Cast-Concrete Products Made with FBC Ash
and Wet-Collected Coal-Ash
Tarun R. Naik, F.ASCE
1
; Rudolph N. Kraus
2
; Yoon-moon Chun
3
; and Francois D. Botha
4
Abstract: Cast-concrete hollow blocks, solid blocks, and paving stones were produced at a manufacturing plant by replacing up to 45%
by mass of portland cement with fluidized bed combustion FBC coal ash and up to 9% of natural aggregates with wet-collected,
low-lime, coarse coal-ash WA. Cast-concrete product specimens of all three types exceeded the compressive strength requirements of
ASTM from early ages, with the exception of one paving-stone mixture, which fell short of the requirement by less than 10%. The
cast-concrete products made by replacing up to 40% of cement with FBC ash were equivalent in strength 89–113% of control to the
products without ash. The abrasion resistance of paving stones was equivalent for up to 34% FBC ash content. Partial replacement of
aggregates with WA decreased strength of the products. The resistance of hollow blocks and paving stones to freezing and thawing
decreased appreciably with increasing ash contents. The cast-concrete products could be used indoors in regions where freezing and
thawing is a concern, and outdoors in a moderate climate.
DOI: 10.1061/ASCE0899-1561200517:6659
CE Database subject headings: Recycling; Ashes; Concrete masonry; Durability; Concrete precast; Compressive strength;
Freeze-thaw; Concrete blocks.
Introduction
The quantities of coal fly ash, bottom ash, and flue gas desulfur-
ization FGD material generated in the United States in 2001
were approximately 62, 17, and 26 million tons, respectively. The
respective utilization rates were approximately 32, 34, and 28%
Kalyoncu 2003. Among the materials that were utilized, most of
the fly ash was used for cement-based products manufacturing,
while most of the FGD material generated from low-SO
x
tech-
nologies was used for gypsum-based wallboard manufacturing.
There is a significant lack of commercial cement-based products
that utilize FGD material. Due to the Clean Air Act Amendments
of 1990, the quantity of FGD material is expected to increase
significantly Kalyoncu 2003. Finding practical solutions to this
“ash problem” is essential because of shrinking landfill space,
environmental concerns, and increased public awareness.
Compared to conventional coal ash, relatively very little work
has been conducted to date in developing cement-based products
containing FGD material. Recent research studies ICF Technol-
ogy Incorporated 1988; ICF Northwest 1988; Clarke and Smith
1991; Naik et al. 1991, 1995, 1997a,b; Clarke 1993 have shown
various potential applications for FGD material. The University
of Wisconsin-Milwaukee Center for By-Products Utilization
UWM-CBU has conducted a number of research projects on
high-volume uses of both ASTM Class F and Class C fly ashes in
cementitious products for the last two decades. The UWM-CBU
has also worked on concrete using FGD material since the late
1980s Naik et al. 1991.
Fluidized bed combustion FBC ash is the ash produced by an
FBC boiler in which the coal and sorbent e.g., limestone mix-
ture is fluidized during the combustion process to allow removal
of sulfur gases ACAA 2003. Major uses of FBC ash in the
United States in 2004 were in soil modification/stabilization, min-
ing applications, waste stabilization/solidifiction, and structural
fills/embankments ACAA 2005. This research project was con-
ducted to develop manufacturing technology for the use of FBC
ash and wet-collected, low-lime, coarse coal-ash WA in dry-cast
concrete masonry products. Hollow blocks, solid blocks, and pav-
ing stones incorporating the ashes were manufactured at a com-
mercial manufacturing plant in Rockford, Ill.
Experimental Procedures
Materials
Type I portland cement ASTM C 150 was used in this research.
Fine crushed limestone and natural sand were used as fine aggre-
gates. Crushed limestone with a 9.5 mm nominal maximum size
was used as coarse aggregate. One source of FBC ash and one
1
FACI, Professor of Structural Engineering, and Academic Program
Director, Center for By-Products Utilization, Univ. of Wisconsin-
Milwaukee, P.O. Box 784, Milwaukee, WI 53201 corresponding author.
E-mail: tarun@uwm.edu
2
Assistant Director, Center for By-Products Utilization, Univ. of
Wisconsin-Milwaukee, P.O. Box 784, Milwaukee, WI 53201. E-mail:
rudik@uwm.edu
3
Postdoctoral Fellow, Center for By-Products Utilization, Univ. of
Wisconsin-Milwaukee, P.O. Box 784, Milwaukee, WI 53201. E-mail:
ymchun@uwm.edu
4
Project Manager, Coal Residuals Management at the Illinois Clean
Coal Institute, 5776 Coal Dr., Suite 200, Carterville, IL 62918. E-mail:
fbotha@icci.org
Note. Associate Editor: Nemkumar Banthia. Discussion open until
May 1, 2006. Separate discussions must be submitted for individual pa-
pers. To extend the closing date by one month, a written request must be
filed with the ASCE Managing Editor. The manuscript for this paper was
submitted for review and possible publication on May 25, 2004; approved
on September 13, 2004. This paper is part of the Journal of Materials in
Civil Engineering, Vol. 17, No. 6, December 1, 2005. ©ASCE, ISSN
0899-1561/2005/6-659–663/$25.00.
JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / NOVEMBER/DECEMBER 2005 / 659