Internal Composition of 20-Year-Old Fly Ash and Slag-Blended Ordinary Portland Cement Pastes

Pozzolanic materials have been used as an extender in concrete for more than half a century, providing various degrees of durability against chemical attack. Most studies use short term data to develop thermodynamic models to predict long term performance. This paper presents data on OPC and OPC blended cements at 30% replacement with either Class F fly ash or blast furnace slag that have been cured under controlled conditions for 20 years. The aqueous phase composition was characterized in terms of Na(+), K(+), Ca(2+), Si(4+), Al(3+), Mg(2+) and Cl(-). DTA, XRD and a combination of scanning and transmission electron microscopy along with energy dispersive X-ray analysis on argon-milled sections were used to determine the mineralogy and microstructure of the solid phase assemblage.