• Tunnel and Underground Space
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• v.31 no.6
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• pp.469-479
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• 2021

As a material for preventing spalling of concrete, the effectiveness of PP fiber has already been confirmed. However, it is necessary to consider the maximum temperature that occurs during a fire, and to solve the mixing problem and the strength reduction problem that occur depending on the mixing amount. In this study, the fire resistance performance of tunnel segment linings according to the PP fiber content and air volume under the RABT fire scenario was investigated. As a result, no spalling or cross-sectional loss occurred in all test specimens, and when the PP fiber content was small, the maximum temperature was relatively high and the maximum temperature arrival time was also fast. On the other hand, no trend was found for the maximum temperature and arrival time according to the difference in air volume. In the internal temperature distribution results for the PP fiber mixing amount of 0.75, 1.0, 1.5, and 2.0 kg/m³, the results of 0.75 and 1.0 kg/m³ showed similar temperature distribution, and the results of 1.5 and 2.0 kg/m³ were similar. It was confirmed that the internal temperature distribution tends to decrease at the same depth when the amount of PP fiber mixed is large, and it was confirmed that a remarkable difference occurred from the results of 1.0 kg/m³ and 1.5 kg/m³ of PP fiber mixed amounts.

• Journal of Aquaculture
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• v.7 no.4
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• pp.239-249
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• 1994

This study was conducted to elucidate mixing characteristics of the media to dertermine hydraulic model parameters of the three phase fluidized bed for the water quality management of aquaculture. The volume and H/D ratio of the reactor were 1.76 Liter and 10.9, respectively. The experimental results showed that variance $(\sigma^2)$ and dispersion number $(D/{\mu}L)$ were above 0.47 and $0.35\~\infty$, respectively. Therefore, the condition of the reactor was almost ideal complete mixing. The dependence of the overall oxygen-transfer coefficient $(K_{La})$ on each experimental variables through a multple linear regression was given by the following equation ; $$K_{La}\;=\;44.9(D_i/D_c)^{-0.4611}\;A_f^{0.8622}\;C_m^{-0.0746}\;d_p^{-0.4302}$$

• Journal of the Korea Institute of Building Construction
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• v.18 no.2
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• pp.133-140
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• 2018

The objective of this study is to propose a reliable mixing design procedure of concrete using artificial lightweight aggregate produced from expanded bottom ash and dredged soil. Based on test results obtained from 25 mixes, empirical equations to determine water-to-cement ratio, unit cement content, and replacement level of lightweight fine aggregates were formulated with regard to the targeted performance (compressive strength, dry density, initial slump, and air content) of lightweight aggregate concrete. From the proposed equations and absolute volume mixing concept, unit weight of each ingredient was calculated. The proposed mix design procedure limits the fine aggregate-to-total aggregate ratio by considering the replacement level of lightweight fine aggregates, different to previous approach for expanded fly ash and clay-based lightweight aggregate concrete. Thus, it is expected that the proposed procedure is effectively applied for determining the first trial mixing proportions for the designed requirements of concrete.

• Journal of the Korean GEO-environmental Society
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• v.1 no.1
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• pp.87-96
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• 2000

Generally, OPC(ordinary portland cement) is used for grouting in Korea, and bentonite has usually been added to prevent the deposition of cement particles. The dispersion of CB(cement bentonite) grout is influenced by variable factors i.e. water to cement ratio, particle size of cement, kind of bentonite, adding volume, method of adding, viscosity of CB grout materials and curdling time. Among variable factors, the viscosity of CB grout materials is influenced by the dispersion, and dispersion is improved as the speed of grout mixer increase. In this paper, the specification of construction was derived by estimating physical characteristics of CB grout materials and confirming the sate of dispersion. The results show that the engineering characteristics of CB grout materials vary with the water to cement ratio and the mixing speed.

• Journal of the Korea Institute of Building Construction
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• v.10 no.4
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• pp.3-9
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• 2010

Fire resistance and material properties of high-strength concrete (W/B 21.5%, 28.5%) with OPC, BS and FA were tested in this study. Main factors of the test consisted of fiber mixing ratio and W/B. Two types of fiber (NY, PP) mixed with the same weight were used for the test. The fiber mixing ratios were 0%, 0.05%, 0.1%, and 0.2% of the concrete weight. After performing the test, Under the W/B level of 21.5% and 28.5%, the spalling was effectively resisted by using the high strength concrete with fiber mixing ratios of 0.05%~0.1%. Compressive strength, flowability and air content are similar those of the fiberless high-strength concrete with the same W/B.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.601-604
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• 2008

This study as using admixture (G), high early strength agent, calcium hydroxide {a(OH)2} and fine particle cement, etc which have been newly developed for the purpose of quality improvements like the improvement of early strength of concrete that the FA was substituted by 20%, etc, reviewed the possibility of the utilization in the great quantity and the results are summarized as the followings. Slump loss by the kind of mixing material of high early strength agent and Ca(OH)$_2$ showed the smaller width of decrease than that of plain to appear the improved results and fine particle cement and G admixture showed the large slump loss. Air contents were appeared to satisfy the target air contents at all mixing materials. Regarding the compressive strength of the concrete by the kind of mixing material, G admixture was appeared to be highest all on aging 3 days, 7days and 28days at the initial strength. And fine particle cement and high early strength agent showed higher strength increase rate on aging 3days than plain but showed that the increase of strength becomes gradually dulled as aging is increased. And Ca(OH)$_2$ had almost no effect.

• Korean journal of food and cookery science
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• v.25 no.3
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• pp.317-329
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• 2009

In the study, we determined the optimal ingredient mixing ratio for the preparation of sponge cake containing bamboo (Pseudosasa japonica Makino) leaves. This experiment was designed in according with the D-optimal design of mixture design, which involved 14 experimental points including 4 replicates for three independent variables (sugar 110${\sim}$129%, bamboo leaves 3${\sim}$8%, oil 10${\sim}$25%). The results the F-test, specific gravity, volume and color values (L, a, b) decided a linear model, while the viscosity, hardness and sensory characteristics (color, smell, taste, texture and overall acceptance) decided a quadratic model. The results of our fitness analysis demonstrated that in all characteristic, the probabilities were significant within 0.05%; thus, the models were accepted as appropriate. The response surface and trace plot results demonstrated that increasing amounts of added bamboo leaves induced a reduction in brightness, and increasing redness and yellowness. In addition, increasing amounts of bamboo leaves caused increases in hardness, and thus the softness of the cake decreased. And as the level of added oil increased, softness increased. Cake samples received low sensory evaluation scores when sugar, bamboo leaves, and oil were added above their optimal levels. In the numeric optimization, the optimal ingredient amounts were 121.36% sugar, 4.96% bamboo leaves, and 15.69% oil. The above results demonstrate the feasibility of adding bamboo leaves to sponge cake, and therefore, a bamboo leaves as a functional food.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1999.10a
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• pp.27-27
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• 1999

To illustrate the global variation of the droplet mean diameters and the turbulent flow characteristics in counterflowing internal mixing pneumatic nozzle, the experimental measurements at five axial downstream locations(i.e., at Z=30, 50, 80, 120, and 170mm) were made using a PDPA(Phase Doppler Particle Analyzer) under the different air injection pressures ranging from 40 ㎪ to 120 ㎪. A nozzle with axi-symmetric tangential-drilled four holes at an angle of 15$^{\circ}$ has been designed and manufactured. The distributions of velocities, turbulence intensities, turbulence kinetic energy, turbulent correlation coefficients, spray angle, droplet mean diameters, volume flux, number density are quantitatively analyzed. It is possible to discern the effects of increasing air pressure. It indicates that the strong axial momentum in spite of more or less disparity between the velocity components means more reluctant to disperse radially, and that axial fluctuating velocities are substantially higher than those of radial and tangential ones, suggesting that the disintegration process is enhanced under higher air assist. The larger droplets are detected in the spray centerline at the near stations and smaller ones are generated due to further subsequent breakup at farther axial locations are attributed to the internal mixing type nozzle characteristics. Despite of the strong axial momentum, the poor atomization around the centre close to the nozzle exit is attributed to the lower rates of spherical particles which are not subject to instantaneous breakup. As it goes downstream, however, substantial increases in SMD(Sauter Mean Diameter) from the central part toward spray periphery are understandable because the droplet relative velocity is too low to bring about any subsequent disintegration.

• KSBB Journal
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• v.7 no.1
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• pp.59-65
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• 1992

Hydrodynamics and mixing characteristics such as circulation time, mixing time, circulation velocity and axial dispersion coefficient were investigated using highly viscous pseudoplastic solutions of carboxymethyl cellulose(CMC) in an external circulation loop air-lift reactor with 13$\ell$ working volume. The superficial gas velocity was changed from 1.9 to 6.2cm/s and CMC concentration from 0 to 1.0wt%. The theoretical model based on the pressure balance is developed mathematically to predict liquid circulation velocity. Gas hold-up, circulation velocity and axial dispersion coefficient of liquid phase increased with increasing gas velocity and decreased slightly with increasing liquid viscosity. Mixing time and circulation time decreased with increasing gas velocity and increased with increasing liquid viscosity. Experimental data on liquid circulation velocity were in good agreement with the predicted values.

• Journal of Digital Convergence
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• v.18 no.4
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• pp.341-346
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• 2020

Polymethyl methacrylate (PMMA), a self-curing resin mainly used in removable orthodontic appliances, is an acrylic resin mainly used in the field of modern dentistry. As an advantage, it has been used for a long time as a material for orthodontic devices in dentistry due to its color and volume, tissue affinity, and stability. The production of PMMA can be divided into self-polymerization method and thermal polymerization method according to activation method. Self-curing resins have long been used as orthodontic devices. The resin injection method is largely divided into a sprinkle-on method and a mixing method. In this study, we intend to test the mechanical properties according to the resin injection method of the orthodontic device, such as strength, modulus of elasticity, and surface roughness. There was no significant difference in strength as a result of three-point bending strength test on rectangular specimens (1.4 × 3.0 × 19.0 mm) of orthodontic PMMA. There was also no significant difference in hardness. There was no significant difference in surface roughness. It was confirmed that the orthodontic PMMA had no significant difference in mechanical properties according to the resin injection method of the orthodontic device.