• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.5
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• pp.95-102
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• 2022

Recently, there has been a growing interest in reducing greenhouse gases in all industrial fields. In the construction industry, studies have been conducted for the use of high-volume fly ash concrete to replace cement with fly ash. Quantitative measurements of cement hydration and fly ash reactivity enable a clear understanding of the strength development mechanism of high-volume fly ash concrete. It is very difficult to describe the reactivity in a simple way because the hydration and pozzolanic reactions of cement paste containing fly ash are very complex and the composition of the hydration product cannot be accurately determined. This study investigated the hydration and mechanical properties of high volume fly ash (HVFA) cement according to the substitution rate of fly ash (FA). The hydration degree of cement and the reactivity of FA were evaluated through the selective dissolution method and the non-evaporable water content of the paste according to age. In addition, compressive strength was measured using HVFA mortar specimens according to age. As a result of the experiment, as the substitution rate of fly ash increased, the hydration degree of cement increased, but the reactivity of FA decreased.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.3
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• pp.313-319
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• 2017

In general, various factors such as grain size, chemical composition, amorphous amount, amorphous Si and Al content of fly ash affect the reaction with cement. In this study, we investigate the effect of fly ash particle characteristics on compressive strength. The standard sand was pulverized to a particle size similar to that of fly ash and the compressive strength was measured by blending with the cement as in fly. Using the measured compressive strength results, strength enhancement by cement hydration reaction and strength enhancement by particle filling effect were confirmed. Strength increment by pozzolanic reaction of fly ash was calculated by using the compressive strength results of mortar substituted with standard powder. As a result of comparison between compressive strengths and the particle characteristics of fly ash, the blaine showed a weak correlation with the compressive strength and the PI(Pozzolanic Index) showed good correlation with the 10% penetration diameter(D10) and the 50% Respectively. Therefore, it is expected that PI will be a good means to evaluate the fly ash characteristics together with the chemical characteristics of fly ash.

• Journal of the Korea Concrete Institute
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• v.28 no.1
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• pp.49-57
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• 2016

The aim of this study was to investigate the fundamental properties of pyroclastic flow deposit (PFD), and evaluate the fresh and strength properties of concrete mixed with PFD by indoor tests. The fresh properties, strength properties, shrinkage properties, and durability of the concrete mixed with PFD were also evaluated by outdoor plant tests. the harmful alkali-silica reaction did not occur by mixing concrete with PFD. ages. Moreover, no difficulty was found to be associated with concrete manufacture in the plant because no change in air contents and noticeable slump loss occurred by mixing concrete with PFD. The strength properties, shrinkage properties, and durability of the concrete mixed with PFD were also compared with those of normal concrete. With a suitable temperature control and curing method of concrete, the concrete mixed with PFD is considered to be useful in the construction material field.

• Journal of the Korea Institute of Building Construction
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• v.10 no.2
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• pp.59-66
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• 2010

The purpose of this study is to determine the possibilities of blending carbon black, which is known for its permeability as well as its strong heat and fire resistance, into concrete, in a manner that reinforces its strengths mentioned above. Experiments show that in non-solidified, fresh-mixed concrete, the addition of carbon black effectively reduced slump level and air content due to its absorptiveness and minute particle size. It also showed good results in terms of coagulation time, penetration resistance and bleeding level. In solid concrete, it showed better strength than plain concrete. Due to the pozzolanic reaction, its strength became more pronounced over time. At approximately 850 degrees Celsius, the heat and fire resistance level increased in parallel to the level of chemical substitution (by carbon black). Drying shrinkage level appeared to be optimal, and environmental assessment test results related to CO, CO2 and formaldehyde also scored better than plain concrete. In summary, with the appropriate use of AE water-reducing agents, carbon black can prove to be a strong candidate as an ingredient for industry-grade concrete.

• Journal of the Korea Institute of Building Construction
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• v.16 no.2
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• pp.117-123
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• 2016

Glass wool is a material that has been used as a heat insulator in various fields including construction industry. Since it is a nonflammable material, it does not generate toxic gases on fire, and thus public agencies recommend using glass wool as a heat insulator instead of other organic materials. However, repeated drying and wetting cycles can deteriorate thermal property of glass wool due to the shrinkage and reduction in pore size. For this reason, it needs to be replaced periodically, and waste materials are generated. This research aims to utilize waste glass wool as additives for increasing mechanical properties of concrete. According to the experimental results, it was found that glass wool has weak pozzolanic activity, and beneficial effect on both compressive and flexural strength. The optimum amount found in this experimental work was 0.5% volumetric addition to the concrete.

• Journal of the Korea Concrete Institute
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• v.20 no.5
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• pp.619-626
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• 2008

There have been numerous studies to develop eco-friendly concrete. The attempt to reduce the amount of cement usage is suggested as one of the solutions for eco-friendly concrete. To reduce the amount of cement usage, the pozzolan-reaction materials such as ground granulated blast furnace slag, fly ash, and meta kaolin are widely used as the mineral admixture. Hwangtoh which deposited broadly in Korea is a well known eco-friendly material and the activated Hwangtoh with pozzolan-reaction can be practically used as a mineral admixture of concrete. Meanwhile, PET fiber made of recycled PET bottle is a type of recycled material, which can be used to control micro cracks in concrete. But the study about concrete mixed with recycled PET fiber is insufficient and the research of Hwangtoh concrete mixed with PET fiber is urgently needed presently. In this study, experiment and analysis flexural behavior of Hwangtoh concrete blended with recycled PET fiber are carried out. The results are discussed in detail.

• Journal of the Korean Ceramic Society
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• v.33 no.5
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• pp.519-523
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• 1996

Calcium hydroxide produced by cement hydration decreases the durability and the compressive strength of cement mortars. Pozzolanic property of meta kaolin and silica fume allows to avoid this drawback. Calcium hydroxide consumption according to pozzolanic raction is evaluated by Fourier differential thermal analysis. Particulary the properties of high performance and high strength of cement mortar containing above 10% meta kaolin and silica fume were resulted in the pozzolanic activity.

• Journal of the Korea Concrete Institute
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• v.27 no.2
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• pp.127-136
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• 2015

To evaluate the effects of limestone powder and silica fume on the properties of high-strength high-volume ground granulated blast-furnace slag (GGBFS) blended cement concrete, this study investigated the rheology, strength development, hydration and pozzolanic reaction characteristics, porosity and pore size distribution of high-strength mortars with the water-to-binder ratio of 20, 50 to 80% GGBFS, up to 20% limestone powder, and up to 10% silica fume. According to test results, compared with the Portland cement mixture, the high-volume GGBFS mixture had much higher flow due to the low surface friction of GGBFS particles and higher strength in the early age due to the accelerated cement hydration by increase of free water; however, because of too low water-to-binder ratio and cement content, and lack of calcium hydroxide content, the pozzolanic reactio cannot be activated and the long-term strength development was limited. Limestone powder did not affect the flowability, and also accelerate the early cement hydration. However, because its effect on the acceleration of cement hydration is not greater than that of GGBFS, and it does not have hydraulic reactivity unlikely to GGBFS, compressive strength was reduced proportional to the replacement ratio of limestone powder. Also, silica fume and very fine GGBFS lowered flow and strength by absorbing more free water required for cement hydration. Capillary porosities of GGBFS blended mortars were smaller than that of OPC mortar, but the effect of limestone powder on porosity was not noticeable, and silica fume increased porosity due to low degree of hydration. Nevertheless, it is confirmed that the addition of GGBFS and silica fume increases fine pores.

• Journal of the Korean Recycled Construction Resources Institute
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• v.1 no.1
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• pp.49-57
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• 2013

Recently, recycling of industrial by-products and CO2 reduction have been important issues in the world. In this reason, applications and reuse of Fly ash as a binder for concrete, which is generated in thermoelectric power plant, have been one of the effective recycle methods. In order for Fly ash to be applied to concrete, Korean Standard(KS) has selected and managed quality such as $SiO_2$, fineness, specific gravity, ignition loss and activity index. However, there is a limits for activity index, whose test period required is at least 28 days or 91 days. Activity index is the critical indication standard to determine mechanical strength of concrete that contained Fly ash. To complement the disadvantage of test method, this research provided "API test method", which quickly measure Pozzolanic reaction of Fly ash can be considered as a alternative of activity index. Then, the adaptable API test method need to be investigated through comparative analysis with the test result of API, activity index and K-value. The test method can make evaluation of Fly ash quality faster and more accurate. As a result, most Fly ash produced in Korea has not been satisfied in the KS quality standard except water content and specific gravity, and especially fluidized bed boiler ash has its characteristics. Also, API, activity index and K-value have superior interrelationship. The interrelationship between API and activity index and K-value gets increased as the material age gets higher, so API test can be considered as very useful test method for Pozzolanic reaction evaluation of Fly ash.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2013.05a
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• pp.109-110
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• 2013

The purpose of this study was to investigate pozzolanic activity according to the firing temperature of the rice straw ash. In order to measure amount of SiO2 of rice straw ash, XRF(X-ray fluorescence) analysis was tested. Also to evaluate properties of mortars using rice straw ash, mortar flow, cement setting time, compressive strength was tested. As a results, as the mortar with a mixture ratio of rice straw ash up to 15% was found to have a compressive strength superior to that of plain mortar.