• Proceedings of the Korea Concrete Institute Conference
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• 1997.10a
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• pp.229-234
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• 1997

The objective of this study is to develop the non crack ready mixed concrete and the high quality concrete under various addition ratios of expansive additives. According to the experiment results, when expansive additive are mixed in concrete mixture by about 6% per cement contents, in W/B of 45~55%, it is found that the strength increase and the shrinkage compensation can be achieved by about 2~3 times. And it is considered to produce high quality concrete and non crack ready mixed concrete.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.11a
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• pp.127-128
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• 2022

In order to realize carbon neutrality in the international society, research on supplementary cementitious materials(SCMs) has been actively conducted as a way to reduce carbon dioxide emissions in the cement industry. However, the use of SCMs causes problems of initial hydration delay and strength reduction due to the reduction of tricalcium silicate(C3S) in the cement clinker. Therefore, in this study, the initial hydration and basic characteristics of cement mortar were confirmed by adding a C-S-H based hardening acceleration to blended cement mixed with Portland cement, blast furnace slag, fly ash, and limestone power. As a result of the heat of hydration and compressive strength test, it was confirmed that when hardening acceleration was added, the initial reactivity was high, so the heat of hydration was promoted, and the initial strength was increased. It is considered to be due to C-S-H seeding effect. Therefore, it is judged that the use of C-S-H based hardening acceleration can supplement the problem of initial hydration delay of blended cement in Korea.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.05a
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• pp.115-116
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• 2023

This study aims to investigate and improve the carbon dioxide sequestration capability and the mechanical properties of non-hydraulic low calcium silicate cement especially designed for CO₂ reaction and ordinary Portland cement subjected to the carbonation curing facilitating pH swing method. Nitric acid (HNO₃) was utilized as an liquid for the mixing of cement paste to enhance the initial dissolution of Ca ions from the cements by promoting low pH environment and prevent the direct precipitation of Ca with the anion, owing to the high solubility of Ca(NO₃)₂ in water. The results presented that the higher the concentration of HNO₃, the higher the compressive strength and CO₂ sequestration (until 0.1 M). Ca dissolution caused by the harsh acid attack onto the anhydrous cement particle lead to the higher carbonation reaction degree, forming abundant CaCO₃ crystals after the reaction. However, cement paste mixed with excessively high concentration of HNO₃ presented deterioration due to the too harsh pH environment and abundant NO₃- ions which are known to retard the reaction of cement.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.6C
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• pp.259-265
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• 2012

This paper investigates engineering characteristics of lightweight soils mixed with air foam and tire powder. Lightweight soils could be used as foundation materials, back-fills of reducing vibrating or abutment, and so on. Unconfined and triaxial compression tests were carried out to analyze strength and deformation characteristics of lightweight soils by changing target moist unit weight and cement contents. In comparison with strength characteristics of two different kinds of lightweight soils with same most unit weights ($13kN/m^3$), unconfined compression tests showed similar compressive strength, however, triaxial compression tests showed that compressive strength of lightweight soils mixed with waste tire powder was relatively larger strength than that of lightweight soils mixed with air foam because of elasticity of waste tire powder. Also, unconfined and triaxial compressive strengths of most of lightweight soils increase with increases of moist unit weight and cement contents. However, the strength of lightweight soils mixed with air foam under $11kN/m^3$, when moist unit weight exceeds a certain cement contents, decreases even though cement contents increase because of the effect in a void gap of air foam.

• Journal of The Korean Society of Agricultural Engineers
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• v.54 no.6
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• pp.159-167
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• 2012

In the present study, an investigation has been made on the application of cement-bentonite soil mixtures as the countermeasure against leachate produced by buried animal carcasses. For this purpose, the strength characteristics of the cement-bentonite soil mixtures mixed with geotextile and metakaolin. After the mixtures with different contents of the cement (0 %, 10 %), bentonite (0 %, 5 %, 10 %, 15 %, 20 %), and weathered soil (100 %, 95 %, 90 %, 85 %, 80 %) were prepared, metakaolin and geotextile were added with different contents (metakaolin : 0 %, 5 %, 10 %, 15 %, 20 % of the cement weight; geotextile : 0 %, 0.5 %, 1 %, 1.5 %, 2 %). Experimental results suggested that the early strength of the mixture increases due to the pore filling, the hydration acceleration, and the pozzolan reaction when metakaolin of 5~10 % of the cement weight was added. In addition, the compressive strength increase when 0.5~1 % geotextile contents were added, and the above these contents, the rate of strength increase was gradually decreased because of the fibrous tangles.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.3
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• pp.89-96
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• 2013

Now-a-days, a manhole adopted since the late 1990s and produced using the polymer concrete has widely used due to the various benefits. While entering the High oil prices times, however, and with the price increase of the petrochemical materials, the cost of manufacture of polymer concrete was elevated and the resulting polymer concrete's weakness is being put on. Accordingly, the development of economic cement concrete manholes, which can replace the outstanding bending strength of manhole made of high-price polymer concrete, has been required. In this study, based on the cement technology of fast hardening armorphous calcium aluminate (ACA), by minimizing the amount of cement using the industrial byproducts, to develop the eco-friendly high-toughness concrete manhole, which can reduce $CO_2$ reduction, was intended. As the results, the cement concrete manhole, which economic, eco-friend, and meeting the performance requirements, was developed.

• Magazine of the Korea Concrete Institute
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• v.7 no.3
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• pp.156-163
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• 1995

In the previous study, styrene mdleic dnhydride copolymer(SMA) as synthesized flom styrene and rnale~c dnhydr~de and further redcted with sulfuric acid to obtam water soluble SMA. In thls study, the flow dnd strcngth tests of cement mortar rmxed wth copolymers wele carried out to evaluate the capability of copolymers as high range water reducer for the con crete. It was found from flow exper~ment that the fluidity of cenient mortar rmxed wth sulfonated SMA(SSMAj was larger thdn that mxed ulth amnophenol substituted SSMA (SmSMAj. The decreasing rate of the flow of cement mortar rmxed ulth SSMA and SmSMA was significantly lower than that mixed ulth naphthalene condensate(NSC) The compressslve strength of the hardened cement mortars containing 0.5% copolymers after 28 dys curing was exarmned. 'The compressive strength of hdrdened cement mortar containing SSMA and SmSMA was mcreased up to 31% and 13%, respectively, when omp pared to the plain. As the results, the copolyniers(SSMA and SrnSMA) used in thls study are greatly expected as a good high range water reducers for the concrete.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.3
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• pp.247-252
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• 2017

The aim of this research is the feasibility analysis of the reject ash premixed cement mortar with combined aggregate. Namely, for the combined aggregate with two different qualities of aggregates, a fundamental properties of cement mortar was evaluated depending on various replacing ratios of reject ash(Ri). According to the experimental results, the combined aggregate consisted with low-quality aggregate and sea sand did not change the flow value depending on the reject ash while the combined aggregates consisted with low quality aggregate and sea sand; and consisted exploded debris sand and sea sand the increasing reject ash increased the air content with increased replacing ratio of reject ash. In the case of compressive strength, as the replacing ratio of reject ash was increased, the compressive strength was increased. It is considered that when 5% of reject ash replacing ratio made similar quality of cement mortar with favorable quality aggregate, hence, it can be suggested that 5% replacement of reject ash for desirable fluidity and compressive strength of concrete.

• Magazine of the Korea Concrete Institute
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• v.8 no.4
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• pp.161-169
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• 1996

Styrene-maleic anhydride copolymers with different composition (1:1SMA. 5:1SMA) were synthesized and further reacted with sulfuric acid to obtain water soluble copolymers (1:1SSMA, 5:1SSM.4). In the flow experiments of cement mortar mixed with copolymers, 5:1SSMA showed higher fluidity than 1:1SSMA. The cement mortar mixed with 1% 5:1SSMA maintained 95% of original flow after 60 min. On the other hand, the compressive strength of the hardened cement mortars containing 0.5% copolymers after 28 days curing was also examined. The compressive strength of hardened cement mortar containing 5:1SSMA was increased up to 41% compared to the plain while 1:1SSMA was increased up to 29%. As the results, the 5:1SSMA used in this study are greatly expected as a new high range water reducers for the concrete.

• Restorative Dentistry and Endodontics
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• v.19 no.2
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• pp.409-428
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• 1994

Endodontic surgery is performed when conventional endodontic therapy fails or is contraindicated. In such cases, retrograde filling materials including amalgam, composite resin, and various cements have been used. Biocompatibilty and margin sealing ability of retrograde filling materials are important for the long term success of endodontic surgery. In vitro cell culture is frequently used as the method of measuring the biocompatibilty of dental materials. The purpose of this study was to evaluate the cytotoxicity of six kinds of retrograde filling materials including newly developed light curing glass ionomer cements. Each material was mixed according to. the manufacture's instruction and evaluated as : freshly mixed, 24-hour after mixing, and 168-hour after mixing respectively. The elution solution was extracted after 24-hour contact with materials using media. Cytotoxicity was evaluated by direct contact, or elution contact. Test results of radiochromium($^{51}Cr$) release, cell viability using tetrazolium dye (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl dimethyltetrazolium bromide(MTT) test and lactate dehydrogenase(LD) of damaged L929 cells were analyzed. In the $^{51}Cr$ release of direct contact, all experimental retrograde filling materials except amalgam and glass ionomer cement showed increased cytotoxicity compared to control. In the $^{51}Cr$ release of elution solution, the released $^{51}Cr$ was so minimal that it was impossible. to evlauate the cytotoxicity exactly. The elution solutions of glass ionomer cement and IRM showed marked cytotoxicity in MTT test. LD enzyme activity was highest in tests of direct contact with composite, light curing composite, and light curing glass ionomer cement and IRM. Amalgam revealed least cytotoxicity while IRM showed cytotoxicity using all three methods. Composite, light curing composite and light curing glass iomomer cement were cytotoxic in the tests of $^{51}Cr$ release and LD activity. Glass ionomer cement showed cytotoxic effect only in the MTT method. From these results it is suggested that the standardization and optimization of cytotoxicity testing, especially using elution solutions, should be strongly advised.