2013 Volume 24 Issue 3 Pages 149-159
As one method of improving the freeze-thaw resistance of concrete using moderate heat cement mainly used in concrete dams, we examined the effects of air stability entrained by AE agent. The amount of bleeding was changed from 0.15 to 0.50cm3/cm2 by mixing two types of fine aggregate, and the air content of fresh concrete was further adjusted from 4.5 to 8.0% by using three types of AE agent with different components. In each case using AE agent, the value of the air-void spacing factor tended to become larger owing to the increase of the amount of bleeding in fresh concrete with an air amount of less than 6.0%. However, freeze-thaw resistance was found to be highly dependent on the components of the AE agent. In the case of AE agents with durability factor of less than 60, the number of air voids less than 0.15mm in diameter was observed to be lower in the hardened concrete. These experiments confirmed that, although freeze-thaw resistance can be reduced because of the coalescence of bubbles in fresh concrete and defoaming due to bleeding, which reduces the number of fine air voids, some components of the AE agent were capable of suppressing this effect.
