• Geotechnical Engineering
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• v.12 no.3
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• pp.109-126
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• 1996

In this study, the chemical fluid considered is sodium chloride sloutions. The concentrations for the sodium chloride solutions are varied from 0 to 20%. A series of lab oratory triaxial tests are performed on the cylindrical specimens of sand bentonite mixture with different (5, 10, 15%) sodium chloride content solutions. Deformation(elastic modulus, E) and strength (cohesion, c', and angle of friction, f') parameters are obtained from the triaxial tests and they are expressed as functions of conf'ming pressure and sodium chloride solution concentrations. The stress-strain-strength behavior based on the above strength parameters is introduced to the finite element method with a residual flow procedure (RFP). By integrating a slope stability (limit equilibrium) procedure in the finite element method, factors of safety with time are computed.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.10a
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• pp.422-426
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• 2007

CP(Counterpropagation) 알고리즘은 Kohonen의 경쟁 네트워크와 Grossberg의 아웃스타(outstar) 구조의 결합으로 이루어진 것으로 패턴 매칭, 패턴 분류, 통계적인 분석 및 데이터 압축 등 활용분야가 다양하고, 다른 신경망 모델에 비해 학습이 매우 빠르다는 장점이 있다. 하지만 CP 알고리즘은 충분한 경쟁층의 수가 설정되지 않아 경쟁층에서 학습이 불안정하고, 여권 코드와 같이 다양한 패턴으로 그성된 경우에는 패턴들을 정확히 분류할 수 없는 단점이 있다. 그리고 CP 알고리즘은 출력층에서 연결강도를 조정할 때, 학습률에 따라 학습 및 인식 성능이 좌우된다. 따라서 본 논문에서는 패턴 인식 성능을 개선하기 위해 다수의 경쟁층을 설정하고, 입력 벡터와 숭자 뉴런의 대표 벡터간의 차이와 숭자 뉴런의 빈도수를 학습률 조정에 반영하여 학습률을 동적으로 조정하여 경쟁층에서 안정적으로 학습되도록 하고, 출력층의 연결강도 조정시 이전 연결 강도 변화량을 반영하는 모멘텀(momentum)학습법을 적용한 개선된 CP 알고리즘을 제안한다. 학습 성능을 확인하기 위해서 실제 여권에서 추출된 개별 코드를 대상으로 실험한 결과, 본 논문에서 개선한 CP 알고리즘이 기존의 CP 알고리즘보다 패턴 분류의 정확성과 인식 성능이 개선된 것을 확인하였다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.2
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• pp.50-59
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• 2020

Superabsorbent Polymer (SAP) expands inside concrete by absorbing water and contracts as it discharges water. Through this process, concrete can achieve the internal curing effect, but the space occupied by the expanded SAP remains as a void. In this study, the effects of SAP internal curing and voids were evaluated by evaluating the fundamental properties and chloride penetration resistance of SAP mixed concrete. Also, to evaluate the internal curing effect by SAP, the tests were carried out under water and sealed curing conditions, respectively. From the result, the compressive strength of water curing did not differ significantly according to the mixing ratio of SAP. In the case of sealed curing, however, the compressive strength tended to increase as the mixing ratio of SAP increased. The internal curing effect of sealed curing was considered to have influenced the increase in compressive strength. In the case of the chloride diffusion coefficient, the diffusion coefficient tended to decrease as the mixing ratio of SAP increased. In particular, as the sealed curing is applied, the chloride penetration resistance is further improved due to internal curing effect. If the curing conditions are different, it is considered inappropriate to estimate the chloride penetration resistance by the surface electrical resistivity.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.5
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• pp.48-59
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• 2021

In this study, experiments were conducted to investigate the compressive·flexural performances of single fiber-reinforced mortar (FRM) using only steel fiber or carbon fiber which has different material properties as well as hybrid FRM using a mixture of steel and carbon fibers. The mortar specimens incorporated steel and carbon fibers in the mix proportions of 1+0%, 0.75+0.25%, 0.5+0.5%, 0.25+0.75% and 0+1% by volume at a total volume fraction of 1.0%. Their mechanical performance was compared and examined with a plain mortar without fiber at 28 days of age. The experiments of mortar showed that the hybrid FRM using a mixture of 0.75% steel fibers + 0.25% carbon fibers had the highest compressive and flexural strength, confirming by thus the synergistic reinforcing effect of the hybrid FRM. On the contrast, in the case of hybrid FRM using a mixture of 0.5% steel fibers + 0.5% carbon fibers witnessed the highest flexural toughness, suggesting as a result the optimal fiber mixing ratio of hybrid FRM to improve the strength and flexural toughness at the same time. Moreover, the fracture surface was observed through a scanning electron microscope (SEM) for image analysis of the FRM specimen. These results were of great help for images analysis of hybrid reinforcing fibers in cement matrix.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.42 no.2
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• pp.163-170
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• 2022

The present study investigates NO_x-removal and sound-absorption performances of photocatalytic porous concrete prepared by various TiO₂ application methods. Photocatalytic porous concrete samples were prepared by one of the following: 1) mechanically mixing TiO₂ during casting; 2) mixing bottom ash aggregate pretreated with TiO₂ during casting; and 3) spraying TiO₂ solution to the normally fabricated porous concrete. The test results indicated that the mechanical mixing of TiO₂ decreased the compressive strength as the added TiO₂ content increased. The use of pretreated bottom ash aggregate reduced the porosity, yet the compressive strength of the concrete was similar to that measured from the former method. Porous concrete samples sprayed with the TiO₂ solution exhibited enhanced compressive strength, while the porosity was analogous to those measured from other methods. The NO_x-removal performance was the highest in the samples sprayed with the TiO₂ solution, followed by the samples using pretreated bottom ash aggregate and mechanically mixed TiO₂. The samples with mechanically mixed TiO₂ identified a relationship between soundabsorption performance and porosity. However, no particular tendency was observable in the samples with other TiO₂ application methods.

• Geotechnical Engineering
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• v.14 no.1
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• pp.59-70
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• 1998

Samples of silty sands and hydraulic fill ground were investigated by dynamic triaxial teats in order to evaluate the liquefaction strengths. In the tests, (1) undisturbed and disturbed samples were prepared, (2) dynamic shear strengths were measured under isotropic and anisotropic condition, and (3) the test results were compared with the other results which were tested by domestic and foreign researchers. The liquefaction shear strengths under ismtropic test condition were presented in terms of the relative densities. The amount of silt under 30o hardly influenced on the liquefaction strength. In the test results of anisotropically consolidated samples the liquefaction strength was dependent on the magnitude of the effective consolidation ratio. These teat results show that the liquefaction strength of the silty sand in Korea went coast exists within the boundary of the values suggested by Seed and Peacock(1971).

• Journal of Conservation Science
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• v.25 no.2
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• pp.147-154
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• 2009

The change of strength and water vapour diffusion resistant by soluble salts was investigated in the tuff and granite used in many stone monuments of Gyeongju area. With $Na_2SO_4$ and $CaSO_4{\cdot}2H_2O$ were treated the rock samples to understand the difference of solubility. The densities of the tested rocks were increased by the impregnation of $CaSO_4{\cdot}2H_2O$ and $Na_2SO_4$. The flexural strength was increased in the tuff samples but decreased in the granite as the salts increased in the pore. In the tuff, the uniaxial compressive strength was increased by $CaSO_4{\cdot}2H_2O$, but decreased by $Na_2SO_4$. In the granite, it was decreased slightly by $CaSO_4{\cdot}2H_2O$, but increased by $Na_2SO_4$. The water vapour diffusion resistant was increased by the salts in both rocks. As results, it was cleared that the mechanical strength colud be increased in early stage of weathering by the accumulation of salt and water vapour diffusion resistant.

• Journal of the Korean Geosynthetics Society
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• v.16 no.4
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• pp.93-101
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• 2017

In this study, a subjective weighting factors were awarded based on some indication of the difficulty of assessing the preconsolidation stress using traditional methods (Casagrande, Onitsuka et al., Silva, Becker et al., Janbu and Karlsrud methods) such as those proposed by Casagrande and Janbu using undisturbed sample obtained from Gwangyang dredged clay with high plasticity located in the southern area of Korean peninsular. These numbers only assess the relative ease of finding preconsolidation stress and say nothing regarding the accuracy of the value. The data were compared with measurements of undrained shear strength using strength incremental ratio, checking where or not the values are in the range of 0.25 to 0.35 (typical values of Korean marine clay) and analyzing standard deviation(degree of variability). The measurements of undrained shear strength were obtained from unconfined compression tests (UCT). When determining preconsolidation stress of Korean marine clay, at first, the work method proposed by Becker et al. and the bilogarithmic method proposed by Onitsuka et al. should be used. In addition, preconsolidation pressure should be estimated using the traditional Casagrande method as a basic of comparison.

• Journal of the Korean Geosynthetics Society
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• v.15 no.4
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• pp.63-69
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• 2016

In this paper, shear strength characteristics of an unsaturated soil were compared using triaxial compression tests(CD) and modified direct shear tests and thus feasibility of the newly modified direct shear testing apparatus was confirmed. The shear strength tests of unsaturated state with a soil sample, obtained from a slope where debris flow occurred at Yangpyeong in Kyeunggi province during 2010, were performed. Both tests showed a linear relationship of matric suction with the shear strength under low level of matric suction. The apparent cohesion of the unsaturated soil was also increased linearly with increase of matric suction. As results of comparing two different testing apparatus, estimated values of shear strength parameters of unsaturated soil($c^{\prime}$, ${\phi}^b$) were slightly larger in the modified direct shear tests due to constraint effect of shear box.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.5A
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• pp.307-315
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• 2012

Recently, ultra high performance fiber reinforced concrete (UHPFRC) having over 180 MPa compressive strength and 10 MPa tensile strength has been developed in Korea. However, UHPFRC represents different material properties with normal concrete (NC) and conventional high performance concrete (HPC) such as a high early age autogenous shrinkage and a rapid dry on the surface, because it has a low water-binder ratio and high fineness admixtures without coarse aggregate. In this study, therefore, to propose suitable experimental methods and regulations, and to evaluate mechanical properties at a very early age for UHPFRC, setting, shrinkage and tensile tests were performed. From the setting test results, paraffin oil was an appropriate material to prevent drying effect on the surface, because if paraffin oil is applied on the surface, it can efficiently prevent the drying effect and does not disturb or catalyze the hydration of cement. From the ring-test results, it was defined that the shrinkage stress is generated at the time when the graph tendency of temperature and strain of inner steel ring is changed. By comparing with setting test result, the shrinkage stress was firstly occurred as the penetration resistance of 1.5 MPa was obtained, and it was about 0.6 and 2.1 hour faster than those of initial and final sets. So, the starting time of autogenous shrinkage measurement (time-zero) of UHPFRC was determined when the penetration resistance of 1.5 MPa was obtained. Finally, the tensile strength and elastic modulus of UHPFRC were measured from near initial setting time by using a very early age tensile test apparatus, and the prediction models for tensile strength and elastic modulus were proposed.