• Journal of the Korea Concrete Institute
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• v.15 no.3
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• pp.497-503
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• 2003

Supplementary cementitious materials (SCM) such as fly ash, ground granulated blast furnace slag and silica fume are now being extensively used in concrete to control expansion due to alkali-silica reactivity (ASR). However, the replacement level of a single SCM needed to deleterious ASR expansion and cracking may create other problem and concerns. For example, incorporating silica fume at levels greater than 10％ by mass of cement may lead to dispersion and workability concerns, while fly ash can lead to poor strength development at early age, The combination of silica fume and fly ash in ternary cementitious system may alleviate this and other concerns, and result in a number of synergistic effects. The aim of the study was to enable evaluation of more realistic suitability of a silica fume-fly ash combination system for ASR resistance based on an in-house modification of ASTM C 1260 test method. The modification can be more closely identified with actual field conditions. In this study three different strengths of NaOH test solution(1N, 0.5N, and 0.25N) were used to measure the expansion characteristics of mortar bar made with a reactive aggregate. The other variable included longer testing period of 28 days instead of a conventional 14 days.

• Journal of Electrical Engineering and Technology
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• v.13 no.5
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• pp.1769-1777
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• 2018

This paper proposes a method for optimal placement of Phasor Measurement Units (PMUs) considering system configuration and its attributes during the planning phase of PMU deployment. Each bus of the system is assessed on four diverse attributes; namely, redundancy of measurements, rotor angle and frequency monitoring of generator buses, reactive power deficiency, and maximum loading limit under transmission line outage contingency, and a consolidated 'degree of criticality' is determined using Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS). The major contribution of the proposed work is the development of modified objective function which incorporates values of the degree of criticality of buses. The problem is formulated as maximization of the aggregate degree of criticality of the system. The resultant PMU configuration extends complete observability of the system and majority of the PMUs are located on critical buses. As budgetary restrictions on utilities may not allow installation PMUs even at optimal locations in a single phase, multi-horizon deployment of PMUs is also addressed. The proposed approach is tested on IEEE 14-bus, IEEE 30-bus, New England (NE) 39-bus, IEEE 57-bus and IEEE 118-bus systems and compared with some existing methods.

• Journal of Korean Society on Water Environment
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• v.32 no.2
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• pp.216-221
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• 2016

The adsorption characteristics of mixed heavy metals (Cr(III), As(VI)) in aqueous solution were investigated using a sediment amendment composite. Sediment amendment composite was composed of clean sediment (40%), zeolite (20%), recycled aggregate (10%), steel slag (10%), oyster shell (10%), and cement (10%). The experimental results showed that the adsorption equilibrium was attained after 180 mins. Heavy metal adsorption was characterized using Freundlich and Langmuir equations. The equilibrium adsorption data for the sediment amendment composite better fitted with the Langmuir model than the Freundlich model. The maximum adsorption capacity of Cr(VI) (36.07 mg/g) was higher than As(III) (25.54 mg/g); and the adsorption efficiency of the Cr(VI) and As(III) ions solution decreased with decreasing pH from 2 to 10. The collective results suggested that the sediment amendment composite is a promising material for a reactive cap that controls the release of Cr(VI) and As(III) from contaminated sediments.

• Bulletin of the Korean Chemical Society
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• v.13 no.5
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• pp.486-491
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• 1992

The rate constants for the reactions of p-nitrophenyl acetate with 6 different aryloxides and 2 benzohydroxamates have been measured spectrophotometrically in water containing various concentrations of cetyltrimethylammonium bromide (CTAB). The reactivity of the nucleophiles has been demonstrated to be significantly enhanced as the concentration of the surfactant increases up to a certain point. When the basicities of the aryloxides are comparable, the rate enhancement is more prominent for the aryloxide having larger binding constant to the micellar aggregate. Benzohydroxamates exhibitis significantly large ${\alpha}$-effect in the absence of the surfactant, although, the ${\alpha}$-effect nucleophiles are considered to be more solvated in water than the corresponding normal nucleophile. Thus, the solvation effect does not appear to be solely responsible for the ${\alpha}$-effect. Interestingly, the large ${\alpha}$-effect disappears in the presence of the surfactant. Therefore, one might attribute the disappearance of the ${\alpha}$-effect to solvent effect. However, a structural change of the reactive ${\alpha}$ -effect nucleophile into unreactive ones would also be considered to be responsible for the absence of the ${\alpha}$-effect in the present system.

• Journal of the Korea Concrete Institute
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• v.20 no.6
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• pp.689-696
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• 2008

The purpose of this study was to evaluate the alkali-silica reactivity for aggregates in Korea according to test methods: accelerated mortar bar test (AMBT) by ASTM C 1260; chemical test by KS F 2545 (ASTM C 289). The results are as follows: The AMBT (ASTM C 1260) results showed that two (2) igneous rocks (two mica granite and felsite), three (3) sedimentary rocks (arkose, red sandstone and shale), two (2) metamorphic rock (slate and vitric tuff), one (1) mineral (quartz) showed more expansion than 0.1% at 14 days. But, some sedimentary rocks and metamorphic rocks expanded more than 0.1% at 28 days even though they were less than 0.1% at 14 days. Therefore, it is necessary to extend the experimental dates more than 14 days to evaluate the possibility of alkali-aggregate reactivity. The chemical test (KS F 2545) results showed that five (5) igneous rocks (andesite, diabase, granite porphyry, muscovite granite and diorite) were indicative of potentially deleterious expansion, while two (2) igneous rocks (diorite porphyry and quartz porphyry) were possible indicative of expansion, and three (3) igneous rocks (biotite granite, two mica granite and felsite) were indicative of innocuous reactivity. The above results showed that the results from chemical method (KS F 2545) and AMBT (ASTM C 1260) had little relationship.

• Magazine of the Korea Concrete Institute
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• v.9 no.1
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• pp.115-121
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• 1997

This study deals with the suppressing characteristics of alkali-silica reaction by ground granulated blast-furnace slag(GGBS) in NaCl solution. NaCl contents used in the experiment ranges over 0%, 2.8% and 20%. Reactive aggregate used is Japanese andesite. Also, three GGBSs of about 4.000. 6, 000 and $8, 000cm^2/g$ were used in the experiment. The replacement proportions of portland cement by GGBSs were 40%. 60%, 70% and 80%. respectively. The specimens with GGBS were severely contracted according to the increasing replacement ratio in NaCl solution. The contraction rate increases according to the increasing in NaCl content. Also. it does with increasing the blaine fineness of GGRS. It is concluded that the suppression of alkali-silica reaction by GGBS in NaCl solution is complished by contraction of GGBS due to chloride ion induced chemical shrinkage.

• Bulletin of the Korean Chemical Society
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• v.23 no.12
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• pp.1773-1777
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• 2002

Reactive oxygen species(ROS) have been investigated to have pivotal roles on amyloidogenecity of $\beta-amyloidpeptide(A\beta)$, the major component of senile plaques in Alzheimer's disease(AD) brain. Addition of radical scavengers is one of the on-going strategies for therapeutic treatment for AD patients. Hsp104 protein including two ATP binding sites from Saccharomyces cerevisiae, as a molecular chaperone, was known to function as a protector of ROS generation when exposed to oxidative stress in our previous study. This observation has led us to investigate Hsp104 protein as a molecular mediator of $A{\beta}$ aggregation in this study. We have developed a new way of expression for Hsp104 protein using GST-fusion tag. As we expected, formation of $A{\beta}$ aggregate was protected by wild type Hsp104 protein, but not by the two ATP-binding site mutant, based on Thioflavin-T fluorescence. Interestingly, Hsp104 protein was observed to keep $A{\beta}$ from forming aggregates independent of ATP binding. On the other hand, disaggregation of $A{\beta}$ aggregates by wild type Hsp104 was totally dependent on the presence of ATP. On the other hand, mutant Hsp104 with two ATP binding sites altered exhibited no inhibition. Another effective antioxidant, hydrazine analogs of curcumin were also effective in $A{\beta}$ fibrilization as protectors against oxidative stress. Based on these observations we conclude that Hsp104 and curcumin derivatives, as protectors of oxidative stress, inhibit $A{\beta}$ aggregation in virto and can be candidates for therapeutic approaches in cure of some neurodegenerative disease.

• Computers and Concrete
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• v.24 no.6
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• pp.541-553
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• 2019

Alkali-silica reaction (ASR) in concrete can induce degradation in its mechanical properties, leading to compromised serviceability and even loss in load capacity of concrete structures. Compared to other properties, ASR often affects the modulus of elasticity more significantly. Several empirical models have thus been established to estimate elastic modulus reduction based on the ASR expansion only for condition assessment and capacity evaluation of the distressed structures. However, it has been observed from experimental studies in the literature that for any given level of ASR expansion, there are significant variations on the measured modulus of elasticity. In fact, many other factors, such as cement content, reactive aggregate type, exposure condition, additional alkali and concrete strength, have been commonly known in contribution to changes of concrete elastic modulus due to ASR. In this study, an artificial intelligent model using artificial neural network (ANN) is proposed for the first time to provide an innovative approach for evaluation of the elastic modulus of ASR-affected concrete, which is able to take into account contribution of several influence factors. By intelligently fusing multiple information, the proposed ANN model can provide an accurate estimation of the modulus of elasticity, which shows a significant improvement from empirical based models used in current practice. The results also indicate that expansion due to ASR is not the only factor contributing to the stiffness change, and various factors have to be included during the evaluation.

• Journal of the Korea Concrete Institute
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• v.17 no.1 s.85
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• pp.129-137
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• 2005

In Korea, due to the insufficiency of natural aggregates and increasing needs of crushed stones, it is necessary to examine the alkali-silica reaction of the crushed stones. The reaction produces an alkali-silica reaction gel which can imbibe pore solution and swell to generate cracks that are visible In affected concrete. In general, crushed stones are tested by petrograptuc examination, chemical method and mortar-bar method, but the most reliable method Is mortar-bar test. This study tested alkali-silica reactivity of crushed stones of various rock types using ASTM C 227 and C 1260, and compared the results of two test methods. This study also analyzed effects of particle size and grading of reactive aggregate on alkali-silica reaction expansion of mortar-bar. The effectiveness of mineral admixtures to reduce detrimental expansion caused by alkali-silica reaction was investigated through the ASTM C 1260 method. The mineral admixtures used were nv ash, silica fume, metakaolin and ground granulated blast furnace slag. The replacement ratios of 0, 5, 10, 15, 25 and $35\%$ were commonly applied for all the mineral admixtures and the replacement ratios of 45 and $55\%$ were additional applied for the admixtures that could maintain workability. The results indicate that replacement ratios of $25\%$ for ay ash, $10\%$ for silica fume, $25\%$ for metakaolin or $35\%$ for ground granulated blast furnace slag were most effective to reduce alkali-silica reaction expansion under the experimental conditions.