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Abstract
Processes that maximize utilization of industrial solid wastes are greatly needed.
Sodium hydroxide and sodium silicate solution were used to create alkali-activated
complex binders (AACBs) from class C fly ash (CFA) and other Ca-containing admixtures
including Portland cement (PC), flue gas desulfurization gypsum (FGDG), and water
treatment residual (WTR). Specimens made only from CFA (CFA100), or the same fly ash
mixed with 40 wt% PC (CFA60-PC40), with 10 wt% FGDG (CFA90-FGDG10), or with 10 wt%
WTR (CFA90-WTR10) had better mechanical performance compared to binders using other
mix ratios. The maximum compressive strength of specimens reached 80.0 MPa. Geopolymeric
gel, sodium polysilicate zeolite, and hydrated products coexist when AACB reactions
occur. Ca from CFA, PC, and WTR precipitated as Ca(OH)(2), bonded in geopolymers to
obtain charge balance, or reacted with dissolved silicate and aluminate species to
form calcium silicate hydrate (C-S-H) gel. However, Ca from FGDG probably reacted
with dissolved silicate and aluminate species to form ettringite. Utilization of CFA
and Ca-containing admixtures in AACB is feasible. These binders may be widely utilized
in various applications such as in building materials and for solidification/stabilization
of other wastes, thus making the wastes more environmentally benign.