• Computers and Concrete
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• 제22권5호
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• pp.481-492
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• 2018

In this paper, a new hybrid fiber system (NHFS) is investigated for the application of slab. The steel fiber, polyvinyl alcohol (PVA) fiber and calcium carbonate ($CaCO_3$) whisker is added to form NHFS. The four-point bending test is carried out on the flexural properties of slab with plain, steel fiber, traditional hybrid fiber system (THFS) and NHFS reinforced cementitious composites. The flexural behavior is evaluated by ASTM C1018-97, JCI-SF4 and post-crack strength (PCS) technique. The evaluation parameters of flexural toughness such as toughness index (TI), equivalent flexural strength (EFS) and PCS are determined. The size of slab specimens is $15mm(thickness){\times}50mm(width){\times}200mm(length)$. The results show that adding $CaCO_3$ whisker to THFS can significantly improve the flexural strength, TI, EFS, PCS of the slab. The empirical relation between reinforcing index ($RI_v$) and flexural parameters show that flexural parameters of slabs increase first and then decrease; which indicates that optimum $RI_v$ values can be helpful in the considering the mix design of steel-PVA fibers-$CaCO_3$ whisker composites for achieving the desired flexural-related properties. The scanning electron microscopy is performed to observe the micro-morphological characteristics of the fracture surface, which proved the positive hybrid effect among the different fibers in cementitious composites. The NHFS can arrest the generation and propagation of the crack from micro to macro level.

• 한국세라믹학회지
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• 제33권1호
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• pp.7-16
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• 1996

${CO_3}^{2-}$ containing whisker-like hydroxyapatite powders were synthesized byhomogeneous precipitation method using urea, Dicalcium phosphate anhdrate[DCPA; $CaHPO_4$] and octacalcium phosphate [OCP; $Ca_8H_2(PO_4_)6\cdot5H_20$]were obtained as precursors and they transformed to high crystalline hydroxyapatites at pH 5.62, and 6.54 respectively. According to the condition of the final pH in the solutions for the solution products and urea contents OCP was remained. When the solution product of $Ca^{2-}$ and ${PO_4}^{3-}$ was $1.5\times 10^4$[$mM^2$] and the content of urea was 0.25 mol.$dm^{-3}$ well crystallized whisker-like hydroxyapatite tens of micrometer in length was obtained. By heat treatment DCPA and OCP were decomposed into $\beta$-tricalcium phosphate [$\beta$-TCP ; $\beta$-$Ca_3{PO_4}_2$] and $\beta$-dicalcium phosphate [$\beta$-DCP ;$\beta$-$Ca_2P_2O_4}_2$]. And well-crystallized hydroxyapatite was partially decomposed into $\beta$-TCP at $800^{\circ}C$.

• 한국세라믹학회지
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• 제53권2호
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• pp.222-226
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• 2016

The synthesis of pure calcium carbonate nanocrystals was achieved using a simultaneous injection method to produce nano particles of uniform size. These were characterized using scanning electron microscopy and powder X-ray diffraction. The nano particles were needle-shaped aragonite polymorphs, approximately 100-200 nm in length. The aragonite polymorph of calcium carbonate was prepared using aqueous solutions of $CaCl_2$ and $Na_2CO_3$, which were injected simultaneously into double distilled water at $50^{\circ}C$ and then allowed to react for 1.5 h. The resulting whisker-type nano aragonite with high aspect ratio (30) is biocompatible and potentially suitable for applications in light weight plastics, as well as in the medical, pharmaceutical, cosmetic and paint industries.

• Computers and Concrete
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• 제31권3호
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• pp.197-206
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• 2023

In this paper, the bending performance of a MSFRHPC (containing steel fiber, polyvinyl alcohol (PVA) fiber, and CW)-reinforced beam was studied for the first time. Introducing a multiscale fiber system increased the first crack load (up to 150%), yield load (up to 50%), and peak load (up to 15%) of reinforced beams. The multiscale fiber system delays cracking of the reinforced beam, reduces crack width of the reinforced beam in normal use, and improves the durability of the beam. Considering yield load and peak load, the reinforcing effect of multiscale fiber on the high-reinforcement ratio beam (1.00%) is better than that on the low-reinforcement ratio beam (0.57%). Introducing fibers slowed the development of cracks in the reinforced beam under bending. With the added hybrid fiber, the deformation concentration of reinforced beams after yield was more significant with concentration in 1 or 2 cracks. A model for predicting the flexural capacity of MSFRHPC-reinforced beams was proposed, considering the action of multiscale hybrid fibers. This research is helpful for structure application of MSFRHPC-containing CW.

• 지질공학
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• 제13권2호
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• pp.239-256
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• 2003

이 연구에서는 대전지역 민방위 비상급수용 지하수의 수리화학적 특성을 밝히고 질소 및 황 동위원소를 분석하여 질산성 질소와 황산염의 기원을 해석하고자 하였다. 지하수의 수질화학적 특성은 전반적으로 약산성화 되어 있으며, 전기전도도 값은 $142~903{\;}\mu\textrm{S}/cm$의 범위로 평균 $352{\;}\mu\textrm{S}/cm$을 보인다. 지하수의 화학적 유형은 $Ca-HCO_3$ 형에서 Ca-Cl ($SO_4,NO_3$) 형까지 넓게 분포한다. 지하수의 $CO_2$ 함량과 pH에 의해 결정되는 $EpCO_2$ 값을 유기오염의 지수로 활용하였다. 지역별 지하수의 성분을 비교하고 성분별 농도분포를 알아보기 위하여 박스-휘스커(Box-Whisker) 다이아그램과 등치선도를 작성하였다. 수리화학적 자료를 종합하면 동구와 중구, 대덕구 일대 구도심권의 지하수가 약산성의 높은 전기전도도 특성과 높은 $NO_3$, $SO_4$, $EpCO_2$ 분포를 보여 서구와 유성구에 비해 오염이 많이 진행된 상태를 보인다. 지하수 22개 시료에 대한 ${\delta}^{15}N$ 분석 값은 서구와 유성구의 지하수에서 ${\delta}^{15}N$ 값이 $+7.4~+9.6{\textperthousand}$ 범위를 보여 지하수내 질산성질소 오염은 생활하수의 가능성이 높다. 그리고 동구, 중구, 대덕구 등 구도심권 지하수의 ${\delta}^{15}N$ 값은 $+10.2~+23.5{\textperthousand}$의 범위를 보여 정화조에서의 누출수가 주요 오염원일 가능성이 있다. 그리고 지하수의 ${\delta}^{34}S$ 값은 $+3~13.4{\textperthousand}$의 범위를 보인다. 일부 지하수 시료는 황산염 환원반응을 거쳐 $10{\textperthousand}$이상의 높은 ${\delta}^{34}S$ 값을 보이고, $7{\textperthousand}$ 내외의 ${\delta}^{34}S$ 값을 보이는 지하수는 황철석과 대기기원 외에도 인위적 오염에 의한 황 성분의 유입 가능성을 배제할 수 없다.