Fly Ash in Self-Compacting Concrete

The importance of a low water cement ratio for enhancing durability of concrete has long been accepted. Low water content leads to a low workability of the fresh concrete and if this concrete is not properly compacted, the durability of the structures will be impaired. In the mid seventies, superplasticizers were introduced to the market to produce rheoplastic concretes. These concretes had a high workability, slump of over 200 mm, but were at the same time cohesive and non segregating. Millions of cubic meters of such concretes have been used all over the world during this decade. Recently self-compacting concrete was developed in Japan and its use is spreading very rapidly to other countries. A proper design of a self-compacting concrete requires considerably more fines content as compared to the traditional concrete. Therefore, large volumes of fly ash, partially in substitution of cement and partially as filler, can be employed in producing self-compacting concrete. This paper compares the properties of fresh and hardened normal concrete and a self-compacting concrete with large volumes of fly ash. Significant advantages in the use of fly ash are demonstrated.