• Journal of the Korean Geotechnical Society
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• v.30 no.1
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• pp.93-101
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• 2014

In this study, a blast furnace slag having latent hydraulic property with an alkaline activator for resource recycling was used to solidify sand without using cement. Existing chemical alkaline activators such as $Ca(OH)_2$ and NaOH were used for cementing soils. An alkaliphilic microorganism, which is active at higher than pH 10, is tested for a new alkaline activator. The alkaliphilic microorganism was added into sand with a blast furnace slag and a chemical alkaline activator. This is called the microorganism alkaline activator. Four different ratios of blast furnace slag (4, 8, 12, 16%) and two different chemical alkaline activators ($Ca(OH)_2$ and NaOH) were used for preparing cemented specimens with or without the alkaliphilic microorganism. The specimens were air-cured for 7 days and then tested for the experiment of unconfined compressive strength (UCS). Experimental results showed that as a blast furnace slag increased, the water content and dry density increased. The UCS of a specimen increased from 178 kPa to 2,435 kPa. The UCS of a specimen mixed with $Ca(OH)_2$ was 5-54% greater than that with NaOH. When the microorganism was added into the specimen, the UCS of a specimen with $Ca(OH)_2$ decreased by 11-60% but one with NaOH increased by 19-121%. The C-S-H hydrates were found in the cemented specimens, and their amounts increased as the amount of blast furnace slag increased through SEM analysis.

• Journal of the Korea Concrete Institute
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• v.24 no.6
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• pp.651-658
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• 2012

This paper concentrates on the evaluation of microcracks in thermal damaged concrete on the basis of the nonlinear ultrasonic modulation technique. Since concrete structure exposed to high temperature accompanies the development of microcracks due to the physical and chemical changes from temperature and exposed time, the adoption of nonlinear approach is required. Instead of using the conventional ultrasonic nondestructive methods which have the limitation in evaluating excessive microcracks, accordingly, a nonlinear ultrasonic modulation method which shows better sensitivity in quantifying microcracks is introduced. Upon the analysis for the modulation of ultrasonic wave and low frequency impact to measure the nonlinearity parameter, which can be used as an indicator of thermal damage, the verification processes for the introduced technique are followed: SEM investigation and permeable pore space test are performed to characterize thermally induced microcracks in concrete, and ultrasonic pulse velocity tests are performed to confirm the outstanding sensitivity of nonlinear ultrasonic modulation technique. In advance, compressive strength of thermal damaged concrete is measured to represent the effect of microcracks on performance degradation. Correlation studies between experimental data and measured data show that nonlinear ultrasonic modulation technique can effectively be used to quantify thermally induced microcracks, and to estimate the compressive strength of thermally damaged concrete.

• Korean Chemical Engineering Research
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• v.50 no.5
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• pp.789-794
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• 2012

For the purpose of development of the latex suitable for polymer cement mortar, experiments on the preparation of carboxylated styrene butadiene latex by the method of the two-step emulsion polymerization were performed. Methyl methacrylate, methacrylic acid and acrylic acid were selected as carboxylic co-monomer, styrene and butadiene as monomer, sodium dodecylbenzene sulfonate and sodium salt of lauryl sulfonate as anionic emulsifiers, and nonylphenoxy poly (ethyleneoxy) ethanol (n=10, 20, 40) as latex stabilizer. Potassium persulfate and sodium bisulfite were also used as redox initiator, and sodium monohydrogen phosphate and potassium carbonate as electrolytes. The effects of categories and concentration of carboxylic co-monomer, molecular weight control agent, crosslinking agent, and styrene/butadiene monomer ratio on the characteristics of latex were investigated. Polymerization recipes for preparation of polymer cement mortar could be proposed. The prepared latexes were tested for the physical properties such as compressive and flexural strength when latexes were mixed with cement mortar. The results showed that the latex could be adapted to polymer cement mortar. Also, it was recognized that the compressive and flexural strength were exhibited 25.4% and 45.3% respectively higher improvement than the quality standards at 28 days curing time.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.3
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• pp.147-152
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• 2010

In this study, the artificial coarse aggregate was manufactured by using coal ash and low grade clay. The characteristics of a coal ash-clay system were investigated using XRD, XRF, TG-DTA, SEM and Dilatometer with various coal ash contents. The chemical compositions are the fly ash, bottom ash and clay, $Al_2O_3$ are 28.5 wt%, 32.4 wt% and 18.1 wt%, and $SiO_2$ are 33.0 wt%, 53.7 wt% and 68.4 wt% in weight ratio, respectively. The shrinkage of specimens started at around $850^{\circ}C$ and changed little up to $1100^{\circ}C$, but increased markedly at above $1100^{\circ}C$. The shrinkage rate is strongly related to the decarbonization amount of coal ash. At the sintering temperature $1150^{\circ}C$, it was found that quartz, mullite, anorthite and albite phase exist in all specimens. It was found that bottom-clay system specimen sintered at $1150^{\circ}C$ had a good compressive strength of 87.5 kg/$cm^2$, and the compressive strength of bottom-clay specimen was higher than that of fly-clay system specimen. The reusability of coal ash as a raw material in the process of shotcrete resources such as artifical coarse aggregate is highly expected.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.1
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• pp.97-104
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• 2020

The present study conducted mock-up tests under the simulated sewage environments to examine the practical significance and limitation of coating materials that were previously developed on the basis of the bacterial glycocalix as a protection of concrete structures exposed to microbiological and sulphate attacks. The variations of the compressive strength and mass of the concrete due to the sulphate attack were measured using cylinder specimens. The bacteria growth and glycocalix formulation were calculated from the samples extracted from the sewage pipes. The next generation sequencing analysis was also conducted for environmental damage assessment due to the use of Rhodobacter capsulatus in the simulated sewage environments. The mock-up tests revealed that the developed coating materials have a good potential in resisting the sulphate attack, indicating no reduction on compressive strength and mass of the coated concrete under the sewage environment. At the age of 91 days, the concentrations of viable bacteria and glycocalix measured from the hardened coating materials were 1.4×10⁴cell/mL and 67.5mg/㎤, respectively. Moreover, harmful strains were not observed in the sewage water including glycocalix-coated concrete pipes. This implies that Rhodobacter capsulatus used in the coating materials does not influence negatively the microorganism cluster in the sewage environments.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.5
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• pp.12-20
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• 2017

This report presents the results of an investigation on the fundamental properties of mortars high fluidity high volume slag cement(HVSC) activated with sodium silicate($Na_2SiO_3$). The ordinary Portland cement(OPC) was replaced by ground granulated blast furnace slag(GGBFS) from 40% to 80% and calcium sulfoaluminate(CSA) was 2.5% or 5.0% mass. The $Na_2SiO_3$ was added at 2% and 4% by total binder(OPC+GGBFS+CSA) weight. A constant water-to-binder ratio(w/b)=0.35 was used for all mixtures. The research carried out the mini slump, V-funnel, setting time, compressive strength and drying shrinkage. The experimental results showed that the contents of superplasticizer, V-funnel, setting time and drying shrinkage increased as the contents of CSA and $Na_2SiO_3$ increase. The compressive strength increases with and an increase in CSA and $Na_2SiO_3$. One of the major reason for these results is the accelerated reactivity of GGBFS with CSA and $Na_2SiO_3$. The maximum performance was CSA 5.0% + $Na_2SiO_3$ 4% specimens.

• Korean Journal of Agricultural Science
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• v.31 no.2
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• pp.105-114
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• 2004

This study was performed to examine the physical and mechanical properties of eco-concrete using soil, natural coarse aggregate, soil compound and polypropylen fiber. The mass loss ratio was decreased with increasing the content of coarse aggregate and soil compound. The compressive strength, flexural strength, ultrasonic pulse velocity and dynamic modulus of elasticity were increased with increasing the content of coarse aggregate, soil compound and polypropylene fiber. The compressive and flexural strengths were showed in 8.07 MPa and 2.641 MPa at the curing age 28 days, respectively. The coefficient of permeability was decreased with increasing the content of coarse aggregate and soil compound, but it was increased with increasing the content of polypropylene fiber. The lowest coefficent of permeability was showed in $5.066{\times}10^{-9}cm/s$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.6
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• pp.257-262
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• 2015

Recently the world wide efforts reduce occurrence of $CO_2$; global warming main reason. The aim of this study is to improve recycling rate of the fly ash (FA) and fused waste slag (FWS) from the power plant and to carbonate under supercritical condition ($40^{\circ}C$, $80kgf/cm^2$ pressure, 60 min) for $CO_2$ fixation. Specimens of mortar with various mixing ratios of FA, FWS (from 100:0 to 20:80 in 5 steps of 20 % reduction each time), distilled water and 3 M NaOH alkali activators were prepared. As a result, the proportion of weight change ratio increases with CaO content, to 12 % after carbonation under the supercritical condition. There is difference of compressive strength between the carbonated and the alkali activator mortar specimens. The stabilization of $CO_2$ fixation through carbonation which could confirm the applicability of the eco-friendly materials without loss of compressive strength.

• Journal of the Korea Institute of Building Construction
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• v.9 no.5
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• pp.63-70
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• 2009

This study is part of an ongoing research project on the development of a sound-absorbing lightweight foamed concrete manufactured by a hydro-thermal reaction between silica and calcium. As the silica source, pulverized bottom ash was used, and as several cementitious powders of ordinary portland cement, alumina cement and calcium hydroxide were used. Manufacture of foamed concrete was accomplished using the pre-foaming method to make a continuous pore system, which is the method of making the foam by using a foaming agent, then making the slurry by mixing the foam, water, and powders. The experiment factors are W/B, foam agent dilution ratio, and foam ratio, and test items are compressive strength, dry density, void ratio, and absorption rate, as evaluated by NRC. The experiment results showed that the sound absorption of lightweight foamed concrete satisfied NRC requirements for the absorbing materials in most of the experiments. It is thus concluded that foam ratio was the most dominant factor, and significantly affected all properties of lightweight foamed concrete in this study. W/B rarely affected total void ratio and continuous void ratio as well as compressive strength, and dry density and foam agent dilution ratio also had little effect onalmost all properties. The analysis of the correlation between NRC, absorption time, continuous void ratio, and absorption time showed that the interrelationship of the continuous void ratio was high.

• Journal of the Korea Concrete Institute
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• v.27 no.4
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• pp.427-434
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• 2015

The objective of this study is to establish an rational mixture-proportioning procedure for low-$CO_2$ concrete using supplementary cementitious materials (SCMs) achieving the targeted $CO_2$ reduction ratio as well as the conventional requirements such as initial slump, air content, and 28-day compressive strength of concrete. To evaluate the effect of SCM level on the $CO_2$ emission and compressive strength of concrete, a total of 12537 data sets were compiled from the available literature and ready-mixed concrete plants. The amount of $CO_2$ emission of concrete was assessed under the system boundary from cradle to concrete production stage at a ready-mixed concrete plant. Based on regression analysis using the established database, simple equations were proposed to determine the mixture proportions of concrete such as the type and level of SCMs, water-to-binder ratio, and fine aggregate-to-total aggregate ratio. Furthermore, the $CO_2$ emissions for a given concrete mixture can be straightforwardly calculated using the proposed equations. Overall, the developed mixture-proportioning procedure is practically useful for determining the initial mixture proportions of low-$CO_2$ concrete in the ready-mixed concrete field.