Title:
Use of Fly Ash Co-Mingled with Flue Gas Desulfurization Products as Alternative SCM
Author(s):
Farshad Rajabipour
Publication:
Web Session
Volume:
ws_S23_FarshadRajabipour.PDF
Issue:
Appears on pages(s):
Keywords:
DOI:
Date:
4/2/2023
Abstract:
A substantial fraction of fly ash co-mingled with flue gas desulfurization (FGD) products are discarded as off-specification materials due to exceeding the 5.0% SO3 content limit specified in ASTM C618. As such, it is expected that fly ash harvested from some landfills and ponds will have high SO3 content. The behavior of these fly ashes in cementitious systems varies significantly depending on the type of sulfur present in the ash including calcium sulfate, calcium sulfite, and sodium sulfate. As such, a single SO3 content limit specified in ASTM C618 is not sufficient to capture their complexity or performance. Four off-specification FGD co-mingled fly ash products were investigated in this study. This included evaluating their impact on workability, setting time, pore solution pH, compressive strength, and expansion in lime water using paste and mortar mixtures at 20% cement replacement level. Advanced characterization techniques such as X-ray diffraction, isothermal calorimetry, and pore solution analysis using inductively coupled plasma atomic emission spectroscopy were also used to study the hydration behavior of blended systems containing these ashes. The results of this study have been used to identify appropriate beneficiation options and potential modifications to the specifications.