• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.11a
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• pp.101-102
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• 2021

The compressive strength of concrete is greatly affected by the temperature inside the concrete at the initial age immediately after pouring. The apparent activation energy of cement and the setting time of concrete are major factors influencing the development of compressive strength of concrete. This study measured the apparent activation energy and setting time according to the change in W/B for each mixing rate of Ground Granulated Blast-Furnace Slag (GGBFS). And after calculating the compressive strength prediction model, the accuracy of the prediction model was evaluated by comparing the predicted compressive strength and the compressive strength.

• Computers and Concrete
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• v.26 no.4
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• pp.309-316
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• 2020

The application of multi-variable adaptive regression spline (MARS) in predicting he long-term compressive strength of a concrete with various admixtures has been investigated in this study. The compressive strength of concrete specimens, which were made based on 24 different mix designs using various mineral and chemical admixtures in different curing ages have been obtained. First, The values of fly ash (FA), micro-silica (MS), water-reducing admixture (WRA), coarse and fine aggregates, cement, water, age of samples and compressive strength were defined as inputs to the model, and MARS analysis was used to model the compressive strength of concrete and to evaluate the most important parameters affecting the estimation of compressive strength of the concrete. Next, the proposed equation by the MARS method using particle swarm optimization (PSO) algorithm has been optimized to have more efficient equation from the economical point of view. The proposed model in this study predicted the compressive strength of the concrete with various admixtures with a correlation coefficient of R=0.958 rather than the measured compressive strengths within the laboratory. The final model reduced the production cost and provided compressive strength by reducing the WRA and increasing the FA and curing days, simultaneously. It was also found that due to the use of the liquid membrane-forming compounds (LMFC) for its lower cost than water spraying method (SWM) and also for the longer operating time of the LMFC having positive mechanical effects on the final concrete, the final product had lower cost and better mechanical properties.

• The Journal of the Acoustical Society of Korea
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• v.39 no.3
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• pp.179-190
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• 2020

In this paper, we estimated the Direction of Arrival (DOA) using Conventional BeamForming (CBF), adaptive beamforming and compressive beamforming. Minimum Variance Distortionless Response (MVDR) and Multiple Signal Classification (MUSIC) are used as the adaptive beamforming, and grid-free compressive sensing is applied for the compressive sensing beamforming. Theoretical background and limitations of each technique are introduced, and the performance of each technique is compared through simulation and real experiments. The real experiments are conducted in the presence of reflected signal, transmitting a sound using two speakers and receiving acoustic data through a linear array consisting of eight microphones. Simulation and experimental results show that the adaptive beamforming and the grid-free compressive beamforming have a higher resolution than conventional beamforming when there are uncorrelated signals. On the other hand, the performance of the adaptive beamforming is degraded by the reflected signals whereas the grid-free compressive beamforming still improves the conventional beamforming resolution regardless of reflected signal presence.

• Korean Journal of Materials Research
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• v.22 no.9
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• pp.494-498
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• 2012

Geopolymer cements and geopolymer resins are newly advanced mineral binders that are used in order to reduce the carbon dioxide generation that accompanies cement production. The effect of additives on the compressive strength of geopolymerized class-F fly ash was investigated. Blast furnace slag, calcium hydroxide($Ca(OH)_2$), and silica fume powders were added to fly ash. A geopolymeric reaction was initiated by adding a solution of water glass and sodium hydroxide(NaOH) to the powder mixtures. The compressive strength of pure fly ash cured at room temperature for 28 days was found to be as low as 291 $kgf/cm^{-2}$, which was not a suitable value for use in engineering materials. On the contrary, addition of 20 wt% and 40 wt% of blast furnace slag powders to fly ash increased the compressive strength to 458 $kgf/cm^{-2}$ and 750 $kgf/cm^{-2}$, respectively. 5 wt% addition of $Ca(OH)_2$ increased the compressive strength up to 640 $kgf/cm^{-2}$; further addition of $Ca(OH)_2$ further increased the compressive strength. When 2 wt% of silica fume was added, the compressive strength increased to 577 $kgf/cm^{-2}$; the maximum strength was obtained at 6 wt% addition of silica fume. It was confirmed that the addition of CaO and $SiO_2$ to the fly ash powders was effective at increasing the compressive strength of geopolymerized fly ash.

• Magazine of the Korean Society of Agricultural Engineers
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• v.17 no.2
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• pp.3749-3757
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• 1975

This study was conducted to investigate some effects of Cemesol on acidresistance and compressive strength of concrete. In mix design of concrete, the cemesol was used as an admixture of cement, and it was added to the mix in an amount equal to 0.1%, 0.2%, 0.3%, and 0.4% by weight of cement of the mix. Concrete specimens were made in accordance with the. Korean Standard Specification for concrete and they were tested for acid-resistance and compressive strength at 2 weeks intervals through 8 weeks. The tests were performed in two cases non-curing and curing for 28 days. The results obtained from the tests are summarized as follows. 1. Refering to acid-resistance test, the cemesol was comparatively effective at every cemesol content except 0.3% in case of non-curing and it was found that cemesol content of 0.4% was the optimum. On the other hand, the cemesol was ineffective in case of curing, but it was seen that cemesol content of 0.1% had some effect at 6 to 8 weeks curing only. 2. Refering to compressive strength test, the cemesol was remarkably effective at a content of 0.1% but it was also shown most inefiective at content of 0.3% in case of non-curing. On the other hand the cemesol was comparatively effective at every content of cemesol except a content of 0.2% in case of curing and it was determined that the cemesol content of 0.3% may be an optimum content. 3. Since optimum cemesol content varied according to acid-resistance, compressive strength and cases such as non-curing and curing, as indicated above may be desirable to choose an optimum cemesol content suitable for purposes and ciroumstances of construction works or conditions of location. 4. The corrosive rate was proportional to compressive strength in case of non-curing, but the relation was reversed in case of curing. It was found that corrosive rate for 8 weeks did not influence compressive strength in case of non-curing but compressive strength in case of curing begins to vary under the influence of corrosion. Thus, corrosion may be more serious to compressive strength in case of curing than that in case of non-curing.

• Magazine of the Korean Society of Agricultural Engineers
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• v.20 no.1
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• pp.4599-4613
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• 1978

This study was intended to investigate the effects of bituminous material content of soil-cement mixtures on their durability. For the purpose, unconfined compressive strength test, Freeze-thaw test, and wet-dry test were performed with three types of soil. Each type of soil was mixed with three levels of cement content and each soil-cement mixture was mixed with four levels of bituminous material content. For the unconfined compressive strength test, Freeze-thaw test and wet-dry test, 324, 108, and 108-specimens were prepared respectively. Unconfined compressive strength was measured at age of 7-days, 14-days and 28-days using 108-specimens in each age. The soil-cement loss rate due to freeze-thaw and wet-dry were calculated after 12 cycles of test using 108-specimens in each test. The results are summarized as follows : 1. Optimum moisture content was increased with increase of cement content, but maximum dry density was changed irregulary with increase of the cement content. 2. The unconfined compressive strength was increased with increase of cement content, bituminous material content and curing age. Cement is more effective factor than bituminous material on unconfined compressive strength of soil-cement Mixture. 3. It is estimated as the most economical cement content that the recommended cement content of A.S.T.M. because increasing rate of unconfined compressive strength at age of 28-days was low when cement content is above the recommanded cement content of A.S.T.M. among all types of soil. 4. Although a portion of cement content is substituted for bituminous material, the necessary unconfined compressive strength can be obtained. 5. The soil-cement loss was more influenced by wet-dry than Freeze-thaw 6. The bituminous material is more effective on the decrease of soil-cement loss than increase of unconfined compressive strength 7. The void ratio of soil-cement mixture was changet irregularly with increase of cement content, but that was decreased in proportion to the increase of bituminous material content. 8. The regression equation between the unconfined compressive strength and soil-cement loss rate were obtained as table 7.

• Journal of the Korea Concrete Institute
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• v.23 no.1
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• pp.67-75
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• 2011

The effect of steel-fiber contents on the compressive behavior of ultra high performance cementitious composites (UHPCC) was studied to propose a compressive behavior model for UHPCC. The experiments considered fiber contents of 0~5 vol.% and the results indicated that compressive strength and corresponding strain as well as elastic modulus were improved as the fiber contents increased. Compared to the previous study results obtained from concrete with compressive strength of 100MPa or less, the reinforcement effect on strength showed similar tendency, while the effect on the strain and elastic modulus were much less. Strength, strain, and elastic modulus according to the fiber contents were presented as a linear function of fiber reinforcement index (RI). Fiber reinforcement in UHPCC had no influence on the shape of compressive behavioral curve. Considering its effect on compressive strength, strain, and elastic modulus, a compressive stress-strain relation for UHPCC was proposed.

• 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.

• The Journal of the Acoustical Society of Korea
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• v.38 no.5
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• pp.534-542
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• 2019

In active SONAR, several different methods are used to detect range-Doppler information of the target. Compressive sensing based method is more accurate than conventional methods and shows superior performance. There are several compressive sensing algorithms for range-Doppler estimation of active sonar. The ability of each algorithm depends on algorithm type, mutual coherence of sensing matrix, and signal to noise ratio. In this paper, we compared and analyzed computational performance and accuracy of various compressive sensing algorithms for range-Doppler estimation of active sonar. The performance of OMP (Orthogonal Matching Pursuit), CoSaMP (Compressive Sampling Matching Pursuit), BPDN (CVX) (Basis Pursuit Denoising), LARS (Least Angle Regression) algorithms is respectively estimated for varying SNR (Signal to Noise Ratio), and mutual coherence. The optimal compressive sensing algorithm is presented according to the situation.

• Structural Engineering and Mechanics
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• v.70 no.4
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• pp.499-511
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• 2019

In this study, the axial compressive behavior of novel quadruple C-channel built-up cold-formed steel columns with different slenderness ratio was investigated, using the experimental and numerical analysis. The axial compressive capacity and failure modes of the columns were obtained and analyzed. The finite element models considering the geometry, material and contact nonlinearity were developed to simulate and analyze the structural behavior of the columns further. There was a great correlation between the numerical analyses and test results, which indicated that the finite element model was reasonable and accurate. Then influence of, slenderness ratio, flange width-to-thickness ratio and screw spacing on the mechanical behavior of the columns were studied, respectively. The tests and numerical results show that due to small slenderness ratio, the failure modes of the specimens are generally local buckling and distortional buckling. The axial compressive strength and stiffness of the quadruple C-channel built-up cold-formed steel columns decrease with the increase of maximum slenderness ratio. When the screw spacing is ranging from 150mm to 450mm, the axial compressive strength and stiffness of the quadruple C-channel built-up cold-formed steel columns change little. The axial compressive capacity of quadruple C-channel built-up cold-formed steel columns increases with the decrease of flange width-thickness ratio. A modified effective length factor is proposed to quantify the axial compressive capacity of the quadruple C-channel built-up cold-formed steel columns with U-shaped track in the ends.