• Proceedings of the Korea Crystallographic Association Conference
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• 2002.11a
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• pp.49-49
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• 2002

A strategy for the synthesis of more stable and large periodic mesoporous organo-silica materials has been developed for the 2D hexagonal mesoporous organosilica by the core-shell approach using nonionic PEO-PLGA-PEO triblock copolymer templates. The BET surface area of the solvent-extracted hexagonal mesoporous organosilica is estimated to be 1,016 ㎡/g and the pore volume, pore diameter, and wall thickness are 1.447 ㎤/g, 65 Å, and 43 Å, respectively. More hydrophobic PLGA block than the PPO block used for templates of mesoporous silica proves to be quite effective in confining the organosilicates within the PEO phase. Reaction temperature and acid concentration of an initial solution as well as the chemical nature of the bloc k copolymer templates also demonstrate to be important experimental parameters for ordered organosilica mesophase. Moreover, the mesoporous organosilicas prepared with the PEO-PLGA-PEO block templates maintain their structural integrity for up to 25 days in boiling water at 100℃. The mesoporous materials with large pores and high hydrothermal stability prepared in this study has a potential for many applications.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.11a
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• pp.67-68
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• 2023

This paper reports on the synthesis of paraffin-based phase change materials (PCMs) designed for use in solar reflective paint (SRP) as a thermal energy storage (TES) medium. These PCMs are prepared using the sol-gel process and are encapsulated in silica. The focus of this research is to evaluate the suitability of these synthesized PCMs for efficient thermal energy storage within SRP applications. The obtained PCMs have nanometric dimensions, which make them well-suited for integration into paint formulations. The study also includes a thorough analysis of the chemical, thermal, and structural stabilities of these materials, confirming their applicability in solar reflective paint.

• Advances in materials Research
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• v.11 no.2
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• pp.147-164
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• 2022

This study aims to investigate the influence of scoria aggregate (SA) and silica fume (SF) as a replacement of conventional aggregate and ordinary Portland cement (OPC), respectively. Three types of concrete were prepared namely normal weight concrete (NWC) using limestone aggregate (LSA) and OPC (control specimen), lightweight concrete (LWC) using SA and OPC, and LWC using SA and partial SF (SLWC). The representative workability and compressive strength properties of the developed concrete were evaluated, and the results were correlated with non-destructive ultrasonic pulse velocity and Schmidt hammer tests. The LWC and SLWC yielded compressive strength of around 30 MPa and 33 MPa (i.e., 78-86% of control specimens), respectively. The findings indicate that scoria can be beneficially utilized in the development of structural lightweight concrete. Present renewable sources of aggregate will preserve the natural resources for next generation. The newly produced eco-friendly construction material is intended to break price barriers in all markets and draw attraction of incorporating scoria based light weight construction in Saudi Arabia and GCC countries. Findings of the SWOT analysis indicate that high logistics costs for distributing the aggregates across different regions in Saudi Arabia and clients' resistant to change are among the major obstacles to the commercialized production and utilization of lightweight concrete as green construction material. The findings further revealed that huge scoria deposits in Saudi Arabia, and the potential decrease in density self-weight of structural elements are the major drivers and enablers for promoting the adoption of lightweight concrete as alternative green construction material in the construction sector.

• Elastomers and Composites
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• v.48 no.2
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• pp.114-124
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• 2013

To study the effects of structural difference and fatty acid chain length of glyceride, new dispersion agents having various glyceride structures such as mono-, di-, and tri-, were prepared using glycerol extracted from palm oil and fatty acid having various chain length ranges from 12 to 18. These dispersion agents were mixed with the rubber compounds and compared with conventional metal salt dispersion agents. Glyceride dispersion agent provided remarkable improvement in silica dispersion, compared to metal salt fatty acidic one, even though the viscosity of mixtures was relatively high due to low lubricating effect, and this was approved by mechanical properties, wear properties, and Payne effect. Also, the longer in chain length of fatty acid and the smaller in numbers of fatty acid, the dispersity of silica was improved.

• Structural Engineering and Mechanics
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• v.72 no.3
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• pp.339-354
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• 2019

Reusing building materials and concrete of old buildings can be a promising strategy for sustained development. In buildings, the performance of materials under elevated temperatures is of particular interest for determining fire resistance. In this study, the effect of pozzolan and aggregate type on properties of concrete exposed to fire was investigated. In doing so, nanosilica with cement-replacement levels of 0, 2, and 4% as well as silica fume and ultrafine fly ash with cement-replacement levels of 0, 7.5, and 15% were used to study effect of pozzolan type, and recycled refractory brick (RRB) fine aggregate replacing natural fine aggregate by 0 and 100% was utilized to explore effect of aggregate type. A total of 126 cubic concrete specimens were manufactured and then investigated in terms of compressive strength, ultrasonic pulse velocity, and weight loss at $23^{\circ}C$ and immediately after exposure to 400 and $800^{\circ}C$. Results show that replacing 100% of natural fine aggregate with recycled refectory brick fine aggregate in the concretes exposed to heat was desirable, in that it led to a mean compressive strength increase of above 25% at $800^{\circ}C$. In general, among the pozzolans used here, silica fume demonstrated the best performance in terms of retaining the compressive strength of heated concretes. The higher replacement level of silica fume and ultrafine fly ash pozzolans in the mixes containing RRB fine aggregate led to a greater weight loss rate, while the higher replacement level of nanosilica reduced the weight loss rate.

• New Physics: Sae Mulli
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• v.68 no.11
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• pp.1173-1182
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• 2018

Mesoporous silica allows proper hydration of an ion exchange membrane under low relative humidity due to its strong hydrophilicity and structural characteristic. A mesoporous silica and Nafion composite membrane shows good proton conductivity under low relative humidity. An understanding of ion-channel formation and proton transfer through an ion-channel network in mesoporous silica and Nafion composite membranes is essential for the development and the optimization of ion exchange membranes. In this study, a mesoporous cellular foam $SiO_2/Nafion$ composite membrane is fabricated, and its proton conductivity and performance are measured. Also, the ion-channel distribution is analyzed by using electrostatic force microscopy to measure the surface charge density of the mesoporous cellular foam $SiO_2/Nafion$ composite membrane. The research reveals a few remarkable results. First, the composite membrane shows excellent proton conductivity and performance under low relative humidity. Second, the composite membrane is observed to form ion-channel-rich and ion-channel-poor region locally.

• Structural Engineering and Mechanics
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• v.85 no.2
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• pp.275-287
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• 2023

The use of environmental-friendly building materials is becoming increasingly popular worldwide. Compared to the normal concrete, rubber-based concrete is considered more durable, environmentally friendly, socially and economically viable. In this investigation, M20 grade concrete was designed and the fine aggregates were replaced with crumb rubber of two different micron sizes (0.221 mm and 0.350 mm). Fly ash (FA) and silica fume (SF) replaces the binder as supplementary cementitious materials at a rate of 0, 5, 10, 15, and 20% by weight. The mechanical properties of concrete including compressive strength, tensile, and flexural strength were determined. The polynomial work expectation validates the response surface approach (RSM) concept for optimizing SF and FA substitution. The maximum compressive strength (22.53 MPa) can be observed for the concrete containing 10% crumb rubber, 15% fly ash and 15% silica fume. The reduced unit weight of the rubberized concrete may be attributed to the lower specific gravity of the rubber particles. Two-way ANOVA with a significance criterion of less than 0.001 has been utilized with modest residual error from the lack of fit and the pure error. The predictive model accurately forecasts the variable-response relationship. Since, the crumb rubber is obtained from wasted tires incorporating FA and SF as a cementitious ingredient, it helps to significantly improve mechanical properties of concrete and reduce environmental degradation.

• Journal of Powder Materials
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• v.20 no.4
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• pp.258-263
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• 2013

We examined various ball-milling parameters which affect the structural and morphological modification of multi-wall carbon nanotubes. In particular, the effect of milling mode and the use of different milling agents were examined. Friction milling mode induced more structural changes than impact milling mode except the use of dry ice as a milling agent. Wet milling was helpful for reducing more effectively the agglomeration of nanotubes than dry milling. The use of hard solid particles such as silica and alumina as milling agents resulted in an effective shortening of nanotubes, but often susceptible to the amorphization and the destruction of crystallinity.

• Journal of the Korea Concrete Institute
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• v.27 no.1
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• pp.29-35
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• 2015

Recent studies to develop Very Large Floating Structure(VLFS) has shown that the construction procedure of the structure needs to acquire precast concrete module connection system using prestressing. However, the loads occurring on water are complex combinations of various condition, so the safe and stable performance of the module joints and bonding materials are key to the success of the construction. Therefore, micro-silica mixed aqua-epoxy development was introduced in Part 1 using a bonding material developed in this study. The performance of the micro-silica mixed aqua-epoxy(MSAE) applied joint of concrete module specimens connected by prestressing tendon was evaluated to verify the usability and safety of the material. RC beam, spliced beam connected by prestressing tendon and MSAE, and continuous prestressed concrete beam were tested for their initial cracking and maximum loads as well as cracking procedure and pattern. The results showed that the MSAE can control the stress concentration effect of the shear key and the crack propagation, and the maximum load capacity of MSAE joint specimens are only 5% less than that of continuous RC specimen. The details of the study are discussed in detail in the paper.

• Journal of the Korea Concrete Institute
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• v.24 no.2
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• pp.165-172
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• 2012

In this study, the physical, mechanical, structural, and environmental performances based on field measured data were evaluated to check the suitability of concrete for ecological preservation and cultivation of a hydrophilic environment. More specifically, the study is focused on developing an environmentally friendly functional concrete with river ecology restoration and natural river early formation capabilities. The mechanical performance evaluation results showed that the increase in mix rate of the PVA (Poly Vinyl Alcohol) reinforcement fibers and silica fume caused an increase in the strength. The optimal mix rate was found to be 0.05 volume % PVA fiber and approximately 10% silica fume. The frost resistance evaluation showed that superior performance was gained when 0.05 volume % PVA fiber and 15% silica fume was mixed simultaneously. In the structural performance evaluation, the bending strength was improved by 47.7% compared to plain concrete when mixed with 0.05 volume % PVA fiber. The flexural toughness also saw significant improvement. The environmental monitoring of field performance showed that grasses germinated most rapidly, but the growth of red poppies, a plant that germinates in the spring, was most active with passing of time. Coverage measurements in all of the monitoring locations found favorable coverage of over 95% after 12 weeks. The study results showed that the environmentally friendly functional concrete had outstanding environmental performance.