing temperature over $17^{\circ}C$ to the minimum in OPC, over $14^{\circ}C$ in CHC, and over $11^{\circ}C$ in HESPC. On the other hand, as to the strength properties according to W/C, the less W/C was, the more strength development was excellent. If this study is to be used in construction filed on a basis of this result, this researcher is considered as possible of the economic execution of construction by advancing the early strength and by the reduction of construction cost according to shortening construction duration.

Factors Influencing Fear of Falling among Women in the Early Phase of Old Age by Assessing Level of Hand Grip Strength (노년전기 여성의 악력 수준에 따른 낙상 두려움의 영향 요인)

  • Noh, Jun Hee;Lim, Eun Ju
    • Journal of Korean Academic Society of Home Health Care Nursing
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    • v.25 no.1
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    • pp.96-104
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    • 2018
  • Purpose: This study compared factors related to fear of falling among women in the early phase of old age based on hand grip strength. Methods: Researchers obtained data of 1,071 women who had participated in the 4th Korean Longitudinal Study of Aging. Data were analyzed using multiple regression analysis. Results: In both groups, fear of falling was positively correlated with falling experience within two years, osteoarthritis-related leg pain, depression, and instrumental daily life abilities; however, self-rated health was negatively correlated. In the low hand grip strength group, self-rated health, osteoarthritis-related leg pain, and hand grip strength accounted for 21.3% of the variance regarding fear of falling. In the normal hand grip strength group, age, self-rated health, fall experience within two years, osteoarthritis-related leg pain, and depression significantly accounted for 16.6% of the variance regarding fear of falling. Conclusion: In applying interventions to prevent falling in women in the early phase of old age, health care workers must verify if women have low hand grip strength and determine whether to focus on fitness improvement through exercise interventions or consider psychological interventions for depression.

The Specification of OPC and Micro Cement using the Admixture (보통포틀랜드 시멘트와 초미립자 시멘트의 혼화재료 혼입시 특성)

  • Kim, Deuck-Mo;Lee, Wha-Young;Park, Won-Chun;Mun, Kyung-Ju;Soh, Seung-Young;Soh, Yang-Seob
    • Proceedings of the Korea Concrete Institute Conference
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    • 2008.04a
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    • pp.905-908
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    • 2008
  • The existing concrete using ordinary portland cement has difficult in earth strength. so our study proceeded in using the micro cement. the result of experiment is follow that strength of micro cement was hard better than ordinary portland cement in early strength but flow of ordinary portland cement was better than micro cement. when OPC and MC mixed by fly-ash, flow degree is increased because of ball baring. fly-ash type wicked in early strength but flyash type hard than 28days strength of OPC. flow of GBFS is decreased, early strength is increased. when fly-ash mixed in MC, it was wicked strength.

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3-Dimensional numerical analysis on support performance of early-high-strength shotcrete (3차원 수치해석을 이용한 조기고강도 숏크리트 지보성능 분석)

  • Kim, Jong-Uk;Kim, Jung-Joo;Cho, Young-Jae;Yoo, Han-Kyu
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.16 no.5
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    • pp.459-470
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    • 2014
  • Now-a-days, the trend in constructing tunnels is to build more deeper, more longer tunnels of greater cross-sections. That's why, the demand of "Early-high-strength shotcrete" is very high because of their advantage of attaining higher strength immediately after excavation, which controls the ground subsidence. So, this study reveals the supporting phenomena of early-high-strength shotcrete, using three-dimensional numerical analysis. The crux of this study can be applied practically in construction sites also. Support Performance of two different qualities of shotcrete was checked out, by keeping the general shotcrete's thickness constant and comparing it with early-high-strength shotcrete's thickness decreasing it gradually in five steps, and analysing/comparing the support performance in all cases. Effect of using early-high-strength shotcrete was analysed to save the cost of steel sets, which are widely used for supporting the ground before the hardening of general shotcrete. The results of numerical analysis on the performance of early-high-strength shotcrete show that, it behaves more effectively under worse ground conditions and it can support the ground more conveniently than steel sets, before the shotcrete is hardened.

Experimental Study of Freezing Characteristics and Antifreezing Method of Liquid Additive for Early Strength (액상형 조강제의 동결특성 및 동결방지 방안에 관한 실험적 고찰)

  • Lee, Mun-Hwan;Ryu, Deug-Hyun
    • Journal of the Korea Concrete Institute
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    • v.19 no.5
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    • pp.647-653
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    • 2007
  • In ready mixed concrete factory, in case of using the high molecular additive in winter especially the liquid additive for the early strength, it is required to check the stability. In this research, the freezing and gelling characteristics of the liquid additive for the early strength is reviewed, the material and mechanical solution are proposed to that the practical quality control method will be suggested. As the result, the Freezing temperature of the liquid additive for the early strength is $-11.8^{\circ}C$, and it is the lower than the temperature at which the strength is shown. By making with sodium silicate of $37{\pm}0.5%$ designed by $SiO_2\;and\;Na_2O$ in 0.31 of mol ratio, it minimizes the gelling at the lower temperature. On the other hand, facilities for storing and supplying the material should be set at $40^{\circ}C$ so the temperature distribution is well spreaded for practical operation.

Effect of ages and season temperatures on bi-surface shear behavior of HESUHPC-NSC composite

  • Yang Zhang;Yanping Zhu;Pengfei Ma;Shuilong He;Xudong Shao
    • Advances in concrete construction
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    • v.15 no.6
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    • pp.359-376
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    • 2023
  • Ultra-high-performance concrete (UHPC) has become an attractive cast-in-place repairing material for existing engineering structures. The present study aims to investigate age-dependent high-early-strength UHPC (HESUHPC) material properties (i.e., compressive strength, elastic modulus, flexural strength, and tensile strength) as well as interfacial shear properties of HESUHPC-normal strength concrete (NSC) composites cured at different season temperatures (i.e., summer, autumn, and winter). The typical temperatures were kept for at least seven days in different seasons from weather forecasting to guarantee an approximately consistent curing and testing condition (i.e., temperature and relative humidity) for specimens at different ages. The HESUHPC material properties are tested through standardized testing methods, and the interfacial bond performance is tested through a bi-surface shear testing method. The test results quantify the positive development of HESUHPC material properties at the early age, and the increasing amplitude decreases from summer to winter. Three-day mechanical properties in winter (with the lowest curing temperature) still gain more than 60% of the 28-day mechanical properties, and the impact of season temperatures becomes small at the later age. The HESUHPC shrinkage mainly occurs at the early age, and the final shrinkage value is not significant. The HESUHPC-NSC interface exhibits sound shear performance, the interface in most specimens does not fail, and most interfacial shear strengths are higher than the NSC-NSC composite. The HESUHPC-NSC composites at the shear failure do not exhibit a large relative slip and present a significant brittleness at the failure. The typical failures are characterized by thin-layer NSC debonding near the interface, and NSC pure shear failure. Two load-slip development patterns, and two types of main crack location are identified for the HESUHPC-NSC composites tested in different ages and seasons. In addition, shear capacity of the HESUHPC-NSC composite develops rapidly at the early age, and the increasing amplitude decreases as the season temperature decreases. This study will promote the HESUHPC application in practical engineering as a cast-in-place repairing material subjected to different natural environments.

Study on the qualities & application of Super High Early Strength -Self Compact Concrete using Type III Cement for productabilities- (조강시멘트를 이용한 속경성 자기충전 콘크리트의 배합인자별 품질특성 및 활용에 관한 연구)

  • 엄태선;임채용;유재상;이종열
    • Proceedings of the Korea Concrete Institute Conference
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    • 2002.10a
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    • pp.573-578
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    • 2002
  • We carried out the feasibility study of super early self compacting concrete having the characteristics of 1 day demoulding without steam curing, high flowable concrete with self compacting, high strength and high durability etc. Here, We test and selected by several methods using high early cement with and without admixtures for the condition of super early strength self compacting concrete's manufacture (SSCC). We sucessed to meet at the goal of SSCC with 30∼35N/㎟ in 1 day, without steam curing and with slump flow about 60-65cm and suggest various concrete products to apply the developed SSCC for practical use in factory and in site place

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Crack Prevention of Very-Early Strength Latex-Modified Concrete (초속경 라텍스개질 콘크리트의 균열 억제방안)

  • Lee, Bong-Hak;Choi, Pan-Gil
    • Journal of Industrial Technology
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    • v.28 no.A
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    • pp.89-96
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    • 2008
  • An increase in the amount of cracking in repaired concrete bridge decks using VES-LMC(Very Early Strength - Latex Modified Concrete ; below VES-LMC) has been noticed by Yun et al(1). Literature indicates that indeed many concrete bridge decks develop transverse cracking, most developing at early ages(3~7 days), many right after construction. The purpose of this study was to establish prevention of map, transverse and longitudinal cracking in VES-LMC and to provide a control methods for minimizing the occurrence of cracks. The proposed prevention against map and transverse cracking was verified by field applications. VES cement was modified, the unit cement contents was reduced into $360kg/m^3$ from $390kg/m^3$, the maximum size of coarse aggregate was increase into 19mm from 13mm, wire mesh and steel fibers were incorporated in concrete mixture. A series of variable combinations were attempted. As a results, the proposed prevention against map and transverse cracking was verified because no crack were occurred until 90 days after overlay.

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A Study on the Early Quality Improvement of Concrete Incorporating CSA Admixture (CSA에 의한 콘크리트의 초기품질향상에 관한 연구)

  • Pei Chang-Chun;Lee Gun-Cheol;Park Jae Myoung;Lee Se Hyoen;Han Cheon-Goo
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2005.05a
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    • pp.25-28
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    • 2005
  • This study shows the early quality improvement of concrete with calcium sulfa aluminate(CSA). For the properties of slump, plain concrete incorporating BS $35\%$ and UP $15\%$ resulted in high fluidity compared with OPC without any admixture. As displacement ratio of CSA increased. the fluidity decreased. The fluidity also declined with setting time. Increase of incorporation ratio of CSA declined bleeding and accelerated setting time. Importantly, using more CSA helped to improve early compressive strength and decrease drying shrinkage. In term of water curing, drying shrinkage hardly ever occurred.

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