• Title/Summary/Keyword: calcium silicate cement

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Conceptual Geochemical Modelling of Long-term Hyperalkaline Groundwater and Rock Interaction (지구화학 모델을 이용한 장기간의 강알칼리성 지하수-암석의 반응 개념 모델링)

  • Choi, Byoung-Young;Yoo, Si-Won;Chang, Kwang-Soo;Kim, Geon-Young;Koh, Yong-Kwon;Choi, Jong-Won
    • Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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    • v.5 no.4
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    • pp.273-281
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    • 2007
  • Hyperalkaline groundwater formed by groundwater-cement components and its reaction with bedrock in a nuclear waste repository were simulated by geochemical modeling. The result of groundwater-cement components reaction showed that the pH of water was 13.3 and the precipitated minerals were Brucite, Katoite, Calcium Silicate Hydrate(CSH1.1), Ettringite, Hematite, and Portlandite. The result of interaction between such minerals and groundwater sampled in Gyeongju area also showed that the pH of groundwater reached 12.4. Interaction between such hyperalkaline groundwater and granite was simulated by kinetic model during $10^3$ years. This result showed that the final pH of groundwater reached 11.2 and the variation of pH was controlled by dissolution/precipitation of silicate and CSH minerals. Groundwater quality was also determined by dissolution/precipitation of silicate, CSH, oxide minerals. Our results show that geochemical modeling of long-term hyperalkaline groundwater and rock interaction can contribute to the safety assessment of engineered barrier by predicting geochemical condition in repository site.

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Effects of the exposure site on histological pulpal responses after direct capping with 2 calcium-silicate based cements in a rat model

  • Trongkij, Panruethai;Sutimuntanakul, Supachai;Lapthanasupkul, Puangwan;Chaimanakarn, Chitpol;Wong, Rebecca;Banomyong, Danuchit
    • Restorative Dentistry and Endodontics
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    • v.43 no.4
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    • pp.36.1-36.12
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    • 2018
  • Objectives: Direct pulp capping is a treatment for mechanically exposed pulp in which a biocompatible capping material is used to preserve pulpal vitality. Biocompatibility tests in animal studies have used a variety of experimental protocols, particularly with regard to the exposure site. In this study, pulp exposure on the occlusal and mesial surfaces of molar teeth was investigated in a rat model. Materials and Methods: A total of 58 maxillary first molars of Wistar rats were used. Forty molars were mechanically exposed and randomly assigned according to 3 factors: 1) the exposure site (occlusal or mesial), 2) the pulp-capping material (ProRoot White MTA or Bio-MA), and 3) 2 follow-up periods (1 day or 7 days) (n = 5 each). The pulp of 6 intact molars served as negative controls. The pulp of 12 molars was exposed without a capping material (n = 3 per exposure site for each period) and served as positive controls. Inflammatory cell infiltration and reparative dentin formation were histologically evaluated at 1 and 7 days using grading scores. Results: At 1 day, localized mild inflammation was detected in most teeth in all experimental groups. At 7 days, continuous/discontinuous calcified bridges were formed at exposure sites with no or few inflammatory cells. No significant differences in pulpal response according to the exposure site or calcium-silicate cement were observed. Conclusions: The location of the exposure site had no effect on rat pulpal healing. However, mesial exposures could be performed easily, with more consistent results. The pulpal responses were not significantly different between the 2 capping materials.

Fluoride Wastewater Treatment using Waste Concrete Powder (폐콘크리트분말을 이용한 불산폐수 처리)

  • Kim, Eun-I;Kang, Wan-Hyup;Park, Joo-Yang
    • Journal of Korean Society of Water and Wastewater
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    • v.19 no.2
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    • pp.125-134
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    • 2005
  • Waste concrete powder was used to remove fluoride ions in highly concentrated fluoride wastewater. 92.6% of fluoride in 100 mg F/L wastewater was removed by 1% dose of the cement paste powder that represents characteristics of waste concrete powder, whereas the removal efficiencies of raw cement and lime were 47.3% and 96.4%, respectively. The cement paste powder was competitive to lime, common fluoride removal agent. Various Ca-bearing hydrates such as portlandite, calcium silicate hydrate, and ettringite in cement paste slurry can remove fluoride by precipitating $CaF_2$ and absorbing $F^-$ ions. In the experiments using both cement paste and lime, 50~67% of lime can be substituted by cement paste to satisfy fluoride effluent limitation of 15 mg/L. Since cement paste has higher acid neutralization capacity than lime, it can be recycled to neutralize more acid and to remove more fluoride. Therefore waste concrete powder can be more economical and viable alternative for lime in fluoride wastewater treatment.

Improving the CO2 Sequestration Capability and Mechanical Properties of CO2 Reactive Cement Paste Using pH Swing Method (pH Swing법을 활용한 이산화탄소 반응경화형 시멘트 경화체의 CO2 고정화 성능 및 기계적 물성 개선)

  • Cho, Seong-Min;Kim, Gyeong-Ryul;Bae, Sung-Chul
    • 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.

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Effect of polyolefin fibers on the permeability of cement-based composites

  • Hsu, Hui-Mi;Lin, Wei-Ting;Cheng, An
    • Computers and Concrete
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    • v.9 no.6
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    • pp.457-467
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    • 2012
  • This study evaluates the permeability of cement-based composites, which are a mix of polyolefin fibers and silica fume. Test results indicate that permeability increases as the water/cementitious ratio increases. Silica fume in cement-based composites produced hydrated calcium silicate and filled the pores. However, permeability decreased as the addition of silica fume increased. Specimens containing polyolefin fibers also provided higher permeability resistance. The polyolefin fiber length did not have a significant effect on permeability. The decrease in the permeability is mainly due to the addition of silica fume and lower water/cementitious ratio. Addition of fibers marginally decreases the permeability. Incorporating polyolefin fiber and silica fume in composites achieved more significant decreases in permeability. The correlated test results reveal the interrelationship between them.

Fluidity and Compressive Strength Properties of Cement-Mortar admixed with II-Anhydrite and Pozollanic Fine Powders (불산부생 II -형 무수석고와 포졸란 미분체가 혼입된 시멘트.몰탈 유동성 및 압축강도 특성)

  • 김도수;김재호;조민형;전진환;남재현;노재성
    • 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.

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Finite Element Analysis of the Effect of Chloride Ion on the Coastal Concrete Structure with Ground Granulated Blast Furnace Slag (고로슬래그 미분말을 사용한 해양콘크리트 구조물의 염분침투해석)

  • 여경윤;김은겸
    • Proceedings of the Korea Concrete Institute Conference
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    • 2000.10b
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    • pp.945-950
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    • 2000
  • Coastal concrete structure is harmed by physical and chemical action of sea water, impact load, meteorological effect and etc. especially, premature reinforcement corrosion in concrete exposed to sea water has an important problem. In this study, the behavior of chloride ions penetrated through the coastal concrete structure with ordinary portland cement or ground granulated blast furnace slag(GGBFS) was modeled. The physicochemical processes including the diffusion of chloride and the chemical reaction of chloride ion with calcium silicate hydrate and the other constituents of hardened cement paste such as$C_3A$ and $C_4AF$were analyzed by using the Finite Element Method. From analysis result, the corrosion of concrete structure with GGBFS begins 1.69~1.76 times later than that of concrete structure with ordinary portland cement.

Evaluation of Setting Time, Solubility, and Compressive Strength of Four Calcium Silicate-Based Cements (네 가지 규산 칼슘계 시멘트의 경화시간, 용해도, 압축강도 평가)

  • Yuji Jang;Yujin Kim;Junghwan Lee;Jongsoo Kim;Joonhaeng Lee;Mi Ran Han;Jongbin Kim;Jisun Shin
    • Journal of the korean academy of Pediatric Dentistry
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    • v.50 no.2
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    • pp.217-228
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    • 2023
  • This study aimed to compare the physical properties of 4 kinds of calcium silicate-based cements (CSCs): 2 kinds of powder-liquid mix type (RetroMTA® [RTMX] and Endocem® MTA Zr [EZMX]) and 2 kinds of premixed type (Well-RootTMPT [WRPR] and Endocem® MTA premixed [ECPR]) CSCs, respectively. Further, we assessed the setting times, solubility values, and compressive strengths of the cements. The shortest setting time was observed for EZMX (123.33 ± 5.77 seconds), followed by RTMX (146.67 ± 5.77 seconds), ECPR (260.00 ± 17.32 seconds), and WRPR (460.00 ± 17.32 seconds), respectively. The highest solubility was observed for WRPR (9.01 ± 0.55%), followed by RTMX (2.17 ± 0.07%), EZMX (0.55 ± 0.03%), and ECPR (0.17 ± 0.03%). Furthermore, the highest compressive strength was observed for ECPR (76.67 ± 25.67 Mpa), followed by WRPR (38.39 ± 7.25 Mpa), RTMX (35.07 ± 5.34 Mpa), and EZMX (4.07 ± 0.60 Mpa). In conclusion, the premixed type CSCs (WRPR and ECPR) exhibited longer setting times compared to the powder-liquid mix type CSCs (EZMX and RTMX). The solubility test showed that ECPR had the lowest solubility while WRPR had the highest solubility, with a statistically significant difference between them (p < 0.0083). Additionally, the compressive strength test showed that ECPR had the highest compressive strength, while EZMX had the lowest compressive strength, also with a statistically significant difference between them (p < 0.0083). ECPR is a promising material as it is premixed, eliminating the need for mixing time, and it has also demonstrated improved solubility and compressive strength, making it a potentially favorable option for clinical use.

Optical sensitivity of DNA-dispersed single-walled carbon nanotubes within cement composites under mechanical load

  • Kim, Jin Hee;Rhee, Inkyu;Jung, Yong Chae;Ha, Sumin;Kim, Yoong Ahm
    • Carbon letters
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    • v.24
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    • pp.90-96
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    • 2017
  • We demonstrated the sensitivity of optically active single-walled carbon nanotubes (SWCNTs) with a diameter below 1 nm that were homogeneously dispersed in cement composites under a mechanical load. Deoxyribonucleic acid (DNA) was selected as the dispersing agent to achieve a homogeneous dispersion of SWCNTs in an aqueous solution, and the dispersion state of the SWCNTs were characterized using various optical tools. It was found that the addition of a large amount of DNA prohibited the structural evolution of calcium hydroxide and calcium silicate hydrate. Based on the in-situ Raman and X-ray diffraction studies, it was evident that hydrophilic functional groups within the DNA strongly retarded the hydration reaction. The optimum amount of DNA with respect to the cement was found to be 0.05 wt%. The strong Raman signals coming from the SWCNTs entrapped in the cement composites enabled us to understand their dispersion state within the cement as well as their interfacial interaction. The G and G' bands of the SWCNTs sensitively varied under mechanical compression. Our results indicate that an extremely small amount of SWCNTs can be used as an optical strain sensor if they are homogeneously dispersed within cement composites.

A micro-computed tomography evaluation of voids using calcium silicate-based materials in teeth with simulated internal root resorption

  • Tek, Vildan;Turker, Sevinc Aktemur
    • Restorative Dentistry and Endodontics
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    • v.45 no.1
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    • pp.5.1-5.8
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    • 2020
  • Objectives: The obturation quality of MTA, Biodentine, Total Fill BC root canal sealer (RCS), and warm gutta-percha (WGP) in teeth with simulated internal root resorption (IRR) was evaluated by using micro-computed tomography. Materials and Methods: Standardized IRR cavities were created using 40 extracted maxillary central incisor teeth and randomly assigned into 4 groups (n = 10). IRR cavities were filled with MTA, Biodentine, Total Fill BC RCS (bulk-fill form) and WGP + Total Fill BC RCS. Percentage of voids between resorptive cavity walls and obturation material (external void), and inside the filling materials (internal voids) were measured. Results: Total Fill BC sealer in the bulk-fill form presented significantly highest values of external and internal void percentages (p < 0.05). Biodentine showed a significantly lowest external void percentage (p < 0.05). WGP + Total Fill BC RCS presented significantly lower values of internal void percentages than all groups (p < 0.05), except Biodentine (p > 0.05). Conclusion: None of the filling materials were created void-free obturation in resorption cavities. Biodentine may favor its application in teeth with IRR over Angelus MTA and bulkfill form of Total Fill BC.