Abstract
This Thesis traces the development of high flyash content concrete. This concrete contains a high proportion of flyash in the cementitious content, usually between 50 and 80% by volume. The concrete was initially developed as a roller-compacted hearting (or interior) concrete for dams. Concrete with a low workability, a low thermal (and non-thermal) movement, and relatively high tensile strain capacity was required. In 1976, the Author had proposed that this could be obtained by using a concrete with a high paste content and that the high paste content should be obtained by using large quantities of flyash and a low cement content. This concept was studied in depth during a CIRIA project, which is described. For roller-compacted concrete, the optimum proportion of flyash in the cementitious content was found to be between 70 and 80%. The properties of such a concrete were found to be suitable for use in dams. High flyash content concrete has now been proposed for two dams, one in America and the other in the U. K. In the Thesis, a trial mix programme is described which extended the concept of a high flyash content in concrete into the workability range of immersion vibration. During this study, it was postulated that there is a relationship between the flyash contribution to compressive strength and the water/cementitious ratio, in the same fashion as that proposed for cement by Abrams in 1912. It is shown that the contribution of flyash to strength is more sensitive to the water content than the contribution of the cement, and that the conventional methods of mix design for flyash in concrete may not be using flyash to its best advantage. The Thesis concludes with a description of a placement of high flyash content concrete in a road and storage area. The sub-base of the road was placed through a paver-finisher without roller compaction and was a concrete in which flyash made up 75 to 80% of the cementitious content. The pavement-quality concrete was compacted by immersion vibration and flyash made up 60 to 65% of the cementitious content. Both concretes were extensively tested and have performed very well. It is concluded that high flyash content concrete is a new material, and that it should have a use in many forms of Civil Engineering construction, in particular dams and roads. Usually, there are substantial economic advantages in such a use, and the long-term in-situ properties are generally better than those of similar conventional concretes.