• Journal of the Korea Concrete Institute
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• v.15 no.3
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• pp.497-503
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• 2003

Supplementary cementitious materials (SCM) such as fly ash, ground granulated blast furnace slag and silica fume are now being extensively used in concrete to control expansion due to alkali-silica reactivity (ASR). However, the replacement level of a single SCM needed to deleterious ASR expansion and cracking may create other problem and concerns. For example, incorporating silica fume at levels greater than 10％ by mass of cement may lead to dispersion and workability concerns, while fly ash can lead to poor strength development at early age, The combination of silica fume and fly ash in ternary cementitious system may alleviate this and other concerns, and result in a number of synergistic effects. The aim of the study was to enable evaluation of more realistic suitability of a silica fume-fly ash combination system for ASR resistance based on an in-house modification of ASTM C 1260 test method. The modification can be more closely identified with actual field conditions. In this study three different strengths of NaOH test solution(1N, 0.5N, and 0.25N) were used to measure the expansion characteristics of mortar bar made with a reactive aggregate. The other variable included longer testing period of 28 days instead of a conventional 14 days.

• Microbiology and Biotechnology Letters
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• v.4 no.3
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• pp.99-104
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• 1976

Experiments were carried out to establish the effects of acids in neutralization after alkaline treatment of rice straw, with which cellulosic single cell protein can be produced by cellulose utilizing bacteria, Cellulomonas flavigena KIST 321, previously isolated by authors. Following results were obtained. 1. Rice straw as carbon source was pretreated with 10 volumes of 1 normality of NH$_4$OH or NaOH(NaOH/substrate：40％, and then washed with water or neutralized with H$_3$PO$_4$, H$_2$SO$_4$, HCl and CH$_3$COOH. Among the above mentioned methods, neutralization with H$_3$PO$_4$after alkaline treatment was proved to be the most effective on its digestibility and SCP production. Dry cell 12.28g/$\ell$ and 78％ digestibility were obtained. 2. When rice straw was treated with NaOH solution, the result suggested that the productibity of cell-mass was attained on treatment of rice straw with 6％ of NaOH (NaOH/substrate ratio) for 15～24hrs at room temperature. 3. When rice straw was treated with NaOH, a volume of water to substrate is adequate by two or three fold and the amount of NaOH can be economized up to 5％ for the weight of rice straw. 4. The steaming of rice straw at 121$^{\circ}C$ for 30min. in alkaline treatment of rice straw gave the similiar effectiveness to that at room temperature for 15～24hrs. and accelerated the sterilization of the substrate. 5. Finally, the level of inorganic phosphate in a medium was investigated. 11.2g of dry cell was produced at the concentration of 0.2％, phosphate (phosphorous level 0.04％) in medium even though treated rice straw was neutralized with HCI instead of H$_3$PO$_4$, and 12.2g/$\ell$ at the concentration of 0.3％ phosphate (phosphorous 0.04％) on neutralization with H$_2$SO$_4$.