Section Six
SOLIDIFICATION, STABILIZATION, AND
COMBUSTION RESIDUES
62    CEMENTITIOUS PROPERTIES OF ATMOSPHERIC
FLUIDIZED BED COMBUSTION RESIDUES AND
THEIR USE IN ENGINEERING APPLICATIONS
R.T. Hemmings, Vice President
E.E. Berry, President
Radian Canada Incorporated
Mississauga, Ontario, Canada
INTRODUCTION
Atmospheric pressure fluidized bed combustion (AFBC) is gaining acceptance for the utilization of
"problem" fuels, such as low grade or high-sulfur coals, for thermal power generation. However, it
has become increasingly clear that the management of the AFBC by-products can impose a major
obstacle to the future development of the technology on a large scale. The development of FBC
technology has entered the medium-term phase during which research on the application of residues
can be started, an effort that will form the basis for future commercial utilization.1 Although considerable research has been conducted and utilization options have been proposed for AFBC byproducts, commercial applications have not been established to date.2,3
The various uses investigated for AFBC by-products have included numerous attempts to incorporate them in some form of concrete, frequently in combination with portland cement. As part of a
comprehensive evaluation of potential uses of AFBC materials, in 1984, Berry2 concluded that their
composition was incompatible with portland cement concrete in structural applications. In 1985, Rose
et al.4 examined a range of portland cement-based concrete mixes containing spent bed discharge
material from the TVA 20 MWe bubbling AFB combustor at Shawnee. These authors concluded that
such concretes may have commercial potential in underground mine applications where extended
setting times and expansion are acceptable.
AFBC residues contain unreacted lime (CaO) and calcium sulfate (CaS04), both of which react
exothermically with water and are potential sources of expansive reactions in cemented systems.
Further, because of their composition, residues from limestone sorbents, rather than showing pozzo-
lanic action, are more likely to provide the lime component necessary to induce pozzolanic reactivity
in a fly ash or natural pozzolan.3,5
Recognizing the limitations of the materials, a novel approach to the use of AFBC by-products was
reported in 1986 by Rose et al.6 during studies conducted by TVA and the Kentucky Energy Cabinet.
This approach involved the production of what was termed "no-cement" concretes from co-utilization
of FBC by-products in combination with conventional pulverized fuel fly ash (PFA). The PFA in
these mixes was introduced, ostensibly, to act as a "pozzolan" through reactions with CaO from the
spent bed residue. Also, to mitigate the temperature rise and to reduce the expansive potential of the
FBC by-products, the spent bed residue was prehydrated with ~ 10% by mass of water.
The above studies were all conducted on mixes made with spent bed materials from the TVA AFBC
pilot plant and two different PFA samples, also from TVA sources (Shawnee Steam and Kingston
Plants). For these materials, it was found that specific proportions of constituents (i.e., 1 part PFA to
2.1 parts AFBC spent bed residue to 3.4 parts coarse limestone aggregate) produced optimal, workable concretes at 4-to 5-inch slump, with compressive strengths over 5,100 psi after 60 days of curing.
Subsequent work by Bland7 suggested that the ratio Ca(OH)2 to PFA is a chemical factor related to
the optimum properties of no-cement binders. All of the studies conducted on the TVA materials were
49th Purdue Industrial Waste Conference Proceedings, 1994 Lewis Publishers, Chelsea, Michigan 48118. Printed in
U.S.A.
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