• Macromolecular Research
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• v.13 no.3
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• pp.223-228
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• 2005

In the present work, a low-density polyethylene (LDPE) composite, filled with Zn-ion coated structural silica encapsulated with the diglycidyl ether of bisphenol-A (DGEBA), was synthesized using the conventional melt-blending technique in a sigma internal mixer. The catalytic activity of the Zn-ions (originating from the structural silica) towards the oxirane group (diglycidyl ether of bisphenol-A (DGEBA): encapsulating agent) was assessed by infrared spectroscopy. Two composites, each with a filler content of $2.5 wt\%$ were developed. The first one was obtained by melt blending the Zn-ion coated structural silica with LDPE in a co-rotating sigma internal mixer. The second one was obtained by melt blending the same LDPE, but with DGEBA encapsulated Zn-ion coated structural silica. Epoxy resin encapsulation of the Zn-ion coated structural silica resulted in its having good interfacial adhesion and a homogeneous dispersion in the polymer matrix. Furthermore, the encapsulation of epoxy resin over the Zn-ion coated structural silica showed improvements in both the mechanical and thermal properties, viz. a $33\%$ increase in the elastic modulus and a rise in the onset degradation temperature from 355 to $371^{\circ}C$, in comparison to the Zn-ion coated structural silica.

• Advances in nano research
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• v.15 no.6
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• pp.495-511
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• 2023

In this research, the impact of micro-silica, nano-silica, and polypropylene fibers on the fracture energy of self-compacting concrete was thoroughly examined. Enhancing the fracture energy is very important to increase the crack propagation resistance. The study focused on evaluating the self-compacting properties of the concrete through various tests, including J-ring, V-funnel, slump flow, and T50 tests. Additionally, the mechanical properties of the concrete, such as compressive and tensile strengths, modulus of elasticity, and fracture parameters were investigated on hardened specimens after 28 days. The results demonstrated that the incorporation of micro-silica and nano-silica not only decreased the rheological aspects of self-compacting concrete but also significantly enhanced its mechanical properties, particularly the compressive strength. On the other hand, the inclusion of polypropylene fibers had a positive impact on fracture parameters, tensile strength, and flexural strength of the specimens. Utilizing the response surface method, the relationship between micro-silica, nano-silica, and fibers was established. The optimal combination for achieving the highest compressive strength was found to be 5% micro-silica, 0.75% nano-silica, and 0.1% fibers. Furthermore, for obtaining the best mixture with superior tensile strength, flexural strength, modulus of elasticity, and fracture energy, the ideal proportion was determined as 5% micro-silica, 0.75% nano-silica, and 0.15% fibers. Compared to the control mixture, the aforementioned parameters showed significant improvements of 26.3%, 30.3%, 34.3%, and 34.3%, respectively. In order to accurately model the tensile cracking of concrete, the authors used softening curves derived from an inverse algorithm proposed by them. This method allowed for a precise and detailed analysis of the concrete under tensile stress. This study explores the effects of micro-silica, nano-silica, and polypropylene fibers on self-compacting concrete and shows their influences on the fracture energy and various mechanical properties of the concrete. The results offer valuable insights for optimizing the concrete mix to achieve desired strength and performance characteristics.

• Bulletin of the Korean Chemical Society
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• v.26 no.12
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• pp.1927-1928
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• 2005

• Advances in concrete construction
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• v.11 no.1
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• pp.45-58
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• 2021

Experimental investigation has been conducted to study the effect of using Micro/Nano Silica in presence of steel fibers on improving the static response of reinforced concrete beams. Twenty-one mixtures were prepared with micro silica (MS), Nano silica (NS) and steel fibers (SFs) at different percentages. Cement was replaced by 10% and 15% of Micro silica and 1%, 2% and 3% of Nano silica in the presence of steel fibers at different volume fractions 0%, 1%, and 2%. 258 concrete samples, (126 cubes, 63 cylinders, 63 prisms, and six R.C beams), were investigated experimentally in two stages. The first stage was to investigate the mechanical properties of the prepared mixtures. The second stage was to study the static behavior of R.C beams, using the designed concrete mixtures, under a four-point flexural test. The results showed that replacing cement by (10% MS and 1% NS) produces the optimum mix with a significant improvement in the mechanical properties and the response of R.C beams under static loads. In addition, incorporating steel fibers at different volume fractions have a considerable effect on the flexural toughness of concrete mixes.

• Journal of The Korean Society of Agricultural Engineers
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• v.54 no.5
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• pp.9-16
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• 2012

In this study, the effect of metakaoline and silica fume on the bond performances of structural polyvinyl alcohol (PVA) fiber in cement mortar, including bond strength, interface toughness, and microstructure analysis are presented. Metakaoline and silica fume contents ranging from 0 % to 15 % are used in the mix proportions. Pullout tests are conducted to measure the bond performance of PVA fiber from cement mortar. Test results showed the incorporation of metakaoline and silica fume can effectively enhance the PVA fiber-cement mortar interfacial properties. Bond strength and interface toughness increased with metakaoline and silica fume content up to 10 % in cement mortar and decreased when the metakaoline and silica fume content reached 15 %. The microstructural observation confirms the findings on the interface bond mechanism drawn from the fiber pullout test results.

• Journal of the Korean Ceramic Society
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• v.11 no.1
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• pp.10-18
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• 1974

The hydration at $23^{\circ}C$ between $Ca(OH)_2$ and siliceous materials with various compositions of silica gel and quartz were studied in paste state, and also diatomite was empolyed as another form of silica. The effect of the structural state of silica on the pozzolanic reactivity was investigated by X-ray, DTA, electron microscopy, and chemical analysis. The results obtained were as follows. (1) The molar ratio of $Ca(OH)_2$ to silica gel(C/Sg) being changed in 0.49, 0.81 and 1.22, the free $Ca(OH)_2$ was disappeared within six hours, three days and two weeks respectively and ill-crystallized CSH(I) was formed. However, in the case fo molar ratio of C/Sg=2.45, almost lime was remained uncombinedly after twenty four weeks yet. (2) Though the molar ratio C/Sg of diatomite was 0.71, the hydration was stabilized at three weeks and the result exhibited very peculiar characteristics from silica gel. (3) Pozzolanic reactivity of quartz was negligible, but $\alpha$-cristobalite in diatomite showed appreciable reactivity. (4) The thermal curves showed the exothermic peaks in the range 830 to $930^{\circ}C$ and lower broad peaks at high temperature in the initial steps of hydration, transfered to lower temperature with sharp peaks by proceeding of hydration. (5) The samples containing more silica gel exhibited higher pozzolanic reactivity and martar strength, but the diatomite gave remarkable result for them and they were matched to the strength development rate.

• Membrane Journal
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• v.11 no.3
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• pp.116-123
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• 2001

Polyimide-silica hybrid membranes were prepared and the effect of silica content on the structural properties and the gas transport properties was studied. The hybrid membranes were obtained by the sol-gel process starting from 1,2,4,5-benzenetetracarboxylic dianhydride(PMDA), 4,4`-diamino- diphenyl oxide(ODA) and tetraethoxysilane(TEOS) in N,N` dimethylacetatmide (DMAc) solvent. The structural characterizations of the membrane were performed by FT-IR, EDX, TGA and SEM. The gas permeation experiments with ${N_2}, {O_2}, {H_2}, {CO_2}and ${CH_4}$ were carried out at the temperature of $25^{\circ}C$ and in the range of pressure from 3atm to 7atm. the hybrid membranes showed higher thermal stability than PI membranes. The silica patricles were uniformly embedded in the polyimide matrix and the size of silica particles increased with increasing silica content. The permeability coefficients of ${N_2}, {O_2}, {H_2}, {CO_2}and ${CH_4}$ increased with increasing silica content but the diffusion coefficients might appear to be a result of a solubility enhancement. In spite of the permeability enhancement, an increase in the selectivities of ${H_2}/{N_2}, ${H_2}/{O_2} and ${H_2}/{CO_2} was observed.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.4
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• pp.121-128
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• 2007

The present study evaluates the resistance to sulfate attack of cement matrix with or without silica fume. The main variable was the replacement levels of silica fume. In order to introduce sulfate attack to cement matrix, mortars and pastes was exposed to sodium sulfate solution for 510 days. Visual examination, expansion and compressive strength loss of mortars in addition to characteristics of pore for the paste samples were regularly investigated. From the test results, it was clearly observed that the cement matrix with silica fume was very resistant to sulfate attack irrespective of the replacement levels of silica fume. However, the severe deterioration due to sulfate attack was found in cement matrix without silica fume.

• Advances in concrete construction
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• v.7 no.3
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• pp.143-150
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• 2019

This study presents the fracture properties of nano modified medium strength concrete (MSC). The nano particle used in this study is nano silica which replaces cement about 1 and 2% by weight, and the micro steel fibers are added about 0.4% volume of concrete. In addition to fracture properties, mechanical properties, namely, compressive strength, split tensile strength, and flexural strength of nano modified MSC are studied. To ensure the durability of the MSC, durability studies such as rapid chloride penetration test, sorptivity test, and water absorption test have been carried out for the nano modified MSC. From the study, it is observed that significant performance improvement in nano modified MSC in terms of strength and durability which could be attributed due to the addition pozzolanic reaction and the filler effect of nano silica. The incorporation of nano silica increases the fracture energy about 30% for mix without nano silica. Also, size independent fracture energy is arrived using two popular methods, namely, RILEM work of fracture method with $P-{\delta}$ tail correction and boundary effect method. Both the methods resulted in nearly the same size-independent $G_F$ irrespective of the notch to depth ratio of the same specimen. This shows evidence that either of the two procedures could be used in practice for analysis of cracked concrete structures.

• Bulletin of the Korean Chemical Society
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• v.30 no.11
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• pp.2542-2548
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• 2009

Direct methylation behaviors of 20 amino acids with tetramethylammonium hydroxide (TMAH) were studied under diluted conditions with silica. Amino acid concentration was controlled by dilution with silica ($SiO_2$) and the molar ratios of amino acid/silica were 0.20, 0.50, and 2.0. The molar ratios of amino acid/TMAH (0.51 - 4.64) also varied. It was found that arginine, asparagine, aspartic acid, cysteine, glutamic acid, and glutamine did not generate any directly methylated pyrolysis products, whereas alanine, glycine, isoleucine, leucine, methionine, phenylanaline, valine, and proline generated all the directly methylated pyrolysis products. Tri- and tetra methylated products of lysine consisted of two types. Histidine and threonine hardly generated the partly methylated products. Mono- and dimethylated products of serine, tryptophan, and tyrosine were not observed. Relative intensities of the methylated products varied with the amino acid concentration, TMAH concentration, and pyrolysis temperature. Direct methylation behaviors of amino acids were explained by the structural characteristics of amino acids.