• Proceedings of the Korean Institute of Building Construction Conference
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• 2016.05a
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• pp.38-39
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• 2016

In this research, the possibility of wasted refractory powder pulverized from refractory block as an expansive admixture and additional alkaline stimulant for class two and three blast furnace slag cements (BSC) was assessed with its high content of free CaO or free MgO. As the replacement ratios of wasted refractory powder and blast furnace slag were increased, flow and air content were decreased, while unit volume weight was increased under same conditions. Compressive strength of mortar was increased with increased replacement ratio of wasted refractory powder, especially, in the case of class three BSC, the highest compressive strength was obtained when wasted refractory powder was replaced 10 %.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.125-128
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• 2005

Coal ash, which is generated as a byproduct at a coal thermal power plant, can be classified into fly ash and bottom ash. Most of fly ash is recycled as an admixture for concrete, while bottom ash is not recycled but dumped into an ash landfill disposal site. So, if a technology for recycling bottom ash efficiently, which is increasingly generated year by year, is not developed, environmental problems will take place as a matter course and further an enormous economical cost will be required for construction of additional ash landfill disposal sites. In this study an optimum mix proportion design and a quality control method for utilizing the reclamation coal ash as an aggregate for secondary concrete products such as an artificial reef was successfully developed.

• Journal of the Korea Institute of Building Construction
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• v.18 no.5
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• pp.403-412
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• 2018

Recently, needs for utilization of recycled aggregate have been increasing. However, its utilization has been limited due to its high alkalinity, which mostly came from the unremoved cement paste particles that were attached at the surface of recycled aggregate. Various efforts has been made to reduce its alkalinity by using $CO_2$, but currently available methods that uses $CO_2$ generate the problem with pH recovery. Considering the fact that supercritical $CO_2$ ($scCO_2$) can provide more rapid carbonation of cement paste than by normal $CO_2$, $scCO_2$ was utilized in this work. The reaction between $scCO_2$ and hydrated cement paste has been systematically evaluated. According to the results, it was found that powder type showed higher carbonation compared to that of cube specimens. It seems the carbonation by $scCO_2$ has occurred only at the surface of the specimen, and therefore still showed some amount of $Ca(OH)_2$ calcium aluminates after reaction with $scCO_2$. With powder type specimen, all $Ca(OH)_2$ was converted into $CaCO_3$. Moreover, additional calcium that came from both calcium aluminate hydrates and calcium silicate hydrates reacted with $scCO_2$ to form $CaCO_3$. After carbonation with $scCO_2$, the powder type specimen did not show pH recovery, but cube specimens did show due to the presence of portlandite.

• Journal of the Korean Geotechnical Society
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• v.33 no.12
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• pp.35-44
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• 2017

A large amount of recycled aggregates was produced and crushed from old buildings and pavements. In this study, when these aggregates are re-used in subbase or subgrade materials in near construction sites, their engineering characteristics caused by crushing are investigated in terms of permeability and shear strength. Three different sizes of aggregates (31.5-45.0 mm, 19.0-31.5 mm, 9.5-19.0 mm) and their mixtures, a total of 7 types of aggregates were used in compaction tests (modified D and B methods). After compaction tests, aggregates were sieved and analyzed with four different breakage factors ($B_{15}$, $C_c$, $B_{10}$, $B_r$). The D compaction method gave 2.0-8.0 times more crushable than B compaction method. The breakage factors for the largest size aggregate was 1.4-3.0 times higher than those of the smallest size aggregate. For aggregates with 5.6-9.5 mm sizes, the samples were prepared with $B_{15}$ of 1, 3, 10, 20, 30, 50, 60, and 70 for permeability and direct shear tests. As $B_{15}$ increased, the hydraulic conductivity decreased up to 1/22 for $B_{15}=50$. As $B_{15}$ increased from 1 to 50, the peak friction angle increased from $46.1^{\circ}$ to $54.5^{\circ}$. On the other hand, the friction angle decreased after $B_{15}=60$.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.3
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• pp.253-259
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• 2021

Plastic wastes generated from household waste are separated by mixed discharge with foreign substances, and recycling is relatively low. In this study, the effect of the ratio and content of mixed plastic waste coarse aggregate(MPWCA)s and mixed plastic waste fine aggregate(MPWFA)s filled with blast furnace slag fine powder on the slump and compressive strength of concrete was evaluated experimentally. The MPWCAs were found to have a similar fineness modulus, but have a single particle size distribution with a smaller particle size compared to coarse aggregates. However, the MPWFAs were found to have a single particle size distribution with a larger fineness modulus and particle size compared to fine aggregates. Meanwhile, the effect of improving the density and filling pores by the blast furnace slag fine power was found to be greater in the MPWFA compared to the MPWCA. As the amount of the mixed plastic waste aggregate(MPWA)s increased, the slump and compressive strength of concrete decreased. In particular, the lower the slump and compressive strength of concrete was found to decrease the greater the amount of MPWFA than MPWCA when the amount of MPWA was the same. This is because of the entrapped air and voids formed under the angular- and ROD-shaped aggregates among the MPWFAs. On the other hand, the addition of the admixture and the increase in the unit amount of cement were found to be effective in improving the compressive strength of the concrete with MPWAs.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.4
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• pp.514-520
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• 2021

In this study, EMP shielding performance was evaluated using electric furnace oxidized slag to give EMP shielding performance to concrete among the most used materials in construction sites. As a result of the evaluation, the component of the electric furnace oxidation slag was found to have an Fe₂O₃ content of 34%, and it was also found to contain an MgO component of about 4.8%. In addition, as a result of conducting an aggregate stability evaluation due to concerns about expansion due to MgO components, it is considered to be suitable for the KS standard. EMP shielding performance evaluation result showed that there was no correlation in EMP shielding performance according to compressive strength, and that general aggregates did not have EMP shielding. However, it was found that the aggregate using the furnace oxidized slag had excellent EMP shielding performance, and the shielding performance improved as the thickness increased. As a result of the durability evaluation, it was found that the EMP shielding concrete has the durability of abortion compared to the general concrete. Through this, it is thought that it will be good to improve the shielding rate if concrete is manufactured using electric furnace oxide slag when constructing EMP shielding structures in the future.

• Journal of the Korean Geotechnical Society
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• v.40 no.1
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• pp.29-37
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• 2024

In this study, recycled concrete aggregates (RCA) were treated in a 5-kg-scale prototype reactor with carbon dioxide (CO₂) to enhance their material quality and geotechnical performance. The aggregate crushing value (ACV) and California bearing ratio (CBR) were measured on untreated RCAs and CO₂-treated RCAs. After CO₂ treatment, the ACV decreased from 35.6% to 33.2%, and the CBR increased from 97.5% to 102.4%. The CO₂ treatment caused a reduction of fine particle generation and an increase in bearing capacity through carbonation. When CO₂ treatment was performed with mechanical agitation, which provided additional enhancement in mechanical quality, the ACV was reduced further to 30.3%, and the CBR increased to 137.7%. If upscaled effectively, the proposed CO₂ treatment technique would be an effective method to reduce carbon emissions in construction industries.

• Structural Engineering and Mechanics
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• v.62 no.3
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• pp.357-364
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• 2017

This paper presents the results of a study that investigated the improvement of the mechanical properties of coarse and fine recycled asphalt pavement (RAP) produced by adding silica fume (SF) with contents of 5%, 10%, and 15% by total weight of the cement. The coarse and fine natural aggregate (NA) were replaced by RAP with replacement ratio of 20%, 40% and 60% by the total weight of NA. In addition, SF was added to NA concrete mixes as a control for comparison. Twenty eight mixes were produced and tested for compressive, splitting tensile and flexural strength at the age of 28 days. The results show that the mechanical properties decrease with as the content of RAP increases. And the decrease in the compressive strength was more in the fine RAP mixes compared to the coarse RAP mixes, while the decrease in the splitting tensile and flexural strength was almost the same in both mixes. Furthermore, using SF enhances the mechanical properties of RAP mixes where the optimum content of SF was found to be 10%, and the mechanical properties enhancement of coarse RAP were better than fine RAP mixes. Accordingly, the RAP has the potential to be used in the concrete pavements or in other low strength construction applications in order to reduce the negative impact of RAP on the environment and human health.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2005.10a
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• pp.128-134
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• 2005

This study was performed to evaluate the strength and durability properties of recycled concrete containing water - redispersible copolymer powder(WRP) and blast furnace slag powder(BSP) [RCWS]. Material used were cemente, recycled coarse aggregare, natural fine aggregate, water-redispersible copolymer powder, blast-furnace slag powder. Especially, Water-redispersible powder was used for blending with Inorganic binders such as cemente, gypsum and hydrated lime etc. First of all, Mixed ratio method of RCWS made Two Type. One was called type-1 which used to BSP content 5% and WRP(Water-redispersible powder) content 0%, 1%, 2%, 3%, 4%, 5%, 6%. respectively. Another was called Type-2 which used to BSP(blast furnace slag powder)content 10% and WRP(Water-redispersible powder) content 0%, 1%, 2%, 3%, 4%, 5%, 6%. respectively. According to the experimental results of (RCWS), Incase Type-2 at curing age 28days, Compressive strength, pulse velocity and dynamic modulous of elasticity were shown higher than Type-1 and The more WRP content increasing($0%{\sim}6%$) was the lower Compressive strength, Pulse velocity and Dynamic modulous of elasticity. Water absorption ratio was in the range of $3.85%\;{\sim}\;3.23%$, it was almost equal to Type-1, 2 but Increasing the WRP content($0%{\sim}6%$), The water absorption ratio is decreased.

• Journal of the Korea Institute of Building Construction
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• v.13 no.1
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• pp.29-37
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• 2013

In this study, a zero-cement brick is manufactured by replacing cement with recycled aggregates and blast furnace slag powder. Experimental tests were conducted with standard sized samples of $190{\times}57{\times}90mm$ (KS F 4004), and this manufacturing technique was simulated in practice. Results showed that the zero-cement brick with 0.35 W/B had the highest compressive strength, but the lowest absorption ratio. This absorption ratio of zero-cement brick with 0.35 W/B was lower than the required level determined by KS F 4004. Hence, to increase the absorption ratio, crushed fine aggregate (CA) and emulsified waste vegetable oil (EWO) were used in combination in the zero-cement brick. It was found that the zero-cement brick with CA of 20% and EWO of 1% had the optimum combination, in terms of having the optimum strength development (12 MPa) and the optimum absorption ratio (8.4%) that satisfies the level required by KS. In addition, it is demonstrated that for the manufacturing of zero-cement brick of 1000, this technique reduces the manufacturing cost by 5% compared with conventional cement brick.