• Title/Summary/Keyword: gypsum content

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Influence of the Kinds and the Content of Expansive Additive on the Properties of Shrinkage of High Performance Concrete (고성능 콘크리트의 수축특성에 미치는 팽창재 종류 및 혼입률의 영향)

  • 배정렬;홍상희;고경택;김성욱;한천구
    • Proceedings of the Korea Concrete Institute Conference
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    • 2003.05a
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    • pp.349-354
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    • 2003
  • The objective of this paper is to investigate the length change of high performance concrete using expansive additives to reduce autogenous shrinkage and drying shrinkage. The kinds and the contents of expansive additives are varied. The expansive additives are used made from Japan(CSA type;JEA), China(CSA type;CEA) and Korea(gypsum type; KEA), respectively. According to results, remarkable variations of the properties at fresh concrete are not found with dosage of expansive additives. For compressive strength, it decreases about 6-10% with expansive additives of 10%. Autogenous shrinkage decreases about 32%, and drying shrinkage does about 35%, respectively, with expansive additives of 5%, and about 68% and about 55%, with expansive additives of 10%. Accordingly, expansive additives demand requires 10% by cement weight in order to reduce shrinkage of high performance concrete more effectively in the sphere of this study, and JEA shows the best shrinkage reducing performance among the tested expansive additives.

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The Effect of Seawater on the Hydration of Clinker Minerals (II) Acceleration Experiment in the Artificial Seawater (시멘트 클린커광물의 수화에 미치는 해수성분의 영향 (II) 인공해수에서의 촉진시험)

  • 신도철;송태웅;최상흘;한기성
    • Journal of the Korean Ceramic Society
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    • v.25 no.1
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    • pp.15-20
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    • 1988
  • In this study, the specimens of cement clinker minerals such as 80C3-S-15C4AF-5C3A added various blending materials were immersed in artificial seawater. In order to ascertain the effect of SO3 and blending materials on seawater resistance of the specimens, the acceleration experiment in the artificial seawater was carried out by repeating of immersion and drying operation periodically. As inner part of the specimen immersed in artificial seawater, Friedel's salt was produced by reaction with Cl ion. In outer part of the specimen, gypsum and ettringite were mainly formed. With the increase of SO3 content in the specimen the formation of ettringite was increased and Frieldel's salt in inner part was decreased. Total pore volume of the specimens was increased according to the amount of Cl ion penetrated and Mg(OH)2 leached in the solution.

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Foamed Concrete with a New Mixture Proportioning Method Comparable to the Quality of Conventional ALC Block (ALC 블록성능의 기포콘크리트 배합설계 연구)

  • Yang, Keun-Hyeok
    • Journal of the Korea Institute of Building Construction
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    • v.15 no.1
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    • pp.1-7
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    • 2015
  • The objective of this study is to develop a high-performance foamed concrete made with a new mixture proportioning as an alternative of autoclaved lightweight concrete (ALC) block. For the early-strength gain of the foamed concrete under an atmospheric curing condition, the binders and chemical agents were specially contrived as follows: 3% anhydrous gypsum was added to ordinary portland cement (OPC) in which $3CaO{\cdot}SiO_2$ content was controlled to be above 60%; and the content of polyethylene glycol alkylether in a polycarboxylate-based water-reducing agent was modified to be 28%. Using these binders and chemical agents, 11 mixes were prepared with the parameters of W/B ratio (30% to 20% in a interval of 2.5%) and unit binder content ($400kg/m^3$ to $650kg/m^3$ in a interval of $50kg/m^3$). The quality and availability of the mixed foamed concrete were examined according to the minimum requirements specified in the KS for ALC block and existed conventional foamed concrete. The measured properties satisfied the minimum requirement of KS for ALC block and proved that the developed high-performance foamed concrete had considerable potential for practical application.

THE LEVEL OF RESIDUAL MONOMER IN INJECTION MOLDED DENTURE BASE MATERIALS

  • Lee Hyeok-Jae;Kim Chang-Whe;Kim Yung-Soo
    • The Journal of Korean Academy of Prosthodontics
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    • v.41 no.3
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    • pp.360-368
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    • 2003
  • Statement of Problem: The residual monomer of denture base materials causes hypersensitivity on oral mucosa and intereferes with the mechanical properties of the cured resin. The amount of residual monomer is influenced by materials, curing cycle, processing method, and etc. Purpose: The aim of this study was to investigate the residual methyl methacrylate(MMA) content of injection molded denture base polymer, and to compare this with the self-cured resin and the conventional compression molded heat-cured resin. Materials and Methods: Disc shaped test specimens (50mm in diameter and 3mm thick) were prepared in a conventional flasking technique with gypsum molding. One autopolymerized denture base resins (Vertex Sc. Dentimex. Netherlands) and two heat-cured denture base resins (Vertex RS. Dentimex. Netherlands, Ivocap. Ivoclar Vivadent, USA) were used. The three types of specimens were processed according to the manufacturer's instruction. After polymerization, all specimens were stored in the dark at room temperature for 7 days. There were 10 specimens in each of the test groups. 3-mm twist drills were used to obtain the resin samples and 650mg of the drilled sample were collected for each estimation. Gas chromatography (Agillent 6890 Plus Gas Chromatograph, Agillent Co, USA) was used to determine the residual MMA content of 10 test specimens of each three types of polymer. Results: The residual monomer content of injection molded denture base resins was $1.057{\pm}0.141%$. The residual monomer content of injection molded denture base resins was higher than that of compression molded heat cured resin ($0.867{\pm}0.169%$). However, there was no statistical significant difference between two groups (p>0.01). The level of residual monomer in self cured resin($3.675{\pm}0.791$) was higher than those of injection molded and compression molded heat cured resins (p<0.01). Conclusion: With respect to ISO specification pass / fail test (2.2% mass fraction) of residual monomer, injection molding technique($1.057{\pm}0.141%$) is a clinically useful and safe technique in terms of residual monomer.

Effect of Chlorine Content in Clinker on Setting and Compressive Strength of Early Strength Cement (클링커 염소 함량이 조강형 시멘트의 응결 및 압축강도에 미치는 영향)

  • Jae-Won Choi;Byoung-Know You;Dong-Kyun Seo;Kyoung-Seok Kim;Min-Cheol Han
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.11 no.3
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    • pp.218-225
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    • 2023
  • In this study, we examine the feasibility of using chlorine in clinker as an early-strength cement by the effect of accelerating the cement hydration reaction of chlorine. Clinker with a chlorine content of 200-1,000 ppm was prepared using actual cement kilns, and 46 cement samples were prepared by adding gypsum and admixtures(GGBFs and limestone). We measured consistency, setting, 1-28 days compressive strength and analyzed them statistically. Test results indicated that an increase of the chlorine content resulted in shortening of initial and final setting time and the improvement of 1 day compressive strength. But the 28 days compressive strength was decreased. Specifically, when the chlorine content was increased from 230 to 965 ppm, the 1 day compressive strength increased up to 4.6 MPa, improvement effect was superior to that of increasing Blaine in the range of 3,400-3,970 cm2/g.

Investigation on Natural Radioactivity of Environmental Samples Near the Phosphate Rock Processing Facility (인광석 사용업체 주변 환경시료의 자연방사능 조사)

  • Lee, Gill-Jae;Koh, Sang-Mo;Chang, Byung-Uck;Kim, Tong-Kwon;Kim, Young-Ug
    • Economic and Environmental Geology
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    • v.44 no.1
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    • pp.37-48
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    • 2011
  • Some industrial minerals used in domestic industries such as monazite, apatite, bauxite, and ilmenite belong to NORM (Naturally Occurring Radioactive Materials) because they show a high radioactivity. Products, semi-products, wastes, and by-products which show higher radioactivity than NORM belong to TENORM (Technologically Enhanced Naturally Occurring Radioactive Materials). Apatite used for manufacturing phosphate fertilizer in Namhae Chemical company belongs to NORM, and its by-product, phospo-gypsum, belongs to TENORM. A geological investigation is needed for the future environmental impact assessment of the Namhae Chemical company's site. According to survey results of the Namhae Chemical company's site, soil mineral composition indicated the mixture of minerals derived from the country rock (quartz, feldspar, mica, $l4{\AA}$ mineral, kaolin and amphibole) and minerals from the gypsum open-air storage yard (gypsum and apatite). Soil samples showed average content of U 4.6 ppm and Th 10 ppm, which are similar to average crustal abundances. They also show average contents of $^{40}K$ 191-1,166 Bq/kg, $^{226}Ra$ 15.6-710 Bq/kg, and $^{232}Th$ 17.4-72.7 Bq/kg, which indicate moderate levels of radio nuclide. But $^{226}Ra$ anomaly in the gypsum open storage yard is clearly confirmed and $^{232}Th$ anomaly is also confirmed in the east road side of the factory and nearby mountain areas. Soil external hazard indices ranged 0.24-2.01 with the average 0.54. Although most external hazard indices were lower than 1, which means radiation hazard index to be negligible, 5 samples out of total 40 samples showed higher values than 1, and further detailed investigation is needed.

Estimation of soil Quantity and Environmental Effect on Dredged Soil (준설오니의 토량 산출 및 성분분석)

  • 신은철;오영인
    • Journal of Korea Soil Environment Society
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    • v.5 no.2
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    • pp.13-21
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    • 2000
  • Detention basin is the temporary holding pond of treated water prior to flow out to the sea. It is very common to dredge the soil from the bottom of detention basin to keep up the water holding capacity. In this study, the amount of volume reduction of dredged soil from detention basin was estimated based on the laboratory test results. The percentage of soil particles in dredged organic soil is about 12.5∼21.9% by weight. The content of heavy metal and environmental effect for dredged soil itself and solidified dredged soil were analysed and the results are meet the standards of environmental requirement.

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A Study on the Automatic Irrigation Control System in the Vinyl-House Cultivation Utilizing Microcomputer (마이크로컴퓨터를 이용한 시설원예작물 재배의 관개자동화에 관한 연구)

  • Kim, C.S.;Kim, J.H.;Chung, S.W.
    • Journal of Biosystems Engineering
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    • v.14 no.2
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    • pp.128-136
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    • 1989
  • The purpose of this study was to develop a computer operated automatic drip irrigation system for application in vinyl-house cultivation. The results can be summarized as follows: 1) The T-type ice compensation wire was used to measure the temperature. The voltage level measured up to 0.02 volt was used as input to an 8-bit A/D converter. 2) A specially devised tensiometer was used to content the watering system. When the needle of the pressure gauge reaches the lower threshold position it turns on the pumping system and turns off when it reaches higher threshold position. 3) In order to use the multiple gypsum blocks for one transducer, reed relays and a D/O board were used to make the sequential switching possible. 4) It was possible to automate the trickle irrigation system for the whole growth period of vinyl-house crops with the help of microcomputer. 5) In terms of furrow irrigation, the irrigation water consumption was the smallest, 2.8 times less than conventional method of surface trickle irrigation, 3.4 times less than subsurface trickle irrigation method. 6) In terms of productivity of cucumber, there was a drop in productivity when compared to furrow irrigation method, 7.2% for surface trickle irrigation, 27.4% for subsurface irrigation method.

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Trends of phosphorus recovery technology from sewage sludge ash by wet chemical method (습식 화학적 방법에 의한 하수 슬러지 소각재에서의 인 회수 기술동향)

  • Lee, Min-Su;Kim, Dong-Jin
    • Journal of Korean Society of Water and Wastewater
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    • v.32 no.2
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    • pp.131-143
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    • 2018
  • Phosphorus (P) is a limited, essential, and irreplaceable nutrient for the biological activity of all the living organisms. Sewage sludge ash (SSA) is one of the most important secondary P resources due to its high P content. The SSA has been intensively investigated to recover P by wet chemicals (acid or alkali). Even though $H_2SO_4$ was mainly used to extract P because of its low cost and accessibility, the formation of $CaSO_4$ (gypsum) hinders its use. Heavy metals in the SSA also cause a significant problem in P recovery since fertilizer needs to meet government standards for human health. Therefore, P recovery process with selective heavy metal removal needs to be developed. In this paper some of the most advanced P recovery processes have been introduced and discussed their technical characteristics. The results showed that further research is needed to identify the chemical mechanisms of P transformation in the recovery process and to increase P recovery efficiency and the yields.

An Aspect of Weathering Progress Based on Physical and Chemical Properties of Tafoni in the Simgok Area of Gangneung, Korea (강릉 심곡 해안에 발달한 타포니의 물리·화학적 특성에 기초한 풍화 진행 양상)

  • Kim, Yu Jung;Kim, Jong Yeon;Kim, Jong Wook;Han, Min
    • Journal of The Geomorphological Association of Korea
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    • v.25 no.3
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    • pp.19-42
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    • 2018
  • In this study, we surveyed weathering progressing aspect by major elements variation and rock hardness by using XRF analysis, schmidt hammer, and thin section analysis. This observation suggested that the weathering process is likely to develop differently according to microstructural characteristics. R-value on the inside wall are lower than those on the outside. Also, the shadier the environment was, the closer it was to inshore areas, the R-value appeared to be lower. The movement of the elements such as Ca, Na and K shows that feldspar is hydrolyzed and can form salt crystallization like a gypsum or halite when they combine with the elements such as S or Cl. It proved a high CaO, $Na_2O$ and $K_2O$ content on flaking inside wall and rock meal. The exfoliation was mainly observed along the shady backwall and ceiling of tafoni. This helped in predicting the growth of tafoni as well as the direction of its progress.