• Journal of the Korean Magnetics Society
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• 제4권4호
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• pp.303-306
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• 1994

Fundamental characteristics of giant magnetostrictive alloy $Terfenol-D(Tb_{0.3}Dy_{0.7}Fe_{1.9~1.95})$ are rreasured and discussed on the application for actuators. The magnetostriction is measured by laser displacement rreasuring system and the applied compressive stress is measured by load cell. Magnetostrictions increased as the applied compressive stresses increased. When the stress is 7 MPa, the magnetostriction is 1000 ppm at 1500 Oe. As the stresses iocreased from 0 to 14 MPa, the magnetic fields for saturating the magnetostriction also increased. The temperature increased during the experiment is $0.3^{\circ}C$, so the thermal expansion is negligible in these experirrents. The feedback or temperature control function should be added for the precise position control actuator.

• Proceedings of the Korean Institute of Building Construction Conference
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• 한국건축시공학회 2009년도 추계 학술논문 발표대회
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• pp.73-76
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• 2009

In ultra-high-strength concrete, chemical shrinkage is larger than drying shrinkage due to using a large amount of cement and admixtures, and this is a factor deteriorating the quality of structures. Thus, we need a new technology for minimizing the shrinkage strain of ultra-high-strength concrete. So, this study have prepared super-high-strength concrete with specified mixing design strength of over 100MPa and have evaluated a method of reducing chemical shrinkage by using expander and shrinkage-reducing agent. According to the results of this study, with regard to the change in length by chemical shrinkage, an expansion effect was observed until the age of seven days. The expansion effect was higher than previous research that used only expander or shrinkage reducing agent. In addition, ultra-high-strength concrete showed a shrinkage rate that slowed down with time, and the effect of the addition of expander material on compressive strength was insignificant. That is shown that required more database to be accumulated through experimental research for the shrinkage strain of members.

• Journal of the Korean GEO-environmental Society
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• 제12권11호
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• pp.23-30
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• 2011

In this study, Terzaghi's formula was modified to solve problems considering the dilatancy effect of the soil for estimating the earth pressure acting on tunnel. It is performed for the comparison with Terzaghi's formula and modified Terzaghi's formula, tunnel model test result of Kobe University Rock Mechanics Laboratory. From comparison results of the earth pressure acting on tunnel, the earth pressure calculated by the Terzaghi's formula was estimated largest value. The earth pressure measured through the tunnel model test was least value. The difference between the earth pressure derived from Terzaghi's original formula and that derived from the modified formula was caused by the dilation effect, which was caused by the soil volume change. The difference between the earth pressure derived from the modified formula and the earth pressure measured through the tunnel model test, earth pressure results from the energy making failure surface. The results of FEM analysis were almost consistent with the results of mathematical analysis.

• Journal of the Korea Concrete Institute
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• 제24권3호
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• pp.233-240
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• 2012

Hybrid SHCC is being researched actively for its excellent performance in controlling macro and micro cracks using macro and micro fibers, respectively. However, a significant autogenous shrinkage of SHCC is expected since it possesses high unit cement volume in its mix proportion, resulting in autogenous shrinkage cracks. Therefore, this study was performed to evaluate mechanical property of shrinkage-reducing type hybrid SHCC mixed together with steel fiber and PE fiber with excellent micro/macro crack controlling performance. In order to evaluate mechanical property of shrinkage-reducing type hybrid SHCC, replacement ratios of 0% and 10% of expansive admixture and water to binder ratios of 0.45, 0.3, and 0.2 were considered as variables. Then, shrinkage, compressive, flexural, and direct tensile tests were performed. The test results showed that mix proportion with W/B 0.3 significantly improved mechanical performance by using 10% replacement of expansive admixture.

• Journal of the Korea institute for structural maintenance and inspection
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• 제16권2호
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• pp.95-103
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• 2012

In order to improve the dimensional stability and mechanical performance of cement-based composites, the effect of an expansive admixture based on calcium sulphoaluminate (CSA) on the shrinkage and mechanical properties of strain-hardening cement-based composite (SHCC), which exhibits multiple cracks and pseudo strain-hardening behavior in the direct tension, is investigated. Polyethylene fibers reinforced SHCC mixtures with three levels (30, 70, and 100MPa) of compressive strength were compared through free shrinkage, compressive strength, flexural strength, and direct tensile strength measurements. The SHCC mixtures were cast with and without replacing 10% of Portland cement content with CSA admixture. According to test results, CSA admixture is effective in reducing shrinkage of SHCC material. SHCC mixture with CSA admixture exhibited a little higher strength than companion mixture without CSA admixture.

• Journal of the Korea Concrete Institute
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• 제18권3호
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• pp.331-338
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• 2006

This paper presents the experimental results on volumetric changes in ordinary portland cement concrete made with various water-to-cement ratios(W/C's) ranging from 0.32 to 0.50 and cured in low different conditions. Curing regimes employed in this work were designed to exhibit autogenous and drying shrinkage as well as swelling of concrete. The concrete avoided any moist evaporation(Regime f showed only autogenous shrinkage and the lower the W/C, the feater the autogenous shrinkage. The concrete exposed to air drying conditions at $20{\pm}1^{\circ}C$ and $60{\pm}3%$ RH after 6-day water curing at $20{\pm}1^{\circ}C$(Regime II) swelled and then started to shrink. The maximum swelling value of concrete developed in water curing was between 15 and $40{\pm}10^{-6}$, and the greatest total shrinkage(autogenous+drying shrinkage) was obtained for the mixture made with W/C of 0.32. The concrete let to air drying conditions(Regime III) showed greater total shrinkage compared to the concrete cured in Regime II. The concrete exposed to air drying condition after 6-day sealed curing(Regime IV) exhibited slightly smaller total shrinkage than that of the concrete cured in Regime III. Net drying shrinkage that can be derived from the results of Regime I, III, and IV increased as the W/C increased despite of similar total shrinkage. This result indicated that drying shrinkage governs total shrinkage of high-W/C concretes. In other words, a portion of autogenous shrinkage in total shrinkage increased in low-W/C concretes. Therefore, it should be controlled in terms of cracking potential. Finally, total shrinkage of high-strength and high-performance concrete made with low W/C can be effectively reduced by appropriate early moisture curing.

• Proceedings of the Korean Institute of Building Construction Conference
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• 한국건축시공학회 2017년도 춘계 학술논문 발표대회
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• pp.22-23
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• 2017

The purpose of this study is to ascertain self-healing function on microcracks in bisphenol F-type epoxy-modified mortars using expansive admixtures. The specimens are prepared with various polymer-binder ratios of 0, 5, 10, 20%, expansive admixture contents of 0% and 10%, a sodium carbonate content of 0.25%, and subjected to exposure conditions of CR1, CR2, CR3 and CR4. The specimens are tested for self-healing effect, porosity and FE-SEM analysis. As a result, self-healing effects of bisphenol F-type EPMMs with expansive admixtures are visible in all of the outdoor exposure conditions. In particular, exposure conditions of CR3 and CR4 are most noticeable. And the porosity of EPMMs is reduced with an increase in the polymer-binder ratio, and is considerably smaller than that of unmodified mortar.

• Proceedings of the Korean Institute of Building Construction Conference
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• 한국건축시공학회 2015년도 춘계 학술논문 발표대회
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• pp.166-167
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• 2015

The purpose of this study is to examine the effect on drying shrinkage of self-healing epoxy-modified mortars(EPMMs) using expansive admixtures. The EPMMs are prepared with polymer-binder ratios of 0 and 10%, and tested for drying shrinkage and pore structure analysis. As a result, regardless of the expansion and swelling agent content, the drying shrinkage of the EPMMs is remarkably decreased than that of unmodified mortars. Also, the pore size distribution of the EPMMs is moved to smaller size in comparison with unmodified mortars. In this study, the EPMM with expansive agent 7.5% and swelling agent 2.5% is recommended as a optimal mix proportion for reduction of drying shrinkage.

• Journal of the Korea institute for structural maintenance and inspection
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• 제18권1호
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• pp.101-110
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• 2014

Expansion agent is a very effective admixture for prevention of cracking due to autogenous/drying shrinkage and this can induce internal chemical prestress to embedded reinforcement. In this paper, tension-softening and hardening in cement mortar with steel and CSA expansion agent are experimentally evaluated. Cement mortar with steel reinforcement is prepared and tensile strength test is performed for evaluation of cracking and tensile behavior. In spite of slightly reduced strength and elasticity in CSA mortar, significantly increased tension-hardening behavior is evaluated in CSA mortar with induced chemical prestress. Furthermore previous tension softening models are compared with the test results and improvement are proposed.

• Journal of the Korea institute for structural maintenance and inspection
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• 제18권5호
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• pp.34-40
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• 2014

High-performance fiber-reinforced cement composite (HPFRCC) shows very high autogenous shrinkage, because it contains a low water-to-binder ratio (W/B) of 0.2 and high fineness admixture without coarse aggregate. Thus, it needs a method to decrease the cracking potential. Accordingly, in this study, to effectively reduce the shrinkage of HPFRCC, a total of five different ratios of SRA (1% and 2%), EA (5% and 7.5%), and a combination of SRA and EA (1% and 7.5%) were considered. According to the test results of ring-test, a combination of SRA and EA (1% and 7.5%) showed best performance regarding restrained shrinkage behavior without significant deterioration of compressive and tensile strengths. This was also verified by performing modified drying shrinkage crack test.