1991 Volume 2 Issue 1 Pages 45-56
Characteristics of the boundary surfaces of mortar and coarse aggregates in concrete materially affect properties of the concrete. For the purpose of improving characteristics of the boundary surfaces the author devised a new type of reduced pressure mixer. With a view that this mixer will be effective for mixing of concrete containing the blast-furnace slag aggregates, which are composed of slag pasticles of irregular shape and relatively large porosity, the mechanism and effects of the mortar with the slag under reduced pressure were studied. The results are described here. In this mixing process the mortar and aggregates are mixed under reduced pressure near the vacuum. When the mixing has been completed, the mixer is pressured back in a moment to the atmospheric pressure to make the mortar adhere to the blast-furnace slag aggregates with pressure. As a result the adhesiveness water on the aggregates and the free water in the mortar are pressed in the aggregates, thus strengthening the combination of the mortar with the aggregates and improving quality of the mortar with increase of the water cement ratio. In addition about a half of the entrapped air is expelledin the above process, making the parts of mortar denser. The study results proved that the above mentioned improvement in the concrete structure by the reduced pressure mixing secures multifalious effects, such as decrease of bleeding, expansion of the elastic area owing to decrease of bond cracking, wide increase of static strength, and improvement in fatigue strength and water tightness.
