• Journal of Environmental Health Sciences
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• v.34 no.1
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• pp.108-115
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• 2008

This study was performed to investigate the current status, in Korea, of the production of asbestos containing products (ACPs) such as asbestos cement products, asbestos friction materials, asbestos joint sheets, asbestos textile products, and other asbestos-containing products from May 2 to July 30, 2007. The information on ACPs was obtained through written questionnaires from 16 of the 27 companies that produce ACPs in Korea. The production amounts of asbestos containing gaskets were 70 tons in 2004, 90 tons in 2005, and 55 tons in 2006 in 4 companies and that of asbestos friction materials were 435.5 tons in 2004, 540.4 tons in 2005, and 454.3s ton in 2006 in 10 companies. The type and number of ACPs were:- 19 asbestos cement products, produced by 2 companies; 47 asbestos friction materials produced by 18 companies; 12 asbestos joint sheets productes by 4 companies; 18 asbestos textile products from 3 companies, and 6 other asbestos products from 5 companies. The database of ACPs was constructed to include the products name, identification number, name of company, production year, composition, asbestos content (%), usage, specification, and a picture. The database will be used to efficiently identify ACPs and to avoid asbestos exposure in workers and the general population.

• Advances in concrete construction
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• v.13 no.5
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• pp.349-360
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• 2022

The rising prices of landfills and the lack of cement production are motivating researchers to be more interested in using wastes to produce concrete mixtures materials. The use of waste materials such as eggshell and matakoline waste not only reduces landfill costs and space, but also reduces the cost of cement production for the concrete mixture. However, recycling waste materials has become critical in order to effectively manage environmental sustainability. The purpose of this paper is to investigate the appropriate properties of self-compacting concrete (SCC) by incorporating waste materials such as crushed ceramics as coarse aggregate and nano egg shell (NES) and nanoclay (NC) as cement replacements. Fresh properties of SCC, such as segregation, flow time and diameter, V-funnel, H2/H1 ratio, and fresh unit weight of concrete mixtures, as well as hardened properties, such as 7, 14, and 28 days compressive strength and 28 and 90 days flexural strength, were measured for this purpose. The presence of NC in the SCC mixture enhanced the compressive strength of the concrete when 5% of NES was added or in the case without the addition of NES compared to the control mixture. The flexural strength enhanced with the incorporation of NC in the SCC increased the flexural strength of the concrete compared to the control mixture, but the incorporation of 5% of NES decreased the flexural strength compared to the mixtures with NC. These results prove the possibility of using crushed ceramics as the coarse aggregate, and NES and NC as substitutes for 5, 7, and 10% of the cement in SCC, because the properties of such SCC in hardened and fresh states are satisfactory.

• Restorative Dentistry and Endodontics
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• v.47 no.3
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• pp.31.1-31.9
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• 2022

Objectives: This study aimed to evaluate in vitro the effects of the self-adhesive resin cements RelyX U200 (3M ESPE) and seT PP (SDI Limited) on murine macrophages and the interference of the photoactivation. Materials and Methods: Cell viability assays, cell adherence, yeast phagocytosis of Saccharomyces boulardii and production of reactive oxygen species (ROS) were performed in the presence of capillaries containing the respective self-adhesive cement when photoactivated or not. Results: After long periods of contact, both types of cements, when not photoactivated, are more cytotoxic for macrophages. The seT PP cement when only chemically activated seems to interfere more negatively in the process of phagocytosis of yeasts S. boulardii. Both types of cements interfere in the cell adhesion process, independent of photoactivation. None of the types of cements tested was able to induce the production of ROS. Conclusions: Our results highlight the great importance of the photoactivation of self-adhesive resin cements in the dental clinic, since RelyX U200, when photoactivated, presented the best results within the evaluated parameters.

• Journal of the Korean Ceramic Society
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• v.35 no.5
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• pp.479-485
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• 1998

Raw mateials such as limestone quartzite bauxite and anhydrite were used in the production of mod-ified beloite cement. Two kinds of clinker were synthesized with relatively higher content of $C_2S$ than that of $C_4A_3{\={S}}$ Concerning $C_2S$ the main mineral component borax ($Na_2O\;2B_2O_3\;10H_2O$) was added to stimu-late hydraulic reactivity and this would be possible by stabilizing ${\alpha}'-C_2S$ at room temperature. We had in-tended to compare burning and hydraulic characteristics of clinkers with one another by varying the amount of borax addition and to study the appropriate amount of anhydrite addition needed in the strengthening of cement during hydration. It was concluded that the effective amount of borax addition ne-eded for stabilization of ${\alpha}'-C_2S$ was 5 wt% in 60wt% $C_2S$ inclusive clinker and adding anhydrite in the ra-tio of 1.3 of $SO_3/Al_3O_3$ was appropriate in the production of cement by this clinker. Only ettringite was seen to contribute to the strength without additives but C-S-H was found to form along with ettringite with the addition of borax in the initial stage of hydration.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.539-544
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• 2002

The properties of mortar and concrete including metakaolin as a partial cement replacement were investigated in terms of fluidity and compressive strength. The results show that mortar and concrete in which 10 % of cement is replaced with metakaolin exhibit much higher compressive strength after 3 days of hydration than ordinary Portland cement, indicating that metakaolin can be used in the production of high strength concrete replacing silica fume. The type of superplasticizer largely affected on the fluidity and compressive strength of mortar and concrete including metakaolin. It was concluded that when metakaolin is used for the purpose of manufacturing high strength concrete, it is desirable to use PNS based blends rather than PNS, PMS and polycarboxylate based superplasticizer.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.228-231
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• 2004

The purpose of this study evaluates possibilities of waste phosphogypsum into concrete by steam curing admixture. The waste phosphogypsums were classified into 4 forms(Dihydrate, $\beta-Hemihydrate$, III-Anhydrite and II-Anhydrite) which were changed to in low temperature of calcination. Also, various admixtures were made of waste phosphogypsum(PG) and pozollanic fine powderers (Fly-ash, Blast Furnace Slag), and the basic properties of the cement mortars incorporating with these admixtures were examined and analyzed under a verity of experimental conditions. As a result, III-Anhydrite, these is similar to II-Anhydrite from compressive strength and are great in the effect of strength improvement. also, it was proved that specimens made on type III-Anhydrite of waste phosphogypsum and blast furnace slag increased on the compressive strength of cement mortar. Therefore, III-Anhydrite phosphogypsum calcined at lower temperature could be used as steam curing admixture for concrete 2th production.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2018.05a
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• pp.189-190
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• 2018

This study produced Portland limestone cement at the rate of limestone substitution by grinding limestone and clinker together, and it conducted an XRD analysis to determine the sign language response structure as a basic study on Portland Limestone Cement. As a result of the XRD analysis, the higher the substitution rate of limestone, the more likely it is that the detection rate of ettringite is decreased. Additionally, we could see that the production volume of Mono-carbonate was increasing.

• Proceedings of the Korea Concrete Institute Conference
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• 1996.10a
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• pp.154-165
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• 1996

As II-anhydrite reacts with C3A(aluminate), C4AF(ferrite) at initial hydration of cement and assists the hydrolysis of C3S(calcium silicate), the production rate of ettringite(3C3A.3CaSO4.32H2O) and C-S-H gel was acclerated. It was known that compressive strength of cement concrete improved due to the effect of II-anhydrite. For the checking these effects of II-anhydrite, the fluidity and compressive strength of cementmortar admixed with II-anhydrite and pozollanic fine powders were investigated. By means of SEM analysis, the surface structure of mortar with the condition of steam curing at curing days=28 was investigated. As a result of this experiment, it was examined that II-anhydrite had an increase on the fluidity of cementpaste and compressive strength of mortar.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2018.11a
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• pp.116-117
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• 2018

The aim of this study is to investigate the properties of hardened mortar with chlorine by-pass system(CBS) in cement production in blast furnace slag(BS) mixed cement. Compressive strength had a tendency to be increased when the CBS Dust was replaced by 10% at the BS replacement rate of 0%. The 65% combination of BS showed a tendency to decrease as the CBS Dust exchange rate increases. Flexural strength was reduced as CBS Dust exchange rate increases in BS replacement ratio of 0%. The use of 5% of CBS dust can contribute to enhance the quality of non reinforced concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.801-804
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• 2006

Polycarboxylate type superplasticizers(PC) have got widely used for making not only high performance concrete but low grade concrete as well. It is known that fluidity of cement with PC is affected by the characteristics of cement especially sulphate ion concentration and hydration activity. But the characteristics of PC also affect the fluidity. The fluidity of cement mortar with various types of PC was measured and critical dosage(CD) and dispersing ability(DA) was calculated. CD and DA is strongly dependent on the type of PC. And the variation of fluidity on time was affected by the type of PC also. So, it is advisable to investigate the property of PC before production of concrete and adjust it to meet the requirements of concrete depending on the materials, the time of transport and so on.