Title: The Influence of Lightweight Aggregates Additions in Concrete Mixtures Containing Alkali-Aggregate Reactive Normalweight Aggregate
Author(s): T.W. Bremner, S.R. Boyd, T.A. Holm, and J.P. Ries
Publication: Symposium Paper
Appears on pages(s): 497-510
Keywords: aggregates; alkali-aggregate reaction; infilling of pores; microcracking; pozzolan; vesicular
The production of lightweight aggregates entails heating a silica-rich raw material, which is usually shale, clay or slate to about 1150°C. This heat treatment appears to activate the surface of the expanded aggregates so as to produce pozzolanic properties that reduce expansion due to alkali-aggregate reaction. When these heat-treated aggregates are incorporated into a concrete mixture, beneficial effects result that enhance the properties of the concrete. These effects are similar to, but of a significant lower magnitude, than when a pozzolan such as fly ash or silica fume is added to a concrete mixture. This is to be expected because expanded shale, clay and slate that have been ground to a fineness somewhat greater than that of portland cement have been supplied to the concrete industry as a pozzolan for some time. Also, it has been shown in micrographs that the vesicular nature of lightweight aggregates provides a space for any reactants that might form to precipitate without causing expansion.