• Title, Summary, Keyword: Shrinkage

Search Result 3,010, Processing Time 0.046 seconds

Differential Drying Shrinkage and Autogenous Shrinkage of Concrete at Early Ages (초기재령 콘크리트의 부등건조수축과 자기수축에 관한 연구)

  • 김진근;이칠성
    • Proceedings of the Korea Concrete Institute Conference
    • /
    • /
    • pp.309-314
    • /
    • 1998
  • The moisture diffusion and self-desiccation cause the differential drying shrinkage and autogenous shrinkage at early ages, respecitvely. Thus total shrinkage strain includes the differential drying shrinkage and self-desiccation shrinkage. Thus in this study the shrinkage strain was measured at various positions in the exposed concrete and in the sealed concrete the self-desiccation shrinkage was measured. In low-strength concrete, the differential drying shrinkage increases very rapidly, but self-desiccation shrinkage is very small. But high-strength concrete shows the reverse result. And the analytical results for differential drying shrinkage were in good agreement with the test results.

  • PDF

A Study on the Creep and Autogenous Shrinkage of High Performance Concrete with Expansive Additive and Shrinkage Reducing Admixtures at Early Age

  • Park, Sun-Gyu;Noguchi, Takafumi;Kim, Moo-Han
    • International Journal of Concrete Structures and Materials
    • /
    • v.18 no.2E
    • /
    • pp.73-77
    • /
    • 2006
  • This paper shows a study of the efficiency of expansive additive and shrinkage reducing admixture in controlling restrained shrinkage cracking of high performance concrete at early age. Free autogenous shrinkage test of $100{\times}100{\times}400mm$ concrete specimens and simulated completely-restrained test with VRTM(variable restraint testing machine) were performed. Creep and autogenous shrinkage of high-performance concrete with and without expansive additive and shrinkage reducing admixture were investigated by experiments that provided data on free autogenous shrinkage and restrained shrinkage. The results showed that the addition of expansive additive and shrinkage reducing admixture effectively reduced autogenous shrinkage and tensile stress in the restrained conditions. Also, it was found that the shrinkage stress was relaxed by 90% in high-performance concrete with and without expansive additive and shrinkage reducing admixtures at early age.

An Experimental Study on Shrinkage of High Strength Concrete with Mineral Admixture (혼화재 사용에 따른 고강도 콘크리트의 수축에 관한 실험적 연구)

  • Lee, Young-Jae
    • Journal of the Korean Society of Industry Convergence
    • /
    • v.13 no.2
    • /
    • pp.99-106
    • /
    • 2010
  • The effects of additive and shrinkage reducing agent on the drying and autogenous shrinkage of high strength concrete are investigated in this study. As results, when the ratio of W/B(low water to binder ratio) increase, the compressive strength is decreased. Comparing with PC(portland cement) concrete, the strength is 2.8%, 3.2% and 3.8% lower respectively than that of PC when concrete mixing ratio is 0.2%, 0.3% and 0.4% in 28 days curing. Drying shrinkage strain of PC concrete showed $-650{\times}10^{-6}$ in 91 days curing. When SR(shrinkage reducing agent) of 0.2%, 0.3% and 0.4% is mixed, the drying shrinkage strains are 21%, 34% and 41% lower than those of PC in 91 days curing. Autogenous shrinkage strain of PC concrete appeared $-480{\times}10^{-6}$ in 56 days curing. When SR of 0.2%, 0.3% and 0.4% is mixed, the autogenous drying shrinkage strain are 12.5%, 19.8% and 33.3% lower than those of PC in 56 days curing. In cases of using the mineral and shrinkage agent or only using a shrinkage reducing agent also appeared same reducing effects for drying shrinkage and autogenous shrinkage.

  • PDF

Effect of Expanding Admixture and Shrinkage Reducing Agent on the Shrinkage Reducing Properties of Ultra High Performance Cement Mortar (팽창재 및 수축저감제가 초고성능 시멘트 모르타르의 수축특성에 미치는 영향)

  • Han, Dong-Yeop;Yu, Myoung-Youl;Lee, Hyun-Soo
    • Proceedings of the Korea Concrete Institute Conference
    • /
    • /
    • pp.61-64
    • /
    • 2006
  • Comparing with traditional high performance concrete, ultra high performance concrete (UHPC) has the property of high-tenacity. However, drying shrinkage and autogenous shrinkage can be arisen as the major defect to UHPC. In this study, therefore, it was tested to reduce drying shrinkage and autogeneous shrinkage by adding expanding admixture (EA) and shrinkage reducing agent (SRA). As a result, for a case drying shrinkage, the shrinkage was decreased by 94% when EA was exchanged, and it was decreased by 64% when SRA was added. For the case of autogenous shrinkage, the mortar was expanded at early age and the shrinkage was decreased by 87% when EA was exchanged, and the shrinkage was decreased by 70% when SRA was added.

  • PDF

Estimation of the Autogenous Shrinkage of the High Performance Concrete Containing Expansive Additive and Shrinkage Reducing Agent (팽창재와 수축저감제를 조차 사용한 고성능 콘크리트의 자기수축 해석)

  • Han, Min-Cheol
    • Journal of the Korea Institute of Building Construction
    • /
    • v.7 no.3
    • /
    • pp.123-130
    • /
    • 2007
  • This study investigated the fundamental properties and shrinkage properties of high performance concrete with water/binder ratio of 0, 30 and with combination of expansive additive and shrinkage reducing agent. According to the results, the fluidity of high performance concrete showed lower the using method in combination with expansive additive and shrinkage reducing agent than the separately using method of that, so the amount of superplasticizer increased when the adding ratio of expansive additive and shrinkage reducing agent increased. However the air content of concrete increased when used in combination with expansive additive and shrinkage reducing agent, so the amount of AE agent decreased. The compressive strength showed the highest at 5% of expansive additive, and decreased with an increase of the amount of shrinkage reducing agent. Furthermore, in order to reduce the shrinkage of high performance concrete, it was found that the using method in combination with expansive additive and shrinkage reducing agent was more effective than separately using method of that. Autogenous shrinkage was predicted using JCI model. Because JCI model is unable to consider the effect of EA and SRA, correction factor should be added to enhance the accuracy.

Autogenous shrinkage of ultra high performance concrete considering early age coefficient of thermal expansion

  • Park, Jung-Jun;Yoo, Doo-Yeol;Kim, Sung-Wook;Yoon, Young-Soo
    • Structural Engineering and Mechanics
    • /
    • v.49 no.6
    • /
    • pp.763-773
    • /
    • 2014
  • The recently developed Ultra High Performance Concrete (UHPC) displays outstanding compressive strength and ductility but is also subjected to very large autogenous shrinkage. In addition, the use of forms and reinforcement to confine this autogenous shrinkage increases the risk of shrinkage cracking. Accordingly, this study adopts a combination of shrinkage reducing admixture and expansive admixture as a solution to reduce the shrinkage of UHPC and estimates its appropriateness by evaluating the compressive and flexural strengths as well as the autogenous shrinkage according to the age. Moreover, the coefficient of thermal expansion known to experience sudden variations at early age is measured in order to evaluate exactly the autogenous shrinkage and the thermal expansion is compensated considering these measurements. The experimental results show that the compressive and flexural strengths decreased slightly at early age when mixing 7.5% of expansive admixture and 1% of shrinkage reducing admixture but that this decrease becomes insignificant after 7 days. The use of expansive admixture tended to premature the setting of UHPC and the start of sudden increase of autogenous shrinkage. Finally, the combined use of shrinkage reducing admixture and expansive admixture appeared to reduce effectively the autogenous shrinkage by about 47% at 15 days.

An Experimental Study on Chemical and Autogenous Shrinkage of Cement-paste and Mortar (시멘트페이스트와 모르타르의 화학 수축과 자기수축 실험연구)

  • 조경래;박신일;최진영;전철송;임병호;김화중
    • Proceedings of the Korea Concrete Institute Conference
    • /
    • /
    • pp.687-692
    • /
    • 2002
  • The chemical shrinkage and the autogenous shrinkage have been determined experimentally for cement pastes incorporating different W/C ratio and different amount of the following addition: silica fume, fly ash and sand. The measurement method of the chemical shrinkage and autogenous shrinkage both were the volumetric technique. The silica fume has a effect of increasing the autogenous shrinkage while have a minor effect on the chemical shrinkage. The addition of fly-ash and sand both decreased the amount of chemical shrinkage and autogenous shrinkage.

  • PDF

Drying Shrinkage Reduction of Redispersible Polymer Powder-Modified Mortars Using Powdered Shrinkage-Reducing Agent (분말수축저감제를 이용한 제유화형 분말수지 혼입 폴리머 시멘트 모르터의 건조수축 저감효과)

  • ;Ohama, Yoshihiko
    • Proceedings of the Korea Concrete Institute Conference
    • /
    • /
    • pp.231-236
    • /
    • 1998
  • In general, the drying shrinkage of polymer-modified mortars using redispersible polymer powders is much higher than that of unmodified mortar. The purpose of this study is to reduce the drying shringkage of polymer-modified mortars using a redispersible poly(ethylene-vinyl acetate) (EVA) powder, which is widely used for the manufacture of prepackaged-type polymer-modified mortar products at present. Polymer-modified mortars using the redispersible EVA powder with powdered shrinkage-reducing agent were prepared with various polymer-cement ratios and shrinkage-reducing agent contents, and tested for drying shrinkage and strength. From the test results, the drying shrinkage of the redispersible EVA powder-modified mortars with a powdered shrinkage agent is remarkably reduced with increasing shrinkage-reducing agent content, and becomes approximately a half of that of the redispersible EVA powder-modified mortars with the same polymer-cement ratios and without the shrinkage-reducing agent at a shrinkage-reducing agent content of 6%.

  • PDF

Effect of Filling Shrinkage on the Mechanicla Properties of Silk Woven Pabrics (위사수축률이 견직물의 물리적 성질에 미치는 영향)

  • 이승구;박영환
    • Textile Science and Engineering
    • /
    • v.35 no.1
    • /
    • pp.24-30
    • /
    • 1998
  • The structural characteristics and mechanical properties such as tensile, bending, compression and surface of the silk fabrics manufactured by the different shrinkage of filling varns were investigated. For this study, the filling yarn was treated with the salt solution to make shrinkage and. the results obtained are as follows; ① In fabric structure, high shrinkage fabrics have more thickened and bulkier feature with the reduced linearity and yarn integrity than low shrinkage fabric. ② As the filling shrinkage of the fabrics increased, tensile strength decreased, while bending rigidity, compressional energy and bending hysteresis increased. ③ Surface characteristics such as friction coefficient and thickness variation of highly shrinkage fabrics became relatively roughened state. ④ Since stiffened and roughened characteristics of highly shrinkage fabrics, drapabilities of them were significantly lowered. Additionally thermal insulation property of high shrinkage fabric was higher than that of low shrinkage fabric due to bulky and thickened feature. From the results, it is considered that the silk fabrics with high filling shrinkage have the good bulkiness and heat keeping properties and thus they have the suitable characteristics for high quality men's and women's formal gaments.

  • PDF

A Study on the Effect of the Shrinkage Strip on Shrinkage and Thermal Change of Concrete in the Underground Parking Structure (공동주택 지하주차장의 건조수축 및 온도영향에 대한 수축대의 효과 연구)

  • 김록배;김욱종;이도범;이운세
    • Proceedings of the Korea Concrete Institute Conference
    • /
    • /
    • pp.827-832
    • /
    • 2001
  • Shrinkage during the curing and drying of concrete is unavoidable and results in many cracks. Shrinkage strips reduce effectively shrinkage stresses and minimize shrinkage cracks by being left open for a certain time during construction to allow a significant part of the shrinkage to occur without inducing stresses. This study verifies the effectiveness of shrinkage strips and provides the guide for construction of such strips.

  • PDF