INTERIM FINAL TECHNICAL REPORT
November
1, 1999, through October 31, 2000
Principal Investigator: Sankar Bhattacharja, Construction
Technology Laboratories (CTL), Inc.
Other
Investigators: James L. Evanko,
M.E. Tile Co.
Project
Manager: Ronald H. Carty, ICCI
The
overall objective of the project is to utilize fly ash, produced by burning
Illinois coal, which is currently being landfilled (due to lack of resource
utilization), as a major raw ingredient to manufacture value-added ceramic
tiles and to commercialize the technology.
Several steps are necessary to achieve
this objective. Initially, a
laboratory-scale investigation was conducted to validate the concept. The scale-up to a commercial tile
manufacturing facility and addressing the manufacturing methods, processing
parameters, and product qualities has been the focus of the subsequent
programs. During this period, ceramic tiles containing more than 60% fly ash were
successfully made. These fly ash tiles
exhibited lower firing shrinkage and water absorption than those of the
standard clay and talc-based tiles manufactured by a commercial tile
manufacturer in Illinois collaborating in this project.
In order to achieve the objective of
this project, a thorough investigation of the chemistry of the system was
necessary. Through this thorough
investigation, an effective processing method has been identified that does not
complicate the manufacturing process.
This approach downplays the compositional variability of fly ash, and
thereby provides a general applicability of the method developed, provided fly
ash characteristics do not vary significantly.
This concept has been successfully extended to overcome the problems
associated with the two processing methods being used. The
results obtained clearly indicate that fly ash can be utilized as the major raw
ingredient in successful manufacturing of ceramic tiles. The results also indicate that the
requirements for floor and outdoor applications are also achievable in the fly
ash-based system.
EXECUTIVE SUMMARY
The
fine particulate material that is electrostatically precipitated or
mechanically collected from the stack gases of power plants burning pulverized
coal is called fly ash. Annually, the
state of Illinois produces over 5% of the 60 million tons of fly ash generated
in the U.S. Approximately 20% of this
fly ash is utilized by the cement and concrete industry and the majority of the
rest is landfilled. Any non-concrete
utilization of the fly ash currently being disposed will not only be
environmentally sound and cost effective, but also will create a stable
year-round demand.
The
overall objective of this project is to utilize fly ash generated by the
burning of Illinois coal as the major raw ingredient for manufacturing
value-added ceramic tiles for wall, floor, and outdoor applications. Considering the size of the tile industry, a
considerable fraction of the fly ash produced in Illinois can be utilized to
prepare ceramic tiles. As raw materials
contribute to the major cost in running a tile plant, replacement of costly raw
materials by fly ash is attractive to tile manufacturers. Such utilization is environmentally
attractive, and the state economy will benefit from such an undertaking.
The
four steps that are envisioned as a necessity to prove this concept and
commercialize this technology are the following: Step I - laboratory-scale
investigation to validate the concept; Step II - scale-up investigation in a
commercial tile manufacturing facility; Step III - address the parameters and
develop data necessary for commercialization of this technology; and Step IV -
implementation of this technology to manufacture commercial tiles.
Step
I had been completed, and ceramic tile bodies with characteristics superior or
similar to wall and floor tiles were produced in the laboratory. Steps II, III, and IV are
interrelated and have been the focus of 1997-1999 and the present program. These
steps are being carried out at a commercial tile manufacturing plant located in
the State of Illinois, and fly ash-based tiles were manufactured with
characteristics similar to those of commercial tiles. The parameters
investigated in these programs were selected based upon what is necessary for
commercial manufacturing of fly ash-based tiles. Development of such information is essential for
commercialization of this technology.
The properties of commercial tiles are
specified in the American National Standard Specifications for Ceramic Tiles
(ANSI A137.1), published by the Tile Council of America (TCA). According to ANSI A137.1, tiles can be
glazed or unglazed, and the performance requirements vary depending upon the
application. Commercially, green tile bodies are manufactured using three processing
methods, dry pressing, wet pressing, and slip casting.
In dry pressing, approximately 5% water
is added based upon the weight of solid.
The floor, wall, and outdoor tiles produced in this method mostly have a
flat surface, and the production rate for this method is very high. In wet pressing, the amount of water used is
relatively higher (approximately 22 to 28%), and the resulting material has the
consistency of putty. This procedure
has the advantage of reasonably high production rates, and simple designs are
adequately reproduced. In the slip
casting method, a self-supporting shape, called a cast, is produced from a
specially formulated slip. Any
intricate designs can be adequately reproduced in this processing method. However, a number of parameters play an
important role in successful slip casting, which is even more complex in the
presence of the multimineralic nature of fly ash.
Upon
sintering of the green tile body, which forms solid bonds between particles,
the tile body is glazed at a relatively lower temperature. Glazing improves the surface durability and
adds different aesthetic values to tiles.
A glaze is a glassy material designed to melt on the surface of a
ceramic body, and to stay adhered upon cooling. In order to achieve a defect-free surface, it is important that
the thermal expansion of the glaze must be equal or slightly more than that of
the ceramic body. Among other
properties, breaking strength and water absorption are the most important
properties to determine the quality and applications of ceramic tiles.
Several tiles were made in the previous
programs with different colors and textures.
The firing shrinkage of the fly ash tiles was less than that of the clay
and talc-based tiles, indicating superior dimensional stability. The parameters necessary for
commercialization were also investigated by varying the amounts of fly ash and
other additives. Upon extensive
investigation of the chemistry of the system, an effective processing method
has been identified that can be used for plants with medium production
capacity. In addition, this approach
also minimizes the influence of compositional variability of fly ash in
day-to-day tile production and quality control.
The
present program was designed to refine this technology that has been proven to
be achievable in a commercial tile manufacturing plant. Processing methods and parameters that are
relevant to commercialization of this technology were emphasized in this
present program, including presentation at technical meetings. Several processing methods are also being
investigated in this program.
The results obtained during the last
twelve months of the present program demonstrate that high dosages of fly ash
can be used in successful commercial manufacturing of ceramic tiles using wet
pressing, and slip casting processing methods.
The cause of a few problems relevant to processing and aesthetics have
been identified and remedial measures developed. The test results indicate
that characteristics of fly ash-based tiles are far superior to those required
for wall tile applications, and comparable to those required for floor and
outdoor applications. Several fly ash
tile bodies have also passed the standard freeze/thaw test used in the tile
industry, indicating potential for floor and outdoor applications. Also, the processing method developed has
general applicability to other Class F fly ashes, although some specific
processing steps may need adjustments due to significant shifts in the fly ash
characteristics.