Mitigation of ASR Expansion by Biomass/Coal Fly Ash and the Underlying Mechanism by Pore Solution Chemistry

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Title: Mitigation of ASR Expansion by Biomass/Coal Fly Ash and the Underlying Mechanism by Pore Solution Chemistry

Author(s): S. Wang, S. Bragonje, J. Tullis, R. Dalton, and L. Baxter

Publication: Special Publication

Volume: 242

Issue:

Appears on pages(s): 267-278

Keywords: alkali silica reaction; biomass fly ash; expansion; pore solution

Date: 4/1/2007

Abstract:
This investigation experimentally documents mitigation of alkali-silica-reaction (ASR) expansion through partial replacement of cement with coal-biomass cofired fly ash. ASTM C 227 and 441 guide the experimental techniques. Biomass and Class F fly ash reduce ASR expansion within 0.1% at the 6 month with 35% replacement ratio, although biomass fly ash has much higher available Na2Oequiv (by ASTM C 33). Further analysis of pore solution by high pressure extrusion illustrates that biomass fly ash mixes have similar alkali metal concentrations to Class C mixes, but biomass fly ash is at least equal or much better than Class C in mitigating ASR expansion; this implied that biomass fly ash may absorb alkalis from the pore solution and may form non-expansive products instead of the expansive alkali silica gel.