• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.6A
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• pp.573-580
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• 2010

This paper presents the development of self-consolidating concrete (SCC) using lightweight aggregates. SCC using Lightweight aggregate properties have been evaluated in terms of flowability, segregation resistance and filling capacity of fresh concrete as per the standards of the Japanese Society of Civil Engineering (JSCE). The measurement of the mechanical properties of hardened SCC using lightweight aggregate, including compressive strength, splitting tensile strength, elastic moduli and density, as well as its dry shrinkage and carbonation properties were also carried out. The characteristics of SCC using lightweight aggregate at the fresh state showed that as the use of the lightweight aggregate, the flowability improves without exception of Mix No. 9 but the segregation resistance tends to decrease without exception of Mix No. 3, 4 and 5. The 28 days compressive strength of the SCC using lightweight aggregate was found to be 30 MPa or higher. The relationship between the compressive strength and the splitting tensile strength was found to be similar to the expression presented by CEB-FIP, and the relationship between the compressive strength and the elastic moduli was found to be similar to the expression suggested by ACI 318-08 which takes into consideration the density of concrete. The density of the SCC using lightweight aggregate decreased by up to 26% compared to that of the control SCC. Also, The dry shrinkage and carbonation depth of the SCC using lightweight aggregate increased compared to that of the control SCC.

• The Journal of Engineering Geology
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• v.33 no.4
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• pp.599-609
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• 2023

In the seismic retrofitting of harbor breakwaters in Korea, the recovery rate is often uncertain due to site conditions and site conditions, and problems continue to arise. Therefore, in this study, we analyzed the recovery rate and compressive strength of the improved material through drilling survey by grouting confirmation method after applying low-fluidity mortar injection method, and furthermore, we checked the elastic modulus by downhole test and tomography to confirm the reinforcement effect of soft ground after ground improvement. The experimental results showed that the average shear wave velocity of the ground increased from 229 m/s to 288 m/s in BH-1 and BH-3 boreholes to a depth of 28.0 m, and the average shear wave velocity of the ground to a depth of 30.0 m tended to increase from 224 m/s to 282 m/s in the downhole test. This is believed to be a result of the increased stiffness of the ground after reinforcement. The results of the tomographic survey showed that the Vs of the soft ground of the sample at Site 1 increased from 113 m/s to 214 m/s, and the Vs of the sample at Site 2 increased from 120 m/s to 224 m/s. This shows that the stiffness of the ground after seismic reinforcement is reinforced with hard soil, as the Vs value satisfies 180 m/s to 360 m/s in the classification of rock quality according to shear wave velocity.

• Journal of the Korean Institute of Gas
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• v.27 no.4
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• pp.19-26
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• 2023

Earthquakes are one of the most important disasters affecting underground structures. Urban gas underground pipes may cause safety problems of structures in the event of an earthquake. Since Korea began digital observation, the number of earthquakes has been steadily increasing. The seismic design standard for urban gas pipes was established in 2008, but it is difficult to estimate the impact of pipes in the event of an earthquake based on the installation of pipes. In this study, structural analysis was performed on PE (polyethylene pipe) pipes and PLP (polyethylene coated steel pipe) pipes, which are mainly used as buried pipes in Korea, according to environmental and pipe variables in the event of an earthquake. This study sought to find the variables of the most vulnerable buried pipe by modeling pipes through Computer Aided Engineering (CAE) and generating displacement on the ground. Through this study, it was confirmed that the larger the elastic modulus of the soil, the deeper the buried depth, the smaller the tube diameter, and the higher the pressure, the more PLP pipes are affected by earthquakes than PE. Based on these results, the vulnerable points of buried urban gas pipes are inferred and used for special inspections of buried pipes in the event of an earthquake.

• Food Science and Preservation
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• v.31 no.1
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• pp.126-137
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• 2024

In this study, zinc oxide nanoparticles (ZnONPs) were synthesized using three distinct zinc salts: zinc acetate, zinc chloride, and zinc nitrate. These ZnONPs were subsequently utilized in the fabrication of carrageenan-ZnONPs (Car-ZnONPs) composite films. The study assessed influence of the various ZnONPs on the morphological, water vapor barrier, color, optical, and antimicrobial properties of the Car-ZnONPs composite films. The surface morphology and UV-blocking attributes of the composite films were affected by the type of ZnONPs used, but their surface color, transparency, and chemical structure remained unaltered. The composite film's thickness and elongation at break (EB) significantly increased, while the tensile strength significantly decreased. In contrast, film's elastic modulus (EM) and water vapor permeability coefficient (WVP) showed no significant difference. All the composite films with added ZnONPs demonstrated potent antibacterial activity against Escherichia coli O157:H7 and Listeria monocytogenes . Among the carrageenan-based composite films, Car-ZnONPs^ZC showed the highest antibacterial and UV-blocking properties, and its elongation at break was significantly higher than that of the pure carrageenan films. This suggests that ZnONPs composite films have the potential to be used as an active packaging film, preserve the safety of the packaged food and extend shelf life.

• Journal of Korean Tunnelling and Underground Space Association
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• v.26 no.4
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• pp.327-344
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• 2024

In general tunnel design and analysis, rock masses are often assumed to be isotropic. Under isotropic conditions, material properties are uniform in all directions, leading to a higher evaluation of tunnel stability. However, actual rock masses exhibit anisotropic characteristics due to discontinuities such as joints, bedding planes, and faults, which cause material properties to vary with direction. This anisotropy significantly affects the stress distribution during tunnel excavation, leading to non-uniform deformation and increased risk of damage. Therefore, thorough pre-analysis is essential. This study analyzes the displacement and stress changes occurring during tunnel excavation based on rock anisotropy. A three-dimensional numerical analysis was performed, selecting anisotropy index and dip angles as variables. The results showed that as the anisotropy index increased, the displacement in the tunnel increased, and stress concentration became more pronounced. The maximum displacement and shear stress were observed where the dip planes met the tunnel.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.2
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• pp.133-144
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• 2006

In order to catch out such Bond Strength, the preceding researchers had ever examined the Bond Strength of FRP Plate through their experimentations by setting up of various fluent. However, since the experiment for research on such Bond Strength takes much of expenditure for equipment structure and time-consuming, also difficult to carry out, it is conducting limitedly. This Study purposes to develop the most suitable Artificial Neural Network Model by application of various Neural Network Model and Algorithm to the adhering experiment data of the preceding researchers. Output Layer of Artificial Neural Network Model, and Input Layer of Bond Strength were performed the learning by selection as the variable of the thickness, width, adhered length, the modulus of elasticity, tensile strength, and the compressive strength of concrete, tensile strength, width, respectively. The developed Artificial Neural Network Model has applied Back-Propagation, and its error was learnt to be converged within the range of 0.001. Besides, the process for generalization has dissolved the problem of Over-Fitting in the way of more generalized method by introduction of Bayesian Technique. The verification on the developed Model was executed by comparison with the resulted value of Bond Strength made by the other preceding researchers which was never been utilized to the learning as yet.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2000.09a
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• pp.201-210
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• 2000

Rock bridge in rock masses can be considered as one of several types of opening-mode fractures, and also it has been known to have a great influence on the stability of structures in rock mats. In the beginning of researching a rock bridge it used to be studied only in characteristics of its behavior, as considering resistance of material itself. However the distribution pattern of rock bridges, which can affect the stability of rock structures, is currently researched with a fracture mechanical approach in numerical studies. For investigating the effect of rock bridges on the development pattern of hydraulic fractures, the author analyzed numerically the stress state transition in rock bridges and their phenomena with a different pattern of the rock bridge distributons. From the numerical studies, a two-crack configuration could be defined to be representative of the most critical conditions for rock bridges, only when cracks are systematic and same in their length and angle. Moreover, coalescence stresses and onset of propagation stresses could be known to increase with decreasing s/L ratio or increasing d/L ratio. The effect of pre-existing crack on hydraulic fracturing was studied also in numerical models. Different to the simple hydraulic fracturing modeling in which the fractures propagated exactly parallel to the maximum remote stress, the hydraulic fractures with pre-existing cracks dial not propagate parallel to the maximum remote stress direction. These are representative of the tendency to change the hydraulic fractures direction because of the existence of pre-existing crack. Therefore s/L, d/L ratios will be identical as a function effective on hydraulic fractures propagation, that is, the $K_{I}$ vague increase with decreasing s/L ratio or increasing d/L ratio and its magnification from onset to propagation increases with decreasing s/L ratio. The scanline is a commonly used method to estimate the fracture distribution on outcrops. The data obtained from the scanline method can be applied to the evaluation of stress field in rock mass.s.

• Tunnel and Underground Space
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• v.10 no.3
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• pp.447-456
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• 2000

Rock bridge in rock masses can be considered as one of several types of opening-mode fractures, and also it has been known to have a great influence on the stability of structures in rock mass. In the beginning of researching a rock bridge it used to be studied only in characteristics of its behavior, as considering resistance of material itself. However the distribution pattern of rock bridges, which can affect the stability of rock structures, is currently researched with a fracture mechanical approach in numerical studies. For investigating the effect of rock bridges on the development pattern of hydraulic fractures, the author analyzed numerically the stress state transition in rock bridges and their phenomena with a different pattern of the rock bridge distributions. From the numerical studies, a two-crack configuration could be defined to be representative of the most critical conditions for rock bridges, only when cracks are systematic and same in their length and angle. Moreover, coalescence stresses and onset of propagation stresses could be known to increase with decreasing s/L ratio or increasing d/L ratio. The effect of pre-existing crack on hydraulic fracturing was studied also in numerical models. Different to the simple hydraulic fracturing modeling in which the fractures propagated exactly parallel to the maximum remote stress, the hydraulic fractures with pre-existing cracks did not propagate parallel to the maximum remote stress direction. These are representative of the tendency to change the hydraulic fractures direction because of the existence of pre-existing crack. Therefore s/L, d/L ratios will be identical as a function effective on hydraulic fractures propagation, that is, the K$_1$ value increase with decreasing s/L ratio or increasing d/L ratio and its magnification from onset to propagation increases with decreasing s/L ratio. The scanline is a commonly used method to estimate the fracture distribution on outcrops. The data obtained from the scanline method can be applied to the evaluation of stress field in rock mass.

• Journal of the Korean Wood Science and Technology
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• v.12 no.2
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• pp.20-26
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• 1984

This study was carried out to investigate the influence of chemical type and its retention in the fire-retardant treated plywoods on the static bending strength, a property peculiar to plywood. Being soaked in 20% aqueous solution of $(NH_4)_2SO_4$, $NH_4H_2PO_4$, $(NH_4)_2HPO_4$. Borax-Boric acid and Minalith for 3 to 12 hours at three-hour intervals and redried at $120^{\circ}C$ in hot press, the treated plywoods were put to static bending test. The values of chemical treated plywoods in Stress at proportional limit, Modulus of elasticity, Modulus of rupture and Work per unit volume to proportional limit were widely higher than those of water treated plywoods(control) and Borax-Boric acid treatment showed the highest value in the four mechanical data. And the bending strength of fire-retardant treated plywoods increased with the extension of soaking time or the increase of chemical retention in themselves. Borix-Boric acid was the desirable fire-retardant for thin plywood in view of mechanical strength and soaking defects in this study.

• The Korean Journal of Food And Nutrition
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• v.14 no.1
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• pp.34-39
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• 2001

The purpose of this study was to examine physical properties of the addition of green tea powder on bread flour and dough rheology of white pan bread. Three levels(0.1, 0.5 and 1.0% ) of each green tea powder with bread flour were tested for their effects in dough mixing using rapid disco analyzer, alveogram and farinogram. Addition of green tea powder tended to reduce initial pasting temperature and increase peak viscosity, break down and set back. L(extensibility) and G(swelling index) value in alveogram showed decrement with increasing green tea powder. These meant that the volume of white pan bread would show same tendency. The use of green tea powder increased consistency and water absorption of the bread flour but decreased development time, salability and degree of softening on farinogram. White pan bread with green tea powder had higher value of hardness and springness than without it. Sensory evaluation determined that the white pan bread with 0.5% green tea powder had the highest score.