• Journal of the Korean Wood Science and Technology
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• v.36 no.5
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• pp.42-48
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• 2008

This study was conducted to discuss the effects of hardener and extender contents on peak temperature, reaction enthalpy (${\Delta}H$), gelation time, viscosity change, and pH value in three types of UMF (urea-melamine- formaldehyde) resin with the help of perpHecT LogR meter, differential scanning calorimetry (DSC), and advanced rheometric expansion system (ARES), The results indicated that the pH value of Control A steeply decreased to 5,2 in the early stage but relatively remained constant thereafter as in Synthesis 1 and Synthesis 2, The peak temperature and time decreased as well, whereas ${\Delta}H$ and viscosity increased with the increase of hardener content. On the other hand, ${\Delta}H$ was not changed up to the extender content of 5% and then decreased with its further addition, And the pH value and peak temperature showed no change with the increase of extender content at the hardener content of 5% in three types of UMF resin, The effect of hardener content in this experiment, however, appeared more conspicuous in Control A than in the other two types of Synthesis 1 and Synthesis 2, These results might be caused by higher molecular weight with longer chains of methylene ($-CH_2-$) and methylene ($-CH_2-O-CH_2-$) ether bridges or much more branched chains in Control A.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2013.05a
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• pp.53-55
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• 2013

Nitrite-Type hydrocalumite (calumite) is a material that can provied a self-corrosion inhibition function to the reinforce concrete. In this study, bisphnol A·F type epoxy-midified mortars without hardner contaning calumite is prepared with various polimer-binder ratios, calumite contents and tow types of curing condition, and tested for flexural and compressive strength tensile strength and corrosion-inhibition. As a result, in the case of wet/dry curing condition, strengths of bisphnol A·F type epoxy-modified mortars without hardener contaning calumite is inclined to decrease with increasing of polymer-binder ratio and calumite content. However, dry cured specimens are slightly improved by using bisphnol A·F type epoxy resin. Finally, regardless of polymer-binder ratios and calumite contents, corrosion-inhibition of bisphnol A·F type epoxy-modified mortars without hardener containing calumite is superior than that of unmodified mortar.

• Journal of the Korean Wood Science and Technology
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• v.33 no.2 s.130
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• pp.29-39
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• 2005

Formaldehyde emissions from wood-based panels bonded with pine and wattle tannin-based adhesives, urea-formaldehyde resin (UF), melamine-formaldehyde resin (MF), and co-polycondensed resin of urea-melamine-formaldehyde (UMF) were measured by the Japanese standard method using a desiccator (JIS A 1460) and the EN 120 (European Committee For Standardization, 1991) method using the perforator value. In formaldehyde emission, all particleboards made using the wattle tannin-based adhesive with three different hardeners, paraformaldehyde, hexamethylenetetramine, and tris(hydroxyl)nitromethan (TN), satisfied the requirements of grade $E_1$. But only those made using the pine tannin-based adhesive with the hexamine as hardener met the grade $E_1$ requirements. Hexamine was effective in reducing formaldehyde emission in tannin-based adhesives when used as the hardener. While the UF resin showed a desiccator value of $7.1mg/{\ell}$ and a perforator value of 12.1 mg/100 g, the MF resin exhibited a desiccator value of $0.6mg/{\ell}$ and a perforator value of 2.9 mg/100 g. According to the Japanese Industrial Standard and the European Standard, the formaldehyde emission level of the MDF panels made with UF resin in this study came under grade $E_2$. The formaldehyde emission level was dramatically reduced by the addition of MF resin. The desiccator and perforator methods produced proportionally equivalent results. Gas chromatography, a more sensitive and advanced method, was also used. The samples for gas chromatography were gathered during the experiment involving the perforator method. The formaldehyde contents measured by gas chromatography were directly proportional to the perforator values.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.1
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• pp.80-87
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• 2020

The purpose of this study is to investigate the physical properties and self-healing effects of hardener-free epoxy-modified mortars(EMMs) using ground granulated blast furnace slag(GGBFS). The EMMs with GGBFS were prepared with various polymer-binder ratios and GGBFS contents, and tested for strengths, adhesion in tension, water permeation and self-healing effects. The conclusions obtained from the test results are summarized as follows. The compressive strength of the EMMs with GGBFS is reduced with increasing polymer-binder ratios because of reduction of the degree of hardening in the EMMs, and is somewhat inferior to that of unmodified mortars. In the flexural and tensile strengths, the flexural strength of the EMMs is almost constant with increasing polymer-binder ratios. However, the tensile strength of the EMMs is gradually increased with increasing polymer-binder ratios. Regardless of the GGBFS contents, the adhesion in tension of the EMMs increases sharply with increasing polymer-binder ratios. The water permeation of the EMMs is remarkably reduced with increasing polymer-binder ratios and GGBFS contents. The self-healing effect of the hardener-free EMMs with GGBFS is improved with increasing water immersion period at a GGBFS content of 20%.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.325-330
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• 1999

The objectives of this study were to compare the development of compressive strength of epoxy resin mortars used as repairing materials with respect to maturity, and to propose a predictive model for strength development of epoxy resin mortar. A series of tests were carried out for the hardener contents of 30, 40 and 50 percentage of resin and compressive strength were measured at the of 6, 12, 24, 72, 120 and 168 hours respectively under temperature of 0, 10, 20 and 3$0^{\circ}C$. The datum temperature was estimated by measured strength, and the maturity is calculated with the estimated datum temperature. The compressive strength of epoxy resin mortar could be predicted by regression analysis from the maturity-compressive strength relationship.

• Magazine of the Korean Society of Agricultural Engineers
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• v.42 no.2
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• pp.99-107
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• 2000

The objective of this study are to compare the development of compressive strength of epoxy mortars used as repairing materials with respect to maturity , and to propose a model predicting strength development of epoxy mortars. A series of tests are carried out for the hardener contents of 30, 40 and 50 percentage of epoxy resin and compressive strengths are measured at the age of 6, 12, 24, 72, 120 and 168 hours respectively under the cure temperature of 0, 10, 20 and 3$0^{\circ}C$. The datum temperature is estimated by measured strengths, and the maturity is calculated with the estimated datum temperature. The compressive strength of epoxy mortars can be predicted by regression analysis from the maturity-compressive strength relationship.

• The Journal of the Korea Contents Association
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• v.14 no.4
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• pp.389-396
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• 2014

This study was conducted as the basic research for the replacement of Blast Furnace Slag, Red Mud, Silica Fume, etc., with cement as a solution to the problems arising from the global warming caused by the generation of $CO_2$, and conducted the experimental review to examine the feasibility of matrix having properties identical to those of cement by using the Blast Furnace slag, Red mud, Silica fume, and alkali-activator. For this, by using the the inorganic binder, such as Blast Furnace Slag, Red Mud, Silica Fume, etc., and NaOH, $Na_2SiO_3$ and others as the cement substitute material, the strength characteristic according to the mixture time variation was performed in the tentative experiment. Based on the preceding experiment, this study performed the experiment to analyze the strength properties of hardener through the curing by air-dry temperature, curing by temperature in water, coating curing, and Korean paper curing. For the water curing at $80^{\circ}C$, the compressive strength and flexural strength were found to be the most excellent at the age of the 28th day, and furthermore, it was found that the non-cement hardener could be made, which is considered to affect the production of eco-friendly concrete.

• International Journal of Concrete Structures and Materials
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• v.10 no.4
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• pp.539-553
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• 2016

Polymer concrete (PC) has been favoured over Portland cement concrete when low permeability, high adhesion, and/or high durability against aggressive environments are required. In this research, a new class of PC incorporating Multi-Walled Carbon Nanotubes (MWCNTs) is introduced. Four PC mixes with different MWCNTs contents were examined. MWCNTs were carefully dispersed in epoxy resin and then mixed with the hardener and aggregate to produce PC. The impact strength of the new PC was investigated by performing low-velocity impact tests. Other mechanical properties of the new PC including compressive, flexural, and shear strengths were also characterized. Moreover, microstructural characterization using scanning electron microscope and Fourier transform infrared spectroscopy of PC incorporating MWCNTs was performed. Impact test results showed that energy absorption of PC with 1.0 wt% MWCNTs by weight of epoxy resin was significantly improved by 36 % compared with conventional PC. Microstructural analysis demonstrated evidence that MWCNTs significantly altered the chemical structure of epoxy matrix. The changes in the microstructure lead to improvements in the impact resistance of PC, which would benefit the design of various PC structural elements.

• Journal of the Korean Wood Science and Technology
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• v.31 no.3
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• pp.42-49
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• 2003

The objective of this research was to investigate the possibility of using rice husk flour as a partial substitute for the wood particles used as the raw material for manufacturing particleboards, by examining the physical and mechanical properties of the rice husk flour-wood particleboard as a function of the type of urea-formaldehyde resin used. Commercial wood particles and two types of rice husk flours (A type (30 ㎛), B type (300 ㎛)) were used. E₁ and E₂ class urea-formaldehyde resin was used as the composite binder, combined with 10 wt.% NH₄Cl solution as a hardener. Rice husk flour-wood particleboards with dimensions of 27×27×0.7 (cm) were manufactured at a specific gravity of 0.7 with rice husk flour contents of 0, 5, 10, and 15 (wt.%). We examined the physical properties (specific gravity and moisture content), mechanical properties (three point bending strength and internal bonding) of the composite. In general, it can be concluded that composites made from rice husk flours are of somewhat poorer quality than those made from wood; however, blending in small amounts of rice husk flour (e.g., 5% to 10% by weight) may have no significant impact on quality.

• Nuclear Engineering and Technology
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• v.56 no.4
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• pp.1544-1551
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• 2024

A unique brick series based on Vietnamese clay was manufactured at 114.22 MPa pressure rate for γ-ray attenuation purposes, consisting of (x) metallic waste & (90%-x) red clay mineral & 10% (hardener mixed with epoxy resin), where (x) is equal to the values 0%, 20%, 40%, 50%, and 70%. The impacts of industrial metal waste ratio in the structure and radiation protective characteristics were evaluated experimentally. The increase in metallic waste doping concentrations from 0% to 70% was associated with an increase in the manufactured brick's density (ρ) from 2.103 to 2.256 g/cm³ while the fabricated samples' porosity (Φ) decreased from 11.7 to 1.0%, respectively. Together with a rise in fabricated brick's density and a decrease in their porosities, the manufactured bricks' γ-ray attenuation capacities improved. The measured linear attenuation coefficient (μ, cm^-1) was improved by 30.8%, 22.1%, 21.6%, and 19.7%, at E_γ equal to the values respectively 0.662, 1.173, 1.252, and 1.332 MeV, when the metallic waste concentration increased from 0% to 70%, respectively. The study demonstrates that manufactured bricks exhibit superior radiation shielding properties, with radiation protection efficiencies of 88.4%, 90.0%, 91.7%, 92.1%, and 92.4% for bricks with industrial metal waste contents of 0%, 20%, 40%, 50%, and 70%, respectively, at γ-ray energy (E_γ) of 1.332 MeV.