• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.3
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• pp.199-205
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• 2015

The mechanical and thermal properties of high temperature aluminate cementitious thermal storage materials were investigated in this paper. Alumina cement was used as basic binder and the effect of the replacement of fly ash, silica fume, calcium sulfo-aluminate and graphite for alumina cement was investigated. Experiments were performed to measure mechanical properties including compressive strength before and after thermal cycling, and split tensile strength, and to measure thermal properties including thermal conductivity and specific heat. Test results show that the residual compressive strengths of mixtures with alumina cement only, or alumina cement and silica fume were greater than those of the others. Additionally, the specific heat of mixture with graphite was largest in all the mixtures used in the study. The results of this study could be used to provide realistic information for material properties in thermal energy storage concrete in the future.

• Magazine of the Korea Concrete Institute
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• v.11 no.1
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• pp.141-148
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• 1999

Recently, high performance concrete developed has a good quality at fresh and hardened state, but high binder contents results in spending much money on manufacturing and many cracks by drying and autogenous shrinkage, Therefore, in this paper, not only prevention of cracks caused by drying and autogenous shrinkage, but improvement of quality and accomplishment of economy by applying F.A(fly ash), S.F(silica fume) and CSA(calcium sulfa aluminate) expansive additives as an inorganic admixtures in W/B 35% are discussed. According to the experimental results, when 5% of CSA expansive additives and 15:5(F.A:S.F)are replaced at unit cement content, high performance concrete with both good fluidity at fresh state and high compressive strength, compensation of drying and autogenous shrinkage at hardened state are accomplished.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.601-604
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• 2008

This study as using admixture (G), high early strength agent, calcium hydroxide {a(OH)2} and fine particle cement, etc which have been newly developed for the purpose of quality improvements like the improvement of early strength of concrete that the FA was substituted by 20%, etc, reviewed the possibility of the utilization in the great quantity and the results are summarized as the followings. Slump loss by the kind of mixing material of high early strength agent and Ca(OH)$_2$ showed the smaller width of decrease than that of plain to appear the improved results and fine particle cement and G admixture showed the large slump loss. Air contents were appeared to satisfy the target air contents at all mixing materials. Regarding the compressive strength of the concrete by the kind of mixing material, G admixture was appeared to be highest all on aging 3 days, 7days and 28days at the initial strength. And fine particle cement and high early strength agent showed higher strength increase rate on aging 3days than plain but showed that the increase of strength becomes gradually dulled as aging is increased. And Ca(OH)$_2$ had almost no effect.

• Journal of the Korean GEO-environmental Society
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• v.9 no.5
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• pp.5-13
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• 2008

In this study, It was carried out to evaluate the feasibility of recycled crushed concrete as aggregate used cement mortar replace sand and to investigate engineering properties of recycled aggregate for hazardous waste solidification. The compressive strength of cement mortar replaced 5-15% (wt.) recycled aggregate was over $163kgf/cm^2$ which is the standard of first grade concrete block class C. And cement mortar was examined to evaluate the stability by leaching test. Cu, Cd, Pb, Cr, and As as the heavy metals were proved very stable but mercury (Hg) was leached high concentration because it was simply tied to the cement surface. We investigated the crystal structures of cement mortar and they had shown the peaks of $Ca(OH)_2$, ettringite, and CSH (calcium silicate hydrate). As the result, the longer curing time, the higher CSH peak that means to increase compressive strength and the cement mortar was more stable. Therefore it was shown that it may be possible to apply hazardous waste solidification using recycled aggregate, fly ash and sewage sludge ash.

• Journal of Soil and Groundwater Environment
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• v.22 no.6
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• pp.1-11
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• 2017

This study was conducted to investigate the performance of four commercial chemical agents in stabilizing arsenic (As) in soil at the forest area near the former Janghang smelter site. After amending the stabilizing agents (A, B, C, and D) into As-contaminated soil samples, synthetic precipitation leaching procedure (SPLP) and solubility bioavailability research consortium (SBRC)-extractable As concentrations significantly decreased except for agent D, which is mainly composed of fly ash and calcium carbonate. Increase of SPLP and SBRC-extractable As concentrations in four soil samples (S1, S2, S3, and J2) was attributed to desorption of As adsorbed on iron oxides due to high pH generated by agent D. It is therefore necessary to consider application conditions according to soil characteristics such as pH and buffering capacity. Results of sequential extraction showed that readily extractable fractions of As in soil (i.e., sum of $SO_4-$ and $PO_4-extractable$ As in soil) were converted into non-readily extractable fractions by amending agents A, B, and C. Such changes in the As distribution in soil resulted in the decrease of SPLP and SBRC-extractable As concentration. A series of follow-up monitoring and management plan has been suggested to assess the longevity of the stabilization treatments in the site.

• Journal of the Korea Concrete Institute
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• v.29 no.4
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• pp.415-424
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• 2017

The purpose of this study is to investigate the effect of sulfate (${SO_4}^{2-}$) and magnesium ($Mg^{2+}$) ions on sulfate resistance of Alkali-activated materials using Fly ash and Ground granulated blast furnace slag (GGBFS). In this research, 30%, 50% and 100% of GGBFS was replaced by sodium silicate modules ($Ms(SiO_2/Na_2O)$, molar ratio, 1.0, 1.5 and 2.0). In order to investigate the effects of $Mg^{2+}$ and ${SO_4}^{2-}$, compression strength, weight change, lengh expansion of the samples were measured in 10% sodium sulfate ($Na_2SO_4$), 10%, 5% and 2.5% magnesium sulfate ($MgSO_4$), 10% magnesium nitrate ($Mg(NO_3)_2$), 10% [magnesium chloride ($MgCl_2$) + sodium sulfate ($Na_2SO_4$)] and 10% [magnesium nitrate $(Mg(NO_3)_2$ + sodium sulfate ($Na_2SO_4$)] solution, respectively and X-ray diffraction analysis was conducted after each experiment. As a result, when $Mg^{2+}$ and ${SO_4}^{2-}$ coexist, degradation of compressive strength and expansion of the sample were caused by sulfate erosion. It was found that the reaction of $Mg^{2+}$ with Calcium Silicate Hydrate (C-S-H) occurred and $Ca^{2+}$ was produced. Then the Gypsum ($CaSO_4{\cdot}2H_2O$) was formed due to reaction between $Ca^{2+}$ and ${SO_4}^{2-}$, and also Magnesium hydroxide ($Mg(OH)_2$, Brucite) was produced by the reaction between $Mg^{2+}$ and $OH^-$.

• Journal of the Korean GEO-environmental Society
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• v.15 no.3
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• pp.33-40
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• 2014

In this paper, mechanical and germination characteristics of stabilized dredged soils were investigated to recycle dredged soil in eco-friendly manner such as waterfront construction. Non sintering binder (NSB), which was developed by using interchemical reactions between slag, high-calcium fly ash, alkali activator on the dredged marine clay, was added to dredged soil. Ordinary portland cement was also used for the comparison of two binders. Experimental tests such as flow test and unconfined compressive test were carried out to evaluate characteristics of stabilized dredged soil. Leaching test, pH measure, vegetation germination test were also conducted to consider environmental applicability. The unconfined compressive tests shows that unconfined compressive strength (UCS) also increases with the increase of curing time and mixed ratio. UCS of NSB mixtures were higher than those of OPC mixtures. Germination tests showed that germination and sprouting date are better in NSB mixture than OPC mixture. It can be explained that germination decreased as pH and 7-day strength increased.

• Journal of the Korean Geosynthetics Society
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• v.22 no.3
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• pp.87-95
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• 2023

Recently, redevelopment of the original downtown area is underway, the necessity of construction in adjacent location is increasing. However, excavations in dense urban areas are prone to ground problems due to various causes, so it is necessary to use materials and methods that can minimize such problems. As a general earth retaining method, various methods such as diaphragm wall and CIP method are applied using cement. However, since a large amount of cement is used for the installation of earth retaining method, it is necessary to conduct research on the development of new cement substitute materials to significantly reduce greenhouse gas emissions. In this study, we utilized the hardening reaction of blast furnace slag powder, desulfurized gypsum and high calcium fly ash by alkali activation and applied it to the SCW method. As a result, it was analyzed that the compressive strength of solidified soil using development solidification material was 96.2 ~ 106.3% of OPC at 28 days of curing. In addition, the strength increment ratio was 2.06 for sandy soil and 2.41 for clayey soil, which was higher than 1.85 of OPC. It seems an advantageous in terms of long-term strength. In addition, from the environmental point of view, it was analyzed that there is no elution of heavy metals and that greenhouse gas emissions can be dramatically reduced. Therefore, if further studies are conducted, it can be applied to the SCW method.