• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.1A
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• pp.19-24
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• 2011

Concrete columns strengthening effect due to FRP (Fiber Reinforced Polymer) confinement depends on the elastic modulus of the FRP. This study analyzes the retrofitting effect of FRP confinements according to elastic modulus of FRPs using the existing data and suggests a practical model to assess the strengthening effect. This study subdivides the FRP elastic modulus into three parts based on normal concrete and steel elastic modulus. The slope and the y-axis intersection seem to increase with increasing FRP elastic modulus. In addition, the strengthening effect does not develop up to some amount of FRP confinement having relatively smaller elastic modulus than the compressive elastic modulus of concrete. In this case, a linear model to assess the strengthening effect is hard to be used. Thus, this study suggests that the FRP jackets having 2 times larger elastic modulus than that of concrete are recommended to be used for retrofit of concrete and that a linear model can be applied for the case. The suggested model shows nearly the same result regardless to the restraint of the y-axis intersection. This has been observed at the model of steel confinement and, thus, is a reliable result.

• Journal of the Korea Concrete Institute
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• v.28 no.2
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• pp.213-221
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• 2016

Uniaxial compression tests for ultra-high performance hybrid steel fiber reinforced concrete (UHPC) were performed to evaluate the compressive behavior of UHPC. The UHPC for testing contains hybrid steel fibers with a predetermined ratio using a length of 19 mm and 16 mm straight typed steel fibers. Test parameter was determined as a fiber volume ratio to investigate the effect of fiber volume ratio on the strength and secant modulus of elasticity. Test results showed that the compressive strength and elastic modulus of UHPC increased with increasing the fiber volume ratio. Based on the test results, the compressive strength and modulus of elasticity equations were proposed as function of the compressive strength of unreinforced and fiber reinforced UHPC, respectively. The simplified equations for predicting the mechanical properties of the UHPC were a good agreement with the test data. The proposed equations are expected to be applied to the SFRC and UHPC with steel fibers.

• Journal of the Korea Concrete Institute
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• v.14 no.1
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• pp.67-75
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• 2002

For the design of concrete structures in the serviceability limit state, the uniaxial static modulus of elasticity may be a most important parameter. In particular, this may be so just for a deflection control of the structure. Even in new concrete codes, however, the elastic modulus is normally presented on the form of general empirical relationships with the compressive strength and density of concrete. Normally, there is a large uncertainty associated with the general equations obtained by regression. Thus, in a typical plot of static modulus of elasticity vs. compressive strength, a large scatter can be observed at same strength. The aim of this study is to present the method for obtain the maximum modulus of elasticity at same compressive strength. In the present paper report the effects of mix ingredients on the modulus of elasticity of high-strength concrete. The test of 284 cylinder specimens arc conducted for type I with 11 ％ replacement of fly-ash cement concretes. Different water-hinder ratio, amounts of water and coarse aggregate as variables were investigated. And also analyzed it statistically by using SAS.

• Composites Research
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• v.23 no.1
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• pp.17-22
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• 2010

The compressive and dynamic properties of magnetorheological elastomers were investigated as functions of magnetizable particle volume fraction, alignment of the embedded particle and magnetic force. The specimens consisted of pure and filled silicons with randomly dispersed, longitudinal and transverse aligned magnetizable particle chains. To align the embedded particles in the elastomer, the cross-linking of the elastomer composites took place in a magnetic field. The compression and dynamic tests in the absence and the presence of different magnetic forces were carried out. The modulus and loss factor of the elastomer composites increase with increasing volume fraction at the same magnetic force. The case of longitudinal alignment shows a high modulus and loss factor when compared to the case of transverse alignment or random dispersion.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.1A
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• pp.213-218
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• 2006

As a manufacturing process of recycled aggregate improves the quality of recycled aggregate shall be sufficient enough to be used for structural concrete. This study characterized compressive strength and elastic modulus of concrete that used recycled coarse and fine aggregate. Before the strength tests, the fundamental characteristics of recycled aggregate were preliminarily analyzed and the recycled aggregate satisfied the class 1 requirements in KS F 2573. As the replacement ratio increased, the compressive strength and elastic modulus of recycled aggregate concrete decreased. When the coarse and fine aggregates were completely replaced with the recycled, the compressive strength and elastic modulus were decreased by 13% and 31%, respectively. Based on the test results, this study suggests equations for predicting the compressive strength and elastic modulus of the recycled aggregate concrete with respect to the replacement ratio. The values from the equations were in good agreement with the test data from this study and others.

• Proceedings of the KAIS Fall Conference
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• 2011.05a
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• pp.292-295
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• 2011

본 논문에서는 배수성(저소음)포장을 포함하는 2-Layer 아스팔트 포장의 상부층과 하부층의 역학적인 특성을 평가하는데 목적이 있다. 연구 방법으로는 슈퍼페이브 배합설계로 2-Layer 아스팔트 포장의 상 하부층 시편을 제작하였으며, 시편 상부층의 최대공칭치수는 4.75mm이고 하부층의 최대공칭치수는 13mm이다. 이 시편에 대한 기본 물성 시험 실시 후 마샬 안정도 시험에 대한 안정도와 흐름값을 평가하였다. 그리고 상부층과 하부층의 자유단 공진주 시험을 통해 탄성계수(E)를 측정하였고, 비파괴 시험법인 슈미트해머(Schmidt hammer)를 이용해 반발경도를 측정한 후 강도를 추정하였다. 또한 일축압축시험으로 측정된 압축강도로 탄성계수($E_{50}$)를 계산하였다. 마지막으로 각각의 역학적 시험을 통해 얻어진 결과값으로 강도(qu)와 탄성계수 ($E_{50}$)의 상관관계와 추정식으로 구한 강도와 일축압축강도 시험으로 얻어진 강도와의 상관관계를 분석하였고, 자유단 공진주 시험의 탄성계수(E)값과 일축압축시험의 결과로 얻어진 탄성계수($E_{50}$)의 상관관계를 분석하였다.

• Journal of the Korean Society for Railway
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• v.11 no.1
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• pp.61-68
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• 2008

Resilient modulus has been used for characterizing the stress-strain behavior of subgrade soils subjected to traffic loadings. With the recent release of the M-E Design Guide, highway agencies are further encouraged to implement the resilient modulus test to improve subgrade design. The subgrade design for the trackbed, however, is primarily relying on the static test results such as $K_{30}$ and deformation modulus, Ev. Therefore applicability of the resilient modulus for the design of trackbed needs to be evaluated. In this study, physical property tests, unconfined compressive tests and resilient modulus tests were conducted to assess the resilient and permanent strain behavior of 14 cohesive subgrade soils. A predictive model for estimating the resilient modulus is proposed based on the results of unconfined compressive tests and tangent elastic modulus, unconfined compressive strength, failure strain, secant modulus at peak, and yield strain. The predicted resilient moduli using the predictive models compared satisfactorily with measured ones. Although the permanent strain occurs during the resilient modulus test, the permanent behavior of subgrade soils is currently not taken into consideration.

• International Journal of Highway Engineering
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• v.9 no.4
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• pp.205-213
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• 2007

Strength relationships are presented through experimental data from the concrete strength tests in this study. Various strength tests such as the compressive, flexural, and splitting tensile strength and the modulus of elasticity are included. An experimental work was performed to determine the various strength characteristics for various mix designs. Three different coarse aggregates such as granite, limestone, sandstone were used and included were fine aggregates such as natural sand, washed sand and crushed sand. Also included was cement amount as experimental variable. It was confirmed that each strength value with respect to curing time is to follow a typical strength development curve. With this somewhat reliable test results various strength relationships such as flexural strength-compressive strength, splitting tensile strength-compressive strength, modulus of elasticity-compressive strength, splitting tensile strength-flexural strength were analyzed through statistics. Experimental data were well fitted to the 0.5-power relationship of flexural strength and compressive strength which has been commonly accepted. The splitting tensile strength is expected to be best in the linear relationship from the flexural strength data. Finally splitting tensile strength was found to be proportional to the 0.87 power of the cylindrical compressive strength.

• Journal of the Korean GEO-environmental Society
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• v.15 no.2
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• pp.53-58
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• 2014

The uniaxial compressive strength and Young's modulus of intact rocks are the most important analytical parameters for design of rock mass structures. But the preparation of the samples for uniaxial compressive test is a hard and time consuming task. By using ultrasonic test, engineers can predict the analytical parameters that is the uniaxial compressive strength and Young's modulus. The uniaxial compressive test and ultrasonic test were carried out 115 samples of igneous rocks, 74 samples of metamorphic rocks and 55 samples of sedimentary rocks and, after regression analysis of the test results, best fit equations for predicting the uniaxial compressive strength and Young's modulus are proposed. In order to obtain a better correlations coefficient between uniaxial compressive strength and P-wave velocity, the P-wave velocity were multiplied by density values. The proposed equations for predicting uniaxial compressive strength and Young's modulus using ultrasonic test provide reliable results.

• Journal of the Korean Geotechnical Society
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• v.34 no.10
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• pp.39-49
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• 2018

In this study, aimed at determining the elastic modulus of deep mixed samples, 320 test specimens were developed by mixing 8%, 10%, 12%, and 14% of stabilizer mixture in the granular conditions of clay, sand and gravel. Uniaxial compression tests were carried out using these specimens, and the uniaxial compression strength and strain were analyzed to determine the secant elastic modulus and tangent elastic modulus. Laboratory test results showed that the uniaxial compression strength of all deep mixed samples increased with increasing curing time and stabilizer mixing ratio, and that the secant elastic modulus and the tangen elastic modulus also increased. The increase of the elastic modulus according to the curing period turned out greater in the tangent elastic modulus than in the secant elastic modulus. In order to measure elastic modulus with changes in stabilizer mixing ratio, the correlation coefficient between the elastic modulus for stabilizer mixing ratio of 8% and that of 10%, 12% and 14% was calculated respectively by the specimen condition. The elastic modulus tended to increase as the grain size in a deep mixed specimen increased. The distribution of grain size that had the greatest effect appeared when the composition ratio of sand was high. On the other hand, the increase in the elastic modulus was larger in the sand specimens than in the clay and gravel specimens. Based on these results, it is suggested that a pertinent soil parameter of the deep mixed ground in the field may be obtained by the particle size distribution and the mixing ratio of stabilizer of the deep mixed soil.