Development of high volume fly ash cements for use in concrete construction

The paper describes a study undertaken to examine the use of high levels of low-lime fly ash (high volume FA) as a cement component in concrete, beyond the 30% level commonly adopted. The results indicate that FA levels up to 45% by mass can be combined with Portland cement (PC, C1) to produce the range of practical concrete design strengths, although early strength, which may be critical in construction, can be reduced compared to PC, and lower level FA concretes. The study progressed to consider the use of a rapid hardening Portland cement (C2) and low energy clinker (C3) combined with FA at 45%, as a means of overcoming these early strength shortfalls. Both were found to be effective in matching early strength behaviour of PC concrete. Tests covering fresh (workability loss, bleeding and moisture loss), engineering (strength development, modulus of elasticity, drying shrinkage and creep) and durability (absorption, permeability, carbonation rates and chloride diffusion) properties of these concretes were then carried out. The results indicate that in almost all cases, either similar or enhanced performance was achieved with the high volume FA concrete, compared to that of PC and these findings offer a route to extending FA use. The practical implications of the study are also examined.