• Magazine of the Korean Society of Agricultural Engineers
• /
• v.28 no.2
• /
• pp.74-86
• /
• 1986

유동화콘크리트의 공학적 특성에서 시간-의존거동을 확인하기 위하여,나프타렌 설폰산염 폴리머 고축합물인 Rheobuild 1000과 메라민 설폰산염 고축합물인 NP-20의 고성능감수제를 사용한 유동화콘크리트와 보통콘크리트를 제조하여 비교.고찰을 행하였으며, 고성능감수제의 종류 및 함량이 콘크리트의 공학적 특성에 미치는 영향을 구명하기 위하여 재령 3일, 14일, 28일, 60일, 90일, 180일의 압축강도를 측정, 조기 및 장기압축강도를 조사하였고, 인장강도 및 탄성 변형에 미치는 영향을 조사하였다. 또한 습윤 및 에어콘디션의 양생조건하에서 시간의 경과에 따른 건조수축 및 크리이프 변형을 조사.분석함으로써 유동화콘크리트의 시간-의존거동을 확인하였다. 실험결과, 사용 고성능 감수제의 종류에 따라 차이는 있으나, 고성능 감수제의 사용은 일반적으로 워커빌리티 성능을 개선하고 압축 및 인장도를 크게 향상시키며, 탄성계수는 보통의 콘크리트에 비하여 높게 나타났다. 또한 건조수축 및 크리프 변형의 감소에 매우 양호한 결과를 나타내어 앞으로 건설용 용도로써 효과적인 것으로 판단되었다.

• Journal of the Korea Concrete Institute
• /
• v.25 no.6
• /
• pp.613-620
• /
• 2013

Concrete has been recognized as a material which is resistant to high temperatures, but chemicophysical property of concrete is changed by the high temperature. So, mechanical properties of concrete may be reduced. Because of this, standards and researches on the degradation of the mechanical properties of concrete at high temperatures have been presented. However, research data about the state that considering the loading condition and high-strength concrete is not much. Therefore, this study evaluated the high-temperature properties of high-strength concrete by loading condition and elevated temperature. The stress-strain, strain at peak stress, compressive strength, elastic modulus, thermal strain and the transient creep are evaluated under the non-loading and $0.25f_{cu}$ loading conditions on high strength concrete of W/B 12.5%, 14.5% and 20%. Result of the experiment, decrease in compressive strength due to high temperature becomes larger as the compressive strength increases, and residual rate of elastic modulus and compressive strength is high by the shrinkage caused by loading and thermal expansion due to high temperature are offset from each other, at a temperature above $500^{\circ}C$.

• Journal of the Korea Institute of Building Construction
• /
• v.16 no.4
• /
• pp.305-311
• /
• 2016

This study examined the long-term inelastic characteristics, including unrestrained shrinkage and creep, of low-heat cement concrete under different ambient curing temperatures. To achieve the designed compressive strength of 42MPa, water-to-binder ratios were selected to be 27.5, 30, and 32.5% for curing temperatures of 5, 20, and $40^{\circ}C$, respectively. Test results showed that the shrinkage strains of concrete mixtures tended to decrease with the decrease in curing temperature because of the delayed evaporation of internal capillary and gel waters. Meanwhile, creep strains were higher in concrete specimens under lower curing temperature due to the occurrence of the transition temperature creep. The design models of KCI provision gave better accuracy in comparison with test results than those of ACI 209, although a correction factor for low-heat cement needs to be established in the KCI provision.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.8 no.4
• /
• pp.87-96
• /
• 2004

As a special concrete, which is a mixture of soil, cement and water, has strength like regular concrete for pavement, soil cement has been used in various field such as pavement and soft soil improvement. The objective of this study was to investigate the characteristic of unconfined compressive strength and time dependent behavior of soil cement that is made from decomposed granite soil or coluvial and inorganic solidification liquid. The results showed that the unconfined compressive strength appears to increase as the amount of cement and curing time increase In addition, the strength seems to decrease with increase of the potion of fine particles(No 200 sieve). The result of XRD indicated that there is Vermiculite, the product of reaction, in the soil cement. The dynamic properties of material, such as shear complex compliance, shear complex modulus, and phase angle could be calculated from the hysteresis loop obtained from the Haversine Creep Tests. Finally, creep behavior was able to be predicted from these dynamic properties.

• Journal of the Korea Concrete Institute
• /
• v.23 no.5
• /
• pp.627-636
• /
• 2011

Recently, to prevent explosive spalling of high-strength concrete (HSC) members, the usage of nylon fiber instead of polypropylene fiber has increased. Past experimental studies have been conducted to examine the spalling and mechanical properties of HSC with nylon fibers when exposed to elevated temperature. However, the previous studies on HSC with nylon fibers subjected to high temperatures were performed only on the properties such as spalling, compressive strength, and elastic modulus rather than investigations on to the behaviors such as thermal strain, total strain, steady state creep, and transient creep. Therefore, in this study thermal strain, total strain, steady state creep, and transient creep of HSC mixed with nylon fibers with water to binder ratio of 0.30 to 0.15 were tested. The experimental results showed that nylon fibers did not affect the performance of HSC with nylon fibers at high temperatures. However, HSC with nylon fibers generated a larger transient creep strain than that of HSC without fibers and normal strength concrete.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2009.11a
• /
• pp.81-85
• /
• 2009

In the recent years, the high strength concrete has increasingly been used according to extending market of tall buildings. However, Ministry of Land, transport and Maritime Affairs was established by law with an alternative plan after June 2008 because of the weakness of high strength concrete accompanied spalling phenomena in fire. The mix design of concrete has to properly meet standards which are the spalling resistance of concrete and limited temperature of steel reinforcement. The fire proof concrete mixed fiber has widely been used to meet spalling safety on the many construction sites, the most researches about the fire proof concrete mixed fiber had being carried out focused on fire resistance, compressive strength and cast in place of concrete. But the most important thing is column shortening used the fire proof concrete within the vertical members. In this paper, the fire proof concrete filled spalling safety standards was experimented by required material when the column shortening is revised between normal concrete and fire proof concrete mixed fiber and then the results have done a comparative analysis. Also, The paper aimed to indicate a basic data for revision of column shortening of fire proof concrete.

• Journal of the Korea Concrete Institute
• /
• v.25 no.4
• /
• pp.429-438
• /
• 2013

An object oriented numerical analysis program of axial-flexural elements and the step-by-step method (SSM) has been developed to analyze concrete long-term behaviors of structures constrained internally and externally. The results of the numerical analysis for simple and continuous prestressed (PS) concrete box and composite girders, pre-cast slab of continuous steel composite girder, and simple preflex composite girder show that the adjusting coefficient decreases by increasing constraint. The loss rates of pre-tension force were not sensitive but those of pre-compression force were increased rapidly by decreasing adjusting coefficient. This indicates that the design based on the loss rate of pre-tension can over-estimate the pre-compression force in a concrete section constrained internally and externally. The adjusting coefficients which satisfy results of the numerical analysis are 0.35~0.95, and it can be used as an index of constraint of concrete long-term deformation. The adjusting coefficient 0.5 of Bridge Design Specifications can under-estimate residual stress of PS concrete slab, and the coefficient 0.7 or 0.8 of LRFD Bridge Designing Specifications can under-estimate the loss rates of continuous PS concrete girders. The adjusting coefficient of hybrid structures should be less then 0.4.

• Magazine of the Korea Concrete Institute
• /
• v.8 no.3
• /
• pp.135-146
• /
• 1996

In this study, the properties of super flowing concrete containing fly ash were experimentally investigated and compared with those of ordinary concrete. Tests were carried out on five types of super flowing concrete mixes containing fly ash and three types of ordinary concrete mixes without fly ash. Flow test, 0-funnel test, box test, L type test and slump test were carried out to obtain the properties for flowability and workability of fresh concrete. The mechanical properties of hardened concrete were also investigated in terms of compressive strength, splitting tensile strength, modulus of elasticity, creep and drying shrinkage. In fresh concrete, it was found that super flowing concrete had excellent workability and flowability compared with ordinary concrete, and had self-compactable performance. Super flowing concrete *also had good mechanical properties at both early and late ages with compressive strength reaching as high as 40 MPa at 28 days. The creep deformation of super flowing concrete investigated was relatively lower than that of ordinary concrete, but drying shrinkage was much higher.

• Journal of Korean Society of Steel Construction
• /
• v.24 no.5
• /
• pp.571-582
• /
• 2012

Prestressed composite girders provide efficient composite action by applying prestress to the sub-encasing concrete. In this study, an enhanced prestressed composite girder with forms suspended from the steel girder is utilized. Long-term behavior of the prestressed composite girder is estimated using age-adjusted effective modulus method, which is verified experimentally using measurements obtained from an in-service bridge. Then, parametric study is carried out to investigate the influences caused by ambient temperature, humidity, prestressing and concrete casting date.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.22 no.1
• /
• pp.208-215
• /
• 2018

The causes of column shrinkage and the codes that have been studied up to now are discussed. The documents mentioned in the code deal with the drying shrinkage, creep, compressive strength and elastic modulus of the specimen, and the elastic deformation calculated from the structural analysis. However, the deformation due to the temperature caused by the long term monitoring is less than that caused by the factors generated by the previous studies. In the previous studies, it was found that dehydration shrinkage, creep, and elastic deformation were not considered for temperature-induced deformation, while for the specimen experiments, the temperature-related items were replaced with the humidity-related terms The compensation value by the proposed equation showed error of 4.9 mm in the upper direction and 1.0mm in the lower direction when calculating column shortening, and it was found that its value by the proposed equation almost coincided with the measurement value in Site. Therefore, it is necessary to further study the temperature that can be omitted in calculating the existing column shortening, to consider the influence factors, and to supplement the criteria for the temperature measurement of the structure as well as the specimen tests.