| Project/Area Number |
61460215
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
農業土木
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| Research Institution | Iwate University |
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Principal Investigator |
TAKAHASHI Kazuo Faculty of Agriculture, Iwate University, 農学部, 教授 (60003737)
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| Co-Investigator(Kenkyū-buntansha) |
FUJII Koichi Faculty of Agriculture, Iwate University, 農学部, 助教授 (00032574)
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| Project Period (FY) |
1986 – 1988
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| Project Status |
Completed (Fiscal Year 1988)
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| Budget Amount *help |
¥7,600,000 (Direct Cost: ¥7,600,000)
Fiscal Year 1988: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 1987: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 1986: ¥5,200,000 (Direct Cost: ¥5,200,000)
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| Keywords | Precast Concrete / Frost Damage / Entrained Air / Freezing and Thawing / Vibration / Bubble / 蒸気養生 / 硬化コンクリート / AEコンクリート / 耐凍性 / 間隔係数 / コンクリート既製品 / 空気量 / 耐久性 / 硬化したコンクリートの性質 / 圧縮強度 / スランプ / 水セメント比 / 最大寸法(粗骨材) |
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| Research Abstract |
1. Enen in steamecured concrete, the entrained air provides a large resistance against deteriortion by freezing and thawing. Such a high resistance was also demonstrated even in the sample molded with 2-stage curing a day and a short pre-curing time.
2. No conrelation was noted between the compressive strength and durability of concrete. The durability of precast concrete depends completely on the entrained air.
3. The bubble area on the surface of precast concrete expands by repetition of freezing and thawing. However, airentrained precast concrete did not collapse even after 300 cycles of freezing and thawing. In contrast, plain concrete collapsed after only 90 cycles.
4. The present experiment results indicate that 6.5% is the limit of the entrained air content in an unhardened state of precast concrete.
5. A high resistance to freezing and thawing may not always be obtained even in air-entrained concrete that had the air content ot 4.5% in the unhardened state, if the air content was r
… More
educed by vidration.
6. An approximately 50% decrease in the air content during vibration on the vibration table as actually measured in a precast concrete plant occurred after 1 minute of vibration for plain concrete with 2.1% air content, after 2 minutes of vibration for air-entrained concrete with 4.5% air content and after 4 minutes of vibration for air-entrained concrete with 6% air content. With an narrower amplitude of vibration, the rate of the decrease in the air content was reduced to approximately 1/.
7. The entrained air content in hardened concrete measured in this experiment ranged from the minimum of 2.5% and maximum of 3.8%.
8. The measurement revealed that the mean air void fraction of bubbles was 220mu. Even the sample having the maximum air void fraction of 254mu demonstrated an adequate freezi-resistance.
9. The grain size accumulation of bubbles was predominated by air bubbles of the size below 100-200mu. This may suggest that these micro-bubbles have an effect of preventing deterioration of concrete due to frost damage. Less
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