Title:
Quantitative Analysis of Fly Ash Hydration Products Formed in Sulfate Environment
Author(s):
Rajaram Dhole, Michael D.A. Thomas, Kevin J. Folliard, Thano Drimalas
Publication:
Symposium Paper
Volume:
362
Issue:
Appears on pages(s):
412-431
Keywords:
ettringite, fly ash, hydration products, monosulfate, scanning electron microscopy, X-ray diffraction
DOI:
10.14359/51740900
Date:
6/11/2024
Abstract:
Investigations were made into the hydration products formed by the fly ashes before and after exposure to sulfate solutions, and the impact of hydration products on the sulfate resistance of concrete. Pastes of selected Class C and Class F fly ashes were prepared by blending each fly ash with calcium hydroxide and a solution of sodium and potassium hydroxide. The quantities of ettringite, monosulfate, and portlandite formed in the paste samples at 28 days were determined by semi-quantitative X-ray diffraction analysis (XRD) using rutile as an internal standard. Subsequently, pastes were exposed to sulfate solutions of sodium and calcium in different concentrations for 90 days. At the end of 90 days, quantities of hydration products in the pastes subjected to sulfate solutions were determined by using the Rietveld method of analysis. In the second part of the program, mortar bars were exposed to sulfate solutions and examined by scanning electron microscopy (SEM) to determine the presence and location of sulfate reaction products namely ettringite, gypsum, and monosulfate. The degree of decalcification undergone by paste located in different zones in the mortar specimens was determined by measuring the CaO/SiO2 (C/S, ratio) using SEM coupled with ‘electron dispersive X-ray analysis’ (EDXA).