Title: Hydration in High-Volume Fly Ash Concrete Binders

Author(s): Edwin E. Berry, Ray T. Hemmings, Min-Hong Zhang, Bruce J. Cornelius, and Dean M. Golden

Publication: Materials Journal

Volume: 91

Issue: 4

Appears on pages(s): 382-389

Keywords: aluminate cements and concretes; binders (materials); chemical analysis; fly ash; hydration; microstructure; models; porosity; Materials Research

DOI: 10.14359/4054

Date: 7/1/1994

Abstract:
This paper presents a summary of work in progress on an examination of the hydration chemistry and microstructure of a paste prepared incorporating 58 percent of a typical ASTM Class F fly ash and a portland cement from U.S. sources, and a paste with portland cement only. Thermal analysis, x-ray diffraction, pore fluid extraction, and SEM have been employed to study cement and cement-fly ash pastes cured up to 180 days. High levels of nonevaporable water and removal of alkali ions from pore solutions in pastes cured for 7 to 14 days were found. Etching of fly ash particles and extensive deposition of reaction products at ash/matrix boundaries were evident in scanning electron micrographs. Together, these observations clearly demonstrate extensive participation by the fly ash in hydration and cementation reactions. However, despite the extensive reactivity, up to 180 days, many fly ash particles remain as intact pseudomorphs embedded in the hydrate mass. A model based on siloxane and siloxane hydrolysis, alkali ion exchange, and precipitation of calcium silicates, aluminates, and aluminosilicates is proposed to explain the observed processes.