• Economic and Environmental Geology
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• v.28 no.5
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• pp.519-525
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• 1995

Recently, there have been several cases of serious accidents on concrete structure resulting from rapid deterioration of concrete strength. On the view point of long term stability of concrete, deterioration of concrete strength is mostly due to chemical reaction between alkali and reactive aggregates (alkali-aggreagte reaction; AAR) in concrete rather than a problem of execution. For long-term stability of concrete, concrete aggregates must be carefully selected. Some of rocks used for concrete aggregates contain deleterious minerals reactive to alkali components in concrete. Most of AAR result from chemical reaction between alkali components and reactive silica minerals in aggregates (so called alkali-silica reaction; ASR). The silica minerals are as follows; quartz with seriously distorted lattice structure, volcanic glass, chalcedony, opal, cristobalite, tridymite, etc. ASR may cause expansion and cracks, further collapse in concrete structure, in a few years. In case of crushed aggregates, only a part of rock mass without reactive minerals must be produced in aggregates mine after thorough examination of the distribution of rocks with reactive minerals. In case of natural aggregates, the total content of reactive minerals must be calculated, if, the content is more than 20%, the rate should be lower by mixing other non-reactive crushed- or natural aggregates. If it is obliged to use concrete aggregates all containing deleterious minerals in a discrete area, they must be used with low alkali cement Even if it is low quality in the chemical properties, aggregates with suitable range in the physical properties can be utilized as the aggregate of other purposes.

• Journal of the Mineralogical Society of Korea
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• v.17 no.3
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• pp.277-288
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• 2004

Alkali-silica reaction (ASR) is a chemical reaction between alkalies in cement and chemically unstable aggregates and causes expansion and cracking of concrete. In the Present study, we studied the effects of metakaolin, which is a newly introduced mineral admixture showing excellent pozzolainc reaction property, on the inhibition of ASR. We prepared mortar-bars of various replacement ratios of metakaolin and conducted alkali-silica reactivity test (ASTM C 1260), compressive strength test and flow test. We also carefully analyzed the mineralogical changes in hydrate cement paste by XRD qualitative analysis. The admixing of metakaolin caused quick pozzolanic reaction and hydration reaction that resulted in a rapid decrease in portlandite content of hydrated cement paste. The expansion by ASR was reduced effectively as metakaolin replaced cement greater than 15%. This resulted in that the amounts of available portlandite decreased to less than 10% in cement paste. It is considered that the inhibition of ASR expansion by admixing of metakaolin was resulted by the combined processes that the formation of deleterious alkali-calcium-silicate gel was inhibited and the penetration of alkali solution into concrete was retarded due to the formation of denser, more homogeneous cement paste caused by pozzolanic effect. Higher early strength (7 days) than normal concrete was developed when the replacement ratios of metakaolin were greater than 15%. And also, late strength (28 days) was far higher than normal concrete for the all the replacement ratios of metakaolin. The development patterns of mechanical strength for metakaolin admixed concretes reflect the rapid pozzolanic reaction and hydration properties of metakaolin.

• Structural Engineering and Mechanics
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• v.83 no.1
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• pp.79-92
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• 2022

In this paper, the impact of a vernacular pozzolanic kaolinite mine on concrete alkali-silica reaction and strength has been evaluated. For making the samples, kaolinite powder with various levels has been used in the quality specification test of aggregates based on the ASTM C1260 standard in order to investigate the effect of kaolinite particles on reducing the reaction of the mortar bars. The compressive strength, X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) experiments have been performed on concrete specimens. The obtained results show that addition of kaolinite powder to concrete will cause a pozzolanic reaction and decrease the permeability of concrete samples comparing to the reference concrete specimen. Further, various machine learning methods have been used to predict ASR-induced expansion per different amounts of kaolinite. In the process of modeling methods, optimal method is considered to have the lowest mean square error (MSE) simultaneous to having the highest correlation coefficient (R). Therefore, to evaluate the efficiency of the proposed model, the results of the support vector machine (SVM) method were compared with the decision tree method, regression analysis and neural network algorithm. The results of comparison of forecasting tools showed that support vector machines have outperformed the results of other methods. Therefore, the support vector machine method can be mentioned as an effective approach to predict ASR-induced expansion.

• 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.

• Computers and Concrete
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• v.18 no.2
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• pp.279-295
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• 2016

A new innovative composite material is textile reinforced cementitious composite (TRCC). To achieve high flexural performance researchers suggest polymer modification of TRCC matrices. In this study, nine ready mix repair mortars commonly used in construction industry and the production of TRCC elements were examined. Mechanical properties such as compressive and flexural strength, drying shrinkage were studied. Being a significant durability concern, alkali silica reaction tests were performed according to related standards. Results showed that, some ready repair mortar mixes are potentially reactive due to the alkali silica reaction. Two of the ready mortar mixes labelled as non-shrinkage in their technical data sheets showed the highest shrinkage. In this experiment, researchers designed new matrices. These matrices were fine grained concretes modified with polymer additives; latexes and redispersible powders. Two latexes and six redispersible powder polymers were used in the study. Mechanical properties of fine grained concretes such as compressive and flexural strengths were determined. Results showed that some of the fine grained concretes cast with redispersible powders had higher flexural strength than ready mix repair mortars at 28 days. Matrix composition has to be designed for a suitable consistency for planned production processes of TRCC and mechanical properties for load-carrying capacity.

• Applied Chemistry for Engineering
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• v.7 no.4
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• pp.698-706
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• 1996

Dehydrogenation of methanol to produce formaldehyde was carried out over various silica-alumina catalysts doped with alkali metals in a continuous flow system. The reaction was rather dependent on Lewis acid than Br${\ddot{o}}$nsted acid suggesting that dehydrogenation of methanol was an electronic reaction. The Br${\ddot{o}}$nsted acid sites on silica-alumina were neutralized by doping with alkali metals, and the neutralization effect of Br${\ddot{o}}$nsted acid was dependent on the electron-donating capacity of the dopant metals. Activation energy for dehydrogenation of methanol decreased when Br${\ddot{o}}$nsted acid was neutralized by doping with K.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.49-54
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• 2001

Using waste glass in concrete can cause crack and strength loss by the expansion of alkali-silica reaction(ASR). In this study, ASR expansion and properties of strength were analyzed in terms of brown waste glass content, and fibers(steel fiber, polypropylene fiber) and fiber content for reduction ASR expansion due to waste glass. In this accelerated ASTM C 1260 test of waste glass, pessimum content can not be found. Also, when used the fibers with waste g1ass, there is an effect on reduction of expansion and strength loss due to ASR between the alkali in the cement paste and the silica in the waste glass. Specially, adding 1.5 vol.% of steel fiber to 20% of waste glass the expansion ratio was reduced by 40% and flexural strength was developed by up to 110% comparing with only Waste glass ( $80^{\circ}C$ $H_{2}$ O curing).

• KCI Concrete Journal
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• v.14 no.2
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• pp.76-80
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• 2002

The role of high volume Class F fly ash in reducing expansion due to Alkali-Silica Reaction (ASR) was investigated. A series of modified ASTM C 1260 tests were performed under three different levels of NaOH normality, extending the test period to 28 days, using high- or low alkali cement, and Class F fly ash up to 58 ％ by mass of cement. A reactive siliceous fine aggregate was used. The test results confirm that HVFA replacement in a cementitious system significantly helps in controlling expansion caused by ASR.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.5
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• pp.59-67
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• 2012

During the manufacturing of Portland cement, CO2 gas is also necessarily produced through both decarbonation of calcium carbonate and kiln burning. By partially replacing the Portland cement with limestone powder, which is an inert filler in a concrete mixture, CO2 consumption can be reduced in a construction field. This study is to investigate the fundamental durability characteristics of limestone powder added concrete. Experimental variable was the replacement ratio of limestone powder from 0% to 25% with 5% increment. Durability characteristics were investigated by resistance to freeze-thaw, alkali-silica reaction and de-icing chemical in addition to the properties of fresh concrete. From test results, it was observed that the addition of limestone powder did not significantly affect the resistance to freeze-thaw reaction and de-icing chemical. The addition of limestone powder reduced the occurrence potential of alkali-silica reaction by reducing an alkali content in Portland cement.

• International Journal of Concrete Structures and Materials
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• v.4 no.2
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• pp.119-125
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• 2010

In this study, the effects of the fineness modulus of reactive aggregate on ASR expansion and ASR products have been investigated. The reactive aggregate used was metamorphic aggregate originated from Korea. ASR tests were conducted according to accelerated mortar bar test. The morphology and chemical composition of products formed in mortar bars, 5 years after the mortar bar test had been performed, were studied by scanning electron microscopy equipped with energy dispersive spectroscopy. Test results indicated that ASR expansion of mortar bars decrease in linear proportion to the fineness modulus of reactive aggregate. SEM images indicated that mortar bars showed reactive products formed in cement paste, within air voids and within cracks through particles except for the mortar bar with the fineness modulus of 3.25. The EDS analysis of the reactive products showed presence of silica, calcium and sodium, typical of ASR product composition.