• Title/Summary/Keyword: Expansion Method

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Discussion on the Current Mortar-bar Method (ASTM 0227-90) by Experimental Study (실험적 연구에 의한 현행 모르타르봉 시험법(ASTM C227-90)의 검토)

  • 정지곤;이동영;유신애;황형중
    • The Journal of Engineering Geology
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    • v.6 no.3
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    • pp.155-163
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    • 1996

  • The current ASTM C227-90 is a prescription on the mortar-bar method. This recornrnends that mortar-bars should be made using a mixing ratio by weight of 675 grams aggregate to 300 grams cement, and their initial lengths should be measured in $24{\pm}2$ hours. This method emphasizes that the prepare sample mortar-bars and calculate expansion rates of them. This method requires constant G values (effective gauge lengths) of denominator in the calculation formula, which are fixed either at 10 inches or 250mm. This study, based on experimental approaches, reexamines the suggestions made by those two prescriptions above and important results are summarized in the following. 1. Not only alkali-aggregate reaction but also interaction of interstitial and gel water are responsible for expansion of mortar-bars. This requires partial modification of the current ASTM C227-90. 2. A mixing ratio by volume rather than by weight of aggregate to cement is recommendable for measuring the amount of expansion resulting from alkali-aggregate reaction and from interstitial water. 3. The method of when to measure initial lengths and how to calculate expansion rate suggested by ASThI C227-90 and Cl90-93a should partly be modified for more accurate results.

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Analysis of Offset Dual Reflector Antennas Using the Zernike Polynomials (Zernike 다항식을 이용한 오프셋 복 반사경 안테나의 해석)

  • Hak Kuen Choi
    • Journal of the Korean Institute of Telematics and Electronics A
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    • v.28A no.9
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    • pp.662-670
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    • 1991

  • Fast analysis method for calculating the radiation pattern of offset dual reflector antenna are presented. The validity of proposed method was verified by comparing with results of PO/PO, GO/PO, and the equivalent paraboloid method. Proposed method is the series expansion method using the Zernike polynomials. The calculated results by using the Zernike polynomials are in good agreement with obtained results by GO/PO and equivalent paraboloid method except PO/PO.

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