RHEOLOGICAL STUDY OF BLENDED CEMENT CONCRETE

摘要

Concrete durability to a large extent depends on its mechanical strength, which in turn depends on the concrete mixture proportions as well on the placing conditions. In fact, concrete mechanical strength increases by decreasing the mixing water for a given cement amount, but the less the water is in the concrete mixture, the more the concrete placing is difficult due to its workability loss. In this way, fresh concrete rheology becomes the most critical factor in order to guarantee a workability level, achieved with the minimum water content, but high enough to avoid macro-voids, concrete segregation and bleeding appearance. This is the reason why self-compacting concrete, which can be placed without any vibration and with minimal workmanship contribution, appears to be the concrete for the future, able to ensure the required durability level for a given expected service life. Concrete self-compactability is generally achieved by adding to the mixture a certain amount of very fine particles as a filler, together with a viscosity modifying agent able to keep fresh concrete viscous enough to avoid bleeding and segregation. However, some fillers are able to give concrete self-compactability without the aid of a viscosity modifying agent, so these fillers may be considered as mineral additions for blended cements able to change concrete rheology. In this paper the rheological properties of fresh concrete are discussed focusing on concrete self-compactability and different fillers are compared on the basis of their ability to generate concrete self-compacting behaviour.