| Budget Amount *help |
¥7,100,000 (Direct Cost: ¥7,100,000)
Fiscal Year 1989: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1988: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 1987: ¥5,900,000 (Direct Cost: ¥5,900,000)
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| Research Abstract |
Basic problems related to the new method of mixing concrete under a reduced pressure (MURP method) and properties of mortar and concrete produced by the method were studied, expecting that air-entrained concrete of high strength and high freeze-thaw durability may be produced if air bubbles in fresh concrete behave In accordance with the Boyle's law.
The followings are main findings or conclusions.
1. The rate of water loss from mixing materials under water vapor pressure is dependent mainly on the capacity of evacuating system. However, even when evacuated to such a low pressure, the total amount of water lost through the use of ordinary vacuum pumps during the required evacuating time and mixing time is negligible compared with the water content in actual mortar or concrete mixes, and the temperature of the mixes is not altered.
2. When cement paste, mortar or concrete is mixed by MURP method keeping the dosage of AE agent constant, nearly the same amount of air as that by ordinary mixing method is entrained, and the entrained air behaves in a similar way as can be expected by Boyle's law. However, in the cases of mortar and concrete, the expected effects are impaired after their exposure to the atmospheric conditions, due to the intrusion of air into the mixtures from their surroundings during their discharging from mixer and/or agitation.
This undesirable phenomenon becomes prominent as the content of aggregate is increased.
As the result, the expected effects through the use of MURP method are reduced to nearly a half in the case of mortar, and to negligible extent in the case of concrete.
3. Concrete produced by MURP method has characteristics of low losses of air and slump with time. Its air loss under vibration is also lower compared with ordinary concrete.
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