• Journal of the Korea Institute of Building Construction
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• v.15 no.1
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• pp.25-33
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• 2015

In this study, initial crack index was evaluated by FEM analysis to find the crack propagation from hydration heat in precast concrete. As results, as the usage of hardening accelerator increased, initial compressive strength increased and setting time was shortened. Additionally, as amounts of hardening accelerators increased, the central temperature of concrete increased and the time to reach the highest temperature was shortened. It was demonstrated that the hardening accelerators accelerated the hydration reaction of cement, and caused the increase of hydration heat within the short period of time. Furthermore, the crack index for evaluating the heat level was performed by FEM. As results, there was no problem about the cracks, despite of the growth of initial high hydration heat. This is because of the increased tensile strength that is large enough to sustain the thermally induced-stress.

• Journal of Food Hygiene and Safety
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• v.28 no.3
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• pp.195-201
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• 2013

In atherosclerosis, blood vessels become sensitive to vessel-constricting agents leading to reduced control in the event of abrupt blood pressure changes. Mulberry trees (Morus alba L., MA) have been claimed to contain various bioactive principles that could possibly prevent atherosclerosis development caused by high cholesterol consumption. In order to examine whether MA feeding can prevent the sensitization of blood vessels, MA leaves were fed to rats for 8 weeks and pressor responses to vasoconstricting agents were assessed. Animals were pithed before blood pressure assessments to eliminate reflex compensation in vessel responses. Feeding diets containing high levels of cholesterol led to potentiated pressor responses to sympathetic nerve stimulation, or to injection of norepinephrine, phenylephrine, angiotensin II and vasopressin in pithed rats. These potentiated pressor responses were prevented in rats fed MA leaf-containing diets at 2 or 10% levels. It was also examined in anesthetized non-pithed rats whether similar cholestrol-related sensitization and MA prevention could be observed. However, high cholesterol-induced sensitization in pressor responses were not observed, suggesting that destruction of central cardiovascular control by pithing must have revealed the sensitization responses. It was concluded that MA leaves seem to be active in preventing abnormal blood vessel reactivity caused by hypercholesterolemia.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.2
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• pp.1-5
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• 2000

The silane compounds as a coupling agent have been used in the propellant in order to enhance the mechanical property and lower the viscosity. They showed great effects in the PEG propellant. In PCP propellant, however, the silane compounds not only made a severe cure problem but also deteriorated the mechanical property. In this study, TESPN as a silane compound was applied in PEG and PCP binder for finding above factors. The main reason was that the main chains of PCP were broken due to the trans-esterification reaction of ester groups in PCP and alchol which was produced by reacting silane compounds and moisture in the solution of liquid binder.

• Korean Chemical Engineering Research
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• v.52 no.1
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• pp.63-67
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• 2014

The effects of reactant composition on the particle size distribution, synthetic yield, and density of Phenol-formaldehyde bead were examined in the synthesis of resol-type phenolic resin. Decrease of the content of DI water as dispersion media can increase the viscosity of suspension, which may cause the difference of particle size distribution and aggregation. The average particle size of synthesized beads was also decreased with the increasing content of stabilizer which can affect the interfacial area. The amount of crosslinking agent showed no effect on the size distribution and synthetic yield, but it made a decrease in the density of synthesized bead due to the macropore in the bead.

• Journal of the Korea Concrete Institute
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• v.14 no.3
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• pp.349-356
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• 2002

This research deals with the properties of fresh and hardened high-performance concrete(HPC) incorporating high-reactivity metakaolin(HRM). The properties of fresh and hardened state concrete were investigated included air content, slump flow, setting time, heat of hydration, compressive strength, resistance to chloride-ion penetration, abrasion and repeated freezing and thawing. The properties of the HRM concrete were also compared with those of the portland cement concrete and silica fume(SF) concrete. The laboratory test results indicate that HRM material can be used as a supplementary cementitious material to produce high-performance concrete.

• Applied Chemistry for Engineering
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• v.3 no.4
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• pp.627-638
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• 1992

PPG and BPA-type polyurethane prepolymers(NCO terminated) were obtained from bisphenol A and four types of PPG, having different molecular weight and numbers of functional groups. PPG and BPA-type polyurethane dimethacrylates were synthesized by reacting PPG and BPA-type polurethane prepolymer with 2-HEMA respectively. PPG-type polyurethane dimethacrylates were formulated with initiator(CHP), inhibitor(hydroquinone) and reactive diluent(TEGDMA). The effect of formulation on the torque changes was studied. Four kinds of PPG-type polyurethane dimethacrylates, having different molecular weight and numbers of functional group, were formulated with the same amount of CHP, TEGDMA and hydroquinone. The effects of the molecular weight of PPG-type polyurethane dimethacrylate and functional group numbers of PPG-type polyurethane dimethacrylates on the torque were investigated. These results showed that the torque of PPG-type polyurethane dimethacrylates, having same numbers of functional group, increased with decreasing molecular weight of dimethacrylates and torque of PPG-type polyurethane dimethacrylate, having similar molecular weight, was increased with increasing the number of fuctional group. The glass-transition temperature(Tg) of gels obtained by thermosetting cure for the four kinds of PPG-type polyurethane dimethacrylates were measured by DSC and molecular weights between cross-links(Mc) were calculated from Tg changes.

• Korean Journal of Food Science and Technology
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• v.27 no.2
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• pp.205-209
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• 1995

Edible hardened soybean oil is processed by hydrogenation of refined soybean oil in order to upgrade the heat and oxidation stability and to improve flavor and physical nature. This study aims to investigate the influences of various reaction conditions on iodine value, fatty acid composition and trans isomer formation in hydrogenating soybean oil. In case that hardening temperature is $180^{\circ}C$, trans acid formation increased by 6.2 times more under $3.0{\;}kg/cm^{2}H_{2}$ than under $0.5{\;}kg/cm^{2}H_{2}$, while linolenic acid decreased in contents. In case of $200^{\circ}C$ of hardening temperature trans acid formation showed 4.6% higher under $0.5{\;}kg/cm^{2}H_{2}$ than under $3.0{\;}kg/cm^{2}H_{2}$ while contents of linolenic and linoleic acids showed 0.51% and 2.5% lower respectively. It is concluded that $200^{\circ}C$ of hardening temperature under 0.5 and $3.0{\;}kg/cm^{2}H_{2}$ is better condition because trans isomers are little produced, and iodine value and linolenic acid content decreased in hardening soybean oil.

• Resources Recycling
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• v.3 no.3
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• pp.27-31
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• 1994

We tested the limestone sludge produced in Pohang Iron & Steel Co., Ltd. as a filler powder for the effective use of portland cement. Hydration process was investigated by measuring the hydration rate, the amounts of non-evaporable water and compressive strength of cement-limestone sludge paste prepared by mixing limes-tone sludge with cement. The results obtained in this study can be summarized as follows: 1. There is no significant difference between the cases of adding up to 10% limestone sludge and those of unmixed cement system. However the reaction rate increases in the 5% limestone sludge system(due to the effects of fine). 2. The compressive strength increases proportionally with increasing the measured amount of non-evaporable water, Adding 5% limestone sludge also increases the strength a little higher, and the compressive strength and calcium silicate hydrates. In the case of the mixed limestone sludge, $2\theta$=$11.7^{\circ}$ peak appears in the samples of 28 days hydration. This peak indicted the presence of calcium carboaluminate hydrate. Although limestone sludge is generally regarded as a inert materials, some kinds of cement can produce a calcium carboaluminate by reacting with aluminate in cement pastes.

• Polymer(Korea)
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• v.25 no.1
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• pp.15-24
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• 2001

In this study, the effects of different glycol molar ratios of unsaturated polyester(UPE) resins on the curing behaviors were investigated. The cross linking process was checked or monitored by differential scanning calorimetry(DSC) and by viscoelastic properties of rigid-body pendulum model. The knife-edge from which the pendulum is suspended, is immersed in a reaction mixture, and the change of the viscoelastic behavior brings on those of the period(T) and logarithmic decrement(${\Delta}$) of the damped free oscillations of the pendulum. The values of T and ${\Delta}$ obtained are related to the dynamic modulus(E') and modulus loss(E'). The information on the viscoelastic behavior of unsaturated polyester(UPE) resins during the curing process are shown to illustrate the usefulness of the techniques. As the content of NPG in a propylene glycol(PG)/NPG glycol mixture increased, both the cycle time during cure and the change of damping during cure of UPE resin decreased.

• Polymer(Korea)
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• v.26 no.5
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• pp.599-606
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• 2002

In this study, 4,4'-tetraglycidyl diaminodiphenyl methane (TGDDM)/polyamideimide (PAI) blends were cured using diaminodiphenyl sulfone (DDS). And the effect of addition of different PAI contents to neat TGDDM was investigated in the thermal, mechanical, and morphological properties of the blends. The cure behavior and thermal stability of the cured specimens were monitored by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. Also, the critical stress intensity factor (K$\_$IC/) was measured in UTM, and the phase separation behavior and final morphology of TGDDM/PAI blends were examined in scanning electron microscopy(SEM). As a result, the cure temperature and cure activation energy (E$\_$a/) were decreased with increasing the PAI content. The decreasing of cure temperature and cure activation energy were probably due to the presence of secondary amine group of PAI backbone used as co-initiator. But, the decomposition activation energy (E$\_$t/) and K$\_$IC/ value were increased up to 5. 10 phr of PAI content, respectively and they were decreased above the PAI contents. These results were explained on the basis of chain scission reaction by etherification. And morphology of blends observed from SEM was confirmed in co-continuous structures.