• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.1
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• pp.66-73
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• 2019

Approximately 80% of the mines are vacated or abandoned mines and are mostly left without suitable environmental treatment facilities. In the area around the abandoned mine site, problems such as drainage of acidic city drainage and leakage of leachate occur, and ground subsidence caused by this can cause a safety accident due to sink hole occurrence. In this study, flow, compressive strength, water uptake, pore and hydration characteristics were investigated to investigate the basic properties of liner and cover material based on the replacement ratio of nano silica and silica fume in the existing blast - furnace slag fine powder. As a result, as the substitution ratio of nano silica and silica fume increased, the flow and compressive strength of nano silica specimens increased and the absorption rate decreased. In the case of pore characteristics, the amount of pores decreased as the substitution ratio of nano silica and silica fume increased. Especially, the capillary porosity of 10-1,000 nm diameter decreased. Ray diffraction analysis and SEM measurement showed that the peak positions of the hydration products were almost the same when compared with the 5% alternative test samples of Plain and silica fume.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.4
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• pp.443-450
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• 2021

The effects of blast furnace slag(BFS) and desulfurized gypsum(FDG) on the compressive strength of CFBA, and self-hydration of CFBA were studied. CFBA has self-hydrating and hardening properties, and it can be seen that the compressive strength of CFBA can be improved by using appropriate amounts of BFS and FDG. In addition, the self-hardening properties of CFBA are similar to the hydration reaction of 4CaO·Al₂O₃·Fe₂O₃ (C₄AF), a cement clinker mineral, and when free-CaO, CaSO₄ and CaCO₃ coexist, Compressive strength of CFBA is expressed by the formation of calcium carbo compounds and hydrates of ettringite, calcium silicate, and calcium aluminate.

• Journal of the Korea Concrete Institute
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• v.23 no.5
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• pp.609-615
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• 2011

MgO concrete containing lightly burnt MgO powder at $850{\sim}1,000^{\circ}C$ may have a long-term expansibility characteristic. Such expansibility of MgO concrete can compensate the shrinkage at later ages since the hydration of the MgO is very slow. However, the addition of MgO delays the initial hydration of cement and increases the setting time of cement. Also, the porosity and pore-size distribution of the MgO concrete are different from OPC concrete. Therefore, in order to use MgO in practice, both mechanical and durability properties of MgO concrete should be carefully examined. In this study, durability tests on carbonation, freezing-thawing, and diffusion of chloride were carried out after 56 days of underwater curing at $20^{\circ}C$ to compare durability characteristics of 5% MgO-mixed concrete with those of OPC concrete. The results showed that MgO concrete shows a greater durability than the concrete with no MgO, because the micro structure in the MgO concrete is much denser due to its expansibility characteristic.

• Journal of the Korea Institute of Building Construction
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• v.14 no.5
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• pp.389-396
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• 2014

The set accelerator used for shotcrete at high pH environment often causes the dusting problem in practice. In this research, a slurry-type set accelerator was developed to avoid this problem and its effectiveness was investigated by applying it to shotcrete mortars. Set time, stiffening, compressive strength, and chloride ion penetration resistance were examined with different amounts of slag, used as partial replacement of cement. According to the experimental results, it was found that the earlier responses such as set time, stiffening, and 1-day compressive strength were probably affected by the amount of ettringite, formulated by the hydration between C12A7 and calcium sulfate polymorphs present in blast furnace slag. Whereas, it is believed that the result of compressive strength after 3 days was attributed to the hydration of tricalcium silicates. As for the results of a chloride ion penetration test, the partial replacement of cement with slag significantly reduced the total charge passed through the shotcrete mortar.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.4
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• pp.96-102
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• 2019

When GGBFS(Ground Granulated Blast Furnace Slag) with high blaine is incorporated in concrete, compressive strength in the initial period is improved, but several engineering problems arise such as heat of hydration and quality control. In this paper, compressive strength and durability performance of concrete with 3,000 Grade-low fineness slag are evaluated. Three conditions of concrete mixtures are considered considering workability, and the related durability tests are performed. Although the strength of concrete with 3,000 Grade slag is slightly lower than the OPC(Ordinary Portland Cement) concrete at the age of 28 days, but insignificant difference is observed in long-term compressive strength due to latent hydration activity. The durability performances in concrete with low fineness slag show that the resistances to carbonation and freezing/thawing action are slightly higher than those of concrete with high fineness slag, since reduced unit water content is considered in 3,000 Grade slag mixture. For the long-term age, the chloride diffusion coefficient of the 3000-grade slag mixture is reduced to 20% compared to the OPC mixture, and the excellent chloride resistance are evaluated. Compared with concrete with OPC and high fineness GGBFS, concrete with lower fineness GGBFS can keep reasonable workability and durability performance with reduced water content.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.3
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• pp.294-301
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• 2020

This study evaluated the burnability and hydration reaction of clinker burned with high Al₂O₃ content OPC to apply large amounts of industrial by-products in the cement manufacturing process. Specifically, after preparing a clinker with a high C₃A content by burning the OPC raw material with a high content of Al₂O₃ in a laboratory electric furnace, the burnability of the clinker was evaluated through XRD Rietveld analysis and polarization microscopy, and clinker hydration reactivity was reviewed through the Isothermal conduction calorimetry analysis and the cement compressive strength. As a result, the kiln burning temperature for the production of high Al₂O₃ content clinker lower, and the compressive strength was equal to or higher than OPC. Therefore it was confirmed the possibility to manufacturing energy-saving high Al₂O₃ content clinker using a large amount of industrial by-products.

• Journal of the Korea Institute of Building Construction
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• v.13 no.4
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• pp.391-399
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• 2013

For high strength concrete of 40~60 MPa, the effects on the early strength and concrete dry shrinkage properties replacing 60~80% of Ordinary Portland Cement with Blast Furnace Slag Powder and using the Alkali Activator (Modified Alkali Sulfate type) are considered in this study. 1% Alkali Activator to the binder, cumulative heat of hydration for 72 hours was increased approximately 45%, indicating that heat of hydration contributes to the early strength of concrete, and the slump flow of concrete decreased slightly by 3.7~6.6%, and the 3- and 7- strength was increased by 8~12%, which that the Alkali Activator (Modified Alkali Sulfate type) is effective for ensuring the early strength when manufacturing High Strength Concrete (60%) of Blast Furnace Slag Powder. Furthermore, the dry shrinkage test, both 40 MPa and 60 MPa specimens had level of length changes in order of BS40 > BS60 > BS60A > BS80A, and the use of the Alkali Activator somewhat improved resistance to dry shrinkage.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.4
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• pp.324-331
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• 2023

In this study, the hydration and carbonation properties of circulating fluidized bed boiler (CFBC) ash with different free-CaO contents were investigated. In addition, the possibility of utilizing CFBC ash with a high free-CaO content as a cementitious material was investigated by carbonation curing as a pretreatment. The CFBC ash with high free-CaO content exhibited rapid setting behavior and low early compressive strength when mixed with cement. For CFBC ash with high free-CaO content, carbon dioxide capture increased with the duration of carbonization curing. In addition, the free-CaO value decreased together, indicating that the free-CaO reacted with carbon dioxide. When the CFBC ash with high free-CaO content was pretreated by carbonation, no fresh set appeared, and the initial compressive strength was improved. From the results of this study, it is confirmed that CFBC ash with high free-CaO content has a high potential to be utilized as a cementitious material through proper carbonation curing.

• Journal of the Korean Ceramic Society
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• v.39 no.7
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• pp.680-686
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• 2002

The solidification/stabilization mechanism of each cementious material was investigated. It was found that when $C_3$S was hydrated , the Pb element could be transferred to the insoluble Ca[Pb(OH)$_3$.$H_2O$]$_2$and the Cr element to the CaCr $O_4$$H_2O$. The addition of heavy metal tends to delay the hydration until initial 7 days. The Pb element as also delayed the hydration and the Cr element was substituted for the ettringite. On the occasion of the hydration of $C_4$ $A_3$ $S^{S}$, the Pb and Cr ions were solidified/stabilized by the substitution into the ettringite and/or monosulfate. Leaching of the Pb, Cr and Zn elements in the solidified material was extremely little, indicating that heavy metals were effectively solidified/stabilized in the hydrated cementious materials. Solidification/stabilization of heavy metal ions in the industrial wastes such as the STS, BF and COREX sludge was investigated. In case of the mixing ratio of cement and slag was 3 : 7, leaching of hazardous heavy metal ions was very little, indications that the solidification and stabilization was very successful.l.

• Magazine of the Korea Concrete Institute
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• v.6 no.5
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• pp.131-139
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• 1994

The min aim of thls study was to evaluate the effect of particle slze of the fly ash as a cement additive. Experimental work was carried out with three different sizes of fly ash. 18.58, 8.95 and 4.02{$mu}m$ in average radius. Namely, the effect of particle size variation of fly ash on the physical properties of cement paste was investigated. The jluidity was decreased with increasing the addition of fly ash to cement paste regardless of the particle size variation. The decrement of the fluidity of the pulverized fly ash was higher than that of the spherical fly ash. On the other hand, the pozzolan reactivity increased with lowering particle size. In the case of specimens with 5% up to 10% addition of fly ash having a particle size of 4.02{$mu}m$. the compressive strength was increased as compared with the plain specimens before curing for 28 days and showed higher value above 800kg /$cm^2$ when cured for 60 days.This increased compressive strength was ascribed to both the closer packlng of fine particles and the pozzolan reactivity of fly ash. These results were comfirmed by measuring both the porosity of the specimens and Ca(OH ), contents remained in specimens. This work showed that could be effectively ut~lized as a blending material without any de crease in the strength of early hydration stage if we can control the particle size of fly ashes by sizing or pulverizing.