- Email: [email protected]
Overview of Coal Ash use in the Usa
Environmental Aspects of Construction with Waste Materials JJJ.M. Goumans, H A . van &r S l w t and Th.G. Aalbers (Editors) @I994 Elsevier Science B.V. AN n g h ~ sreserved.
699
OVERVIEW OF COAL ASH USE IN THE USA
Samuel S. Tyson American Coal Ash Association 1913 I Street N.W. - Suite 600 Washington, DC, 20006 USA SUMMARY
This paper describes coal ash produced by electric utilities in the USA. An overview is presented of the various applications in which this coal ash is used. 1. INTRODUCTION
The American Coal Ash Association, Inc. (ACAA) is an organization of producers, marketers and other organizations involved with utilization of coal ash, or coal combustion byproducts (CCBs). ACAA’s goal since its founding in 1968 has been to gain recognition and acceptance of coal ash as an engineering material on par with competing virgin, processed and manufactured materials by advancing coal ash uses that are technically sound, commercially effective, and environmentally safe. The use of CCBs is affected by local and regional factors including production rates; processing, transportation and handling costs; availability of competing materials; and experience of materials specifiers, design engineers, purchasing agents, contractors, legislators, regulators and other professionals. 2. ANNUAL CCB SURVEY A n annual survey of electric utilities is conducted by ACAA to determine the quantities of CCBs produced and used in the United States (1). In 1992 approximately 82 million short tons (for metric tons multiply short tons by 0.9078) of CCBs were produced in the USA in the form of fly ash, bottom ash, boiler slag and flue gas desulfurization (FGD) material. Approximately twenty-five percent of the combined production of these byproducts was used, while the remainder went to disposal areas. The approximate use quantities for these by-products are summarized in Table 1.
Table 1. Use of Coal Combustion By-products [1992 data; million short tons] Tons Used ( % Use)
Fly Ash 13.1 (27%)
Bottom Ash 3.9 (28%)
Boiler Slag 3.1 (75%)
FGD By-product 0.3 (2%)
700 It is clear from survey data gathered by ACAA over the years that the annual use of CCBs represents a major continuing effort by a number of parties, including the electric utility producers of ash and their marketers. It is equally clear, however, that significant tonnages of coal ash are not used each year. Therefore it is essential for ACAA to promote the use of coal combustion byproducts in numerous applications that are technically sound, commercially effective and environmentally safe. 3. CCB USES
CCBs are engineering materials with uses similar to the uses for competing virgin, processed and manufactured materials. It is instructive to consider the total tonnages of CCBs (fly ash, bottom ash, boiler slag and FGD material) that are used in the four leading markets for coal ash based on ACAA's 1992 survey results. This information is presented in Table 2. Table 2.
Use of CCBs in the Four Leading Markets [1992 data; million short tons)
Markets
Amount
Cement and Concrete Products Structural Fills Road Base and Subbase Blasting Grit/Roofing Granule Other Markets Total CCB usage
*
7.9 2.7 2.4 2.1 5.2 20.3
% of Usaqe*
38.9% 13.2% 11.7% 10.2% 26.0% 100.0%
Total CCB usage was 20.3 million tons which was 24.8 percent of the 82.0 million tons produced.
This paper describes each of these four leading markets for CCBs which together account for 74 percent of total CCB use in the USA. Additionally, the several categories of CCB uses that make up the other markets are summarized. 3.1
Cement and Concrete Products 3.1.1
Tmical Concrete
In 1992 approximately 7.1 million short tons of coal fly ash was used in the USA in cement and concrete products (1). The amount of fly ash in typical structural concrete applications ranges from 15 to 35 percent by weight of the total cementitious material (cement plus fly ash), with amounts up to 70 percent for massive walls and girders, road bases and dams.
70 1
Various concrete mixtures are produced with coal fly ash including normal weight and lightweight concretes, high strength concrete, early strength concrete for form removal requirements, low-slumppaving concrete, controlled low strength material (CLSM), and architectural concrete. With the principal exception of high strength concrete, all of these fly ash concrete mixtures are routinely air-entrained for added workability and for resistance to freezing and thawing. A state-of-the-artreport on the use of coal fly ash in concrete has been prepared by the American Concrete Institute (ACI) (2). Fly ash for use in concrete is covered in an ASTM specification (3). 3.1.2 Mixture Proportioninq The selection of mixture proportions for fly ash concrete is accomplished through the use of the same standard practices that are applied to any portland cement concrete. A document detailing a standard practice for normal, heavyweight and mass concretes is available from ACI (4). The ACI document shows computations for fly ash content specified either as a weight percentage or as a volume percentage of the total cementitious material content. The first approach, using weight equivalency, is probably the most common method in use. If the trial batches with and without fly ash are made to have the same ratio of water to cementitious material, then, as demonstrated in the ACI example: w/cl
=
w/(c2 + f ) ; where w
=
weight of water,
cl= weight of cement only, c2= weight of cement when used with fly ash, and f
=
weight of fly ash.
Because many fly ashes will bring about a significant decrease in water demand for the mixture, an absolute volume calculation is used to determine the small increase in sand to accommodate this slight volume decrease. Similarly, because of the assumption in the above example that cl = (c2 + f), and because fly ash has a lower specific gravity than portland cement, the mixture with fly ash will have a slightly greater volume. Again, absolute volume calculations are used to determine the small reduction in sand to accommodate this slight volume increase.
702 3.1.3
Roller ComDacted Concrete and Concrete Road Bases
The amount of fly ash in roller compacted concrete and concrete road bases, and in dams and massive walls and girders may be 70 percent or more of the total cementitious material. In such mixtures, where the fly ash content exceeds the portland cement content by a weight ratio of two or more, substantially increased curing times may be needed before placing the structure in service. For typical paving applications the percentage of fly ash will frequently be from 20 to 35 percent by weight of total cementitious material content, and normal curing times can be applied. For roller compacted concrete in paving applications reference documents are available from the ACI (51, the American Society of Civil Engineers (6) and the U.S. Army Corps of Engineers ( 7 )( 8 ) . 3.1.4 Concrete Block and Pilse
Fly ash and bottom ash are used in the manufacture of concrete masonry units, i.e., concrete block. Fly ash, because of its contribution to workability, strength and durability, is an important ingredient in the stiff mixtures used for concrete block. Similar attributes are cited for the selection of fly ash as a component of the stiff concrete mixtures used for concrete pipe. The several ASTM specifications for concrete pipe allow the use of fly ash by reference to either ASTM C 618, as discussed above for typical concrete mixtures, and ASTM C 595 (9). The concrete pipe specifications from ASTM are available through the American Concrete Pipe Association in a three-ring binder for convenient updating (10). 3.1.5
Lishtweisht Assresate
An ACAA symposium publication contains a number of papers describing traditional as well as developing uses of coal combustion by-products (11). One developing market is the manufacture of pelletized lightweight aggregate from coal fly ash by incorporating chemical admixtures and either lime (12) or portland cement (13) as activators, and from a third process using These lightweight fly ash and coal cleaning mixtures (14). aggregates are produced without the use of heat energy for sintering, however there is another process that produces a sintered fly ash aggregate (15). The lightweight aggregates produced without sintering are used primarily in concrete block, however some may be used in non-structural and structural concretes. A sub-committee of ACI Committee 213, on lightweight aggregate and lightweight aggregate concrete, is collecting information for publication on lightweight byproduct aggregates.
703 3.1.6
Flowable Mixtures
ACI Committee 229 deals with certain flowable grout-like materials under a general designation, "Controlled Low Strength Materials" (CLSM) (16). Such materials have compressive strengths equivalent to well compacted soils and may represent a wide range of fly ash contents. Applications include but are not limited to: backfills, structural fills, insulating fills, road and slab base, trench bedding and so on. While flowable mixtures can be produced without fly ash, it is very easy demonstrate that economical mixtures with the most desirable characteristics, including flowability, cohesiveness, minimal bleeding, and controlled density, can be produced only with fly ash in combination with relatively small amounts of portland cement. The percentage of fly ash used in grout mixtures may be in a wide range from 20 to 95 percent by weight. To produce a flowable mixture having a flowable consistency without segregation of the constituents, coal fly ash is typically proportioned with portland cement and water, with or without aggregate or other fillers. Some fly ashes with hihg lime contents can be used to produce a flowable mixture without cement. The use of CLSM flowable mixtures is open to numerous innovative engineering solutions for everyday problems that would otherwise be viewed as traditional soils backfilling and foundations problems. Such mixtures help to achieve economies through reduced labor and inspection costs, and allow contractors to reduce or eliminate certain labor and equipment costs. 3.2 Structural Fill Numerous structural fill applications of CCBs have been designed, constructed and evaluated over the last several decades. A number of such projects are described in re-publishedpapers from the proceedings of ACAA's international symposia (17). Coal fly ash is readily available in many locations to be used as a borrow material in lieu of soils for the construction of fills. When fly ash is compacted in lifts, the resulting structural fill is capable of supporting parking lots, buildings and roadways. Moistened fly ash can be used alone for structural fill applications. As with ordinary soils, optimum and target moisture contents can be established, along with procedures for achieving required levels of compaction. Open trenches can be cut in the compacted, non-cemented, fly ash for the placement of building footings and for the installation of pipes and cables.
704
When used in structural fills and embankments, fly ash offers several advantages over soil and rock: Low Unit Weight--Thecompacted maximum dry density of fly ash is typically about 10 to 20 percent less than that of ordinary soils. Placing fly ash over weak, compressible foundation soils results in lower total settlement. High Shear Strength--One of the most significant characteristics of fly ash used as a fill material is its strength. Compacted fly ash is as strong or stronger than many compacted soils. Moisture Control--Althoughthe optimum moisture content of fly ash is greater than that of silty soils, the compaction behavior of fly ash is relatively insensitive to variations in moisture content when it is placed with a moisture content that is less than its optimum moisture content. 3.3
Road Base and Subbase
ACAA has published a manual on the design and construction of pavement systems incorporating fly ash stabilized bases. The project to produce the manual was reported at a 1988 meeting of the American Society of Civil Engineers (18) where advice and comments were solicited. The ACAA pavement manual (19) offers pavement design engineers, materials engineers, and construction managers guidance in the design and construction of low- to high-strength Ilpozzolanic stabilized mixturer1( IIPSM1l) base and subbase layers having coal fly ash in combination with activators, aggregates and water. Users can choose from three pavement thickness design methods included in this manual: o
Method A - Flexible pavement structural layer coefficients;
o
Method B - Mechanistic pavement design procedures, using resilient modulus values for the pavement layers;
o
Method C - A combination of Method A and Method B, using mechanistic concepts to determine pavement layer coefficients.
design
procedures
using
To capture the long-term service and cost-saving features of PSM design, the document details a mixture proportioning system, a thickness design procedure, and established mixing and construction techniques. The user can apply the contents of this manual with professional advice to produce satisfactory pavement structures of acceptable uniformity in accordance with typical specifications and quality requirements of individual departments of transportation.
705 3.4
Blastinq Grit and Roofins Granules
Blasting grit and roofing granule applications, with an annual usage of 2.1 million short tons in 1992 represents 10.2% of the total coal ash used in that year. This market is extremely important to the coal ash industry as high-quality blasting grit and roofing granules are in fairly constant demand. The largest users of blasting grit are the large shipyards that perform contract maintenance for the U.S. Navy and for commercial shipping lines. The other users of blasting grit are supplied by a small number of companies which collect, size and bag the boiler slag and distribute it in small lots to numerous locations for use. Because the boiler slag that can be used for blasting grit is typically limited to slag produced in wet-bottom cyclone boilers, the long-term supply of this material will be related to the life of those boilers. The use of boiler slag as a roofing granule is subject to some of the same limitations as found for blasting grit. The large investment in facilities and equipment are factors which make use of boiler slag for roofing granules a regional manufacturing application with shipments of a finished product in small lots to numerous locations for use by a multitude of individual users. Miscellaneous uses of boiler slag are found in several decorative aggregate applications. For example, boiler slag has been used as a sand-substitute in sandtraps on golf courses; as an aggregate in precast and cast-in-placeconcrete to which a surface treatment is applied to expose this visually attractive material; and in less glamorous uses such as a sand-substitute in ashtrays for public buildings. 3.5
Other Markets
The several market categogies which together consume annually about 5.2 million short tons of CCBs in the USA are: filler in asphalt; anti-skid material for snow and ice on roadways; grouting; coal mine applications; wallboard manufacture; waste stabilization and solidification; and other low-volume applications such as fillers in plastics and paints. 4. CONCLUSION
ACAA is committed to increasing the use of CCBs in technically sound, commercially effective and environmentally safe applications and will work to ultimately achieve full use of these materials.
706 5. REFERENCES 1.
1992 Coal Combustion Bv-product Production and Consumption, American Coal Ash Association, Inc., Washington, D.C., 1993, 1 page.
2.
Use of Flv Ash in Concrete, American Concrete Institute, Committee 226 Report, ACI Materials Journal, Detroit, September-October 1987, pages 381-409.
3.
Standard Specification for Flv Ash and Raw or Calcined Natural Pozzolan for Use As a Mineral Admixture in Portland Cement Concrete, ASTM C 618, American Society for Testing and Materials, Philadelphia, 1993, 3 pages.
4.
Standard Practice for Selectins Proportions for Normal. Heavweisht and Mass Concrete, Committee 211 Report, ACI Manual of Concrete Practice, Part 1, Detroit, 1989.
5.
Roller ComDacted Concrete Pavement, Publication C - 8 , American Concrete Institute, Detroit, 1987, 55 pages.
6.
Roller Compacted Concrete 11, Conference Proceedings, American Society of Civil Engineers, San Diego, February 29-March 2, 1988.
7.
Encrineerins and Desisn - Roller ComDacted Concrete, U.S. Army Corps of Engineers, Engineer Manual 1110-2-2006, 1985.
8.
Roller ComDacted Concrete (RCC) Pavement for Airfields, Roads, Streets and Parkins Lots, U.S. Army Corps of Engineers, Guide Specification 02520, 1988.
9.
Standard Specification for Blended Hydraulic Cements, ASTM C 595, American Society for Testing and Materials, Philadelphia, 1986, 5 pages.
10.
ASTM Standards for Concrete PiDe, Authorized reprints of the American Society for Testing and Materials, American Concrete Pipe Association, Vienna, VA, 1988.
11.
Proceedinss: Eishth International Coal Ash Utilization Svmposium, Volumes 1 and 2, CS-5362, Washington, D.C., Prepared by American Coal Ash Association, Published by Electric Power Research Institute, October 1987, 870 pages.
12.
Ibid., Hay, Peter, "Aardelite - An Economical Lightweight Aggregate from Fly Ash," Paper No. 57, 7 pages.
13.
Ibid., Styron, Robert W., "Fly Ash Lightweight Aggregate: The Agglite Process,Il Paper No. 58, 12 pages.
707
14.
Ibid., Burnet, George, "Experimental Studies of the Production of Lightweight Aggregate from Fly Ash/Coal Cleaning Refuse Mixtures," Paper No. 61, 17 pages.
15.
Pulverized Fuel Ash Utilization, Central Generating Board, England, 1972, 104 pages.
16.
Committee Rosters, Missions, Goals, and Activities, American Concrete Institute, Detroit, June 30, 1988, 142 pages.
17.
Structural Fill ADDlications of Coal Ash, American Coal Ash Association, Washington, DC, 1993, 100 pages.
18.
"Guidelines for Design and Construction of Pozzolanic Stabilized Base Course Mixtures", DisDosal and Utilization of Electric Utility Wastes, Session Proceedings, American Society of Civil Engineers, Nashville, May 1988, page 35-49.
19.
"ACAA Pavement Manua1,I' Recommended Practice: Coal Fly Ash in Pozzolanic Stabilized Mixtures for Flexible Pavement Systems, American Coal Ash Association, December 1991, 64 pages plus Appendix.
Electricity
699
OVERVIEW OF COAL ASH USE IN THE USA
Samuel S. Tyson American Coal Ash Association 1913 I Street N.W. - Suite 600 Washington, DC, 20006 USA SUMMARY
This paper describes coal ash produced by electric utilities in the USA. An overview is presented of the various applications in which this coal ash is used. 1. INTRODUCTION
The American Coal Ash Association, Inc. (ACAA) is an organization of producers, marketers and other organizations involved with utilization of coal ash, or coal combustion byproducts (CCBs). ACAA’s goal since its founding in 1968 has been to gain recognition and acceptance of coal ash as an engineering material on par with competing virgin, processed and manufactured materials by advancing coal ash uses that are technically sound, commercially effective, and environmentally safe. The use of CCBs is affected by local and regional factors including production rates; processing, transportation and handling costs; availability of competing materials; and experience of materials specifiers, design engineers, purchasing agents, contractors, legislators, regulators and other professionals. 2. ANNUAL CCB SURVEY A n annual survey of electric utilities is conducted by ACAA to determine the quantities of CCBs produced and used in the United States (1). In 1992 approximately 82 million short tons (for metric tons multiply short tons by 0.9078) of CCBs were produced in the USA in the form of fly ash, bottom ash, boiler slag and flue gas desulfurization (FGD) material. Approximately twenty-five percent of the combined production of these byproducts was used, while the remainder went to disposal areas. The approximate use quantities for these by-products are summarized in Table 1.
Table 1. Use of Coal Combustion By-products [1992 data; million short tons] Tons Used ( % Use)
Fly Ash 13.1 (27%)
Bottom Ash 3.9 (28%)
Boiler Slag 3.1 (75%)
FGD By-product 0.3 (2%)
700 It is clear from survey data gathered by ACAA over the years that the annual use of CCBs represents a major continuing effort by a number of parties, including the electric utility producers of ash and their marketers. It is equally clear, however, that significant tonnages of coal ash are not used each year. Therefore it is essential for ACAA to promote the use of coal combustion byproducts in numerous applications that are technically sound, commercially effective and environmentally safe. 3. CCB USES
CCBs are engineering materials with uses similar to the uses for competing virgin, processed and manufactured materials. It is instructive to consider the total tonnages of CCBs (fly ash, bottom ash, boiler slag and FGD material) that are used in the four leading markets for coal ash based on ACAA's 1992 survey results. This information is presented in Table 2. Table 2.
Use of CCBs in the Four Leading Markets [1992 data; million short tons)
Markets
Amount
Cement and Concrete Products Structural Fills Road Base and Subbase Blasting Grit/Roofing Granule Other Markets Total CCB usage
*
7.9 2.7 2.4 2.1 5.2 20.3
% of Usaqe*
38.9% 13.2% 11.7% 10.2% 26.0% 100.0%
Total CCB usage was 20.3 million tons which was 24.8 percent of the 82.0 million tons produced.
This paper describes each of these four leading markets for CCBs which together account for 74 percent of total CCB use in the USA. Additionally, the several categories of CCB uses that make up the other markets are summarized. 3.1
Cement and Concrete Products 3.1.1
Tmical Concrete
In 1992 approximately 7.1 million short tons of coal fly ash was used in the USA in cement and concrete products (1). The amount of fly ash in typical structural concrete applications ranges from 15 to 35 percent by weight of the total cementitious material (cement plus fly ash), with amounts up to 70 percent for massive walls and girders, road bases and dams.
70 1
Various concrete mixtures are produced with coal fly ash including normal weight and lightweight concretes, high strength concrete, early strength concrete for form removal requirements, low-slumppaving concrete, controlled low strength material (CLSM), and architectural concrete. With the principal exception of high strength concrete, all of these fly ash concrete mixtures are routinely air-entrained for added workability and for resistance to freezing and thawing. A state-of-the-artreport on the use of coal fly ash in concrete has been prepared by the American Concrete Institute (ACI) (2). Fly ash for use in concrete is covered in an ASTM specification (3). 3.1.2 Mixture Proportioninq The selection of mixture proportions for fly ash concrete is accomplished through the use of the same standard practices that are applied to any portland cement concrete. A document detailing a standard practice for normal, heavyweight and mass concretes is available from ACI (4). The ACI document shows computations for fly ash content specified either as a weight percentage or as a volume percentage of the total cementitious material content. The first approach, using weight equivalency, is probably the most common method in use. If the trial batches with and without fly ash are made to have the same ratio of water to cementitious material, then, as demonstrated in the ACI example: w/cl
=
w/(c2 + f ) ; where w
=
weight of water,
cl= weight of cement only, c2= weight of cement when used with fly ash, and f
=
weight of fly ash.
Because many fly ashes will bring about a significant decrease in water demand for the mixture, an absolute volume calculation is used to determine the small increase in sand to accommodate this slight volume decrease. Similarly, because of the assumption in the above example that cl = (c2 + f), and because fly ash has a lower specific gravity than portland cement, the mixture with fly ash will have a slightly greater volume. Again, absolute volume calculations are used to determine the small reduction in sand to accommodate this slight volume increase.
702 3.1.3
Roller ComDacted Concrete and Concrete Road Bases
The amount of fly ash in roller compacted concrete and concrete road bases, and in dams and massive walls and girders may be 70 percent or more of the total cementitious material. In such mixtures, where the fly ash content exceeds the portland cement content by a weight ratio of two or more, substantially increased curing times may be needed before placing the structure in service. For typical paving applications the percentage of fly ash will frequently be from 20 to 35 percent by weight of total cementitious material content, and normal curing times can be applied. For roller compacted concrete in paving applications reference documents are available from the ACI (51, the American Society of Civil Engineers (6) and the U.S. Army Corps of Engineers ( 7 )( 8 ) . 3.1.4 Concrete Block and Pilse
Fly ash and bottom ash are used in the manufacture of concrete masonry units, i.e., concrete block. Fly ash, because of its contribution to workability, strength and durability, is an important ingredient in the stiff mixtures used for concrete block. Similar attributes are cited for the selection of fly ash as a component of the stiff concrete mixtures used for concrete pipe. The several ASTM specifications for concrete pipe allow the use of fly ash by reference to either ASTM C 618, as discussed above for typical concrete mixtures, and ASTM C 595 (9). The concrete pipe specifications from ASTM are available through the American Concrete Pipe Association in a three-ring binder for convenient updating (10). 3.1.5
Lishtweisht Assresate
An ACAA symposium publication contains a number of papers describing traditional as well as developing uses of coal combustion by-products (11). One developing market is the manufacture of pelletized lightweight aggregate from coal fly ash by incorporating chemical admixtures and either lime (12) or portland cement (13) as activators, and from a third process using These lightweight fly ash and coal cleaning mixtures (14). aggregates are produced without the use of heat energy for sintering, however there is another process that produces a sintered fly ash aggregate (15). The lightweight aggregates produced without sintering are used primarily in concrete block, however some may be used in non-structural and structural concretes. A sub-committee of ACI Committee 213, on lightweight aggregate and lightweight aggregate concrete, is collecting information for publication on lightweight byproduct aggregates.
703 3.1.6
Flowable Mixtures
ACI Committee 229 deals with certain flowable grout-like materials under a general designation, "Controlled Low Strength Materials" (CLSM) (16). Such materials have compressive strengths equivalent to well compacted soils and may represent a wide range of fly ash contents. Applications include but are not limited to: backfills, structural fills, insulating fills, road and slab base, trench bedding and so on. While flowable mixtures can be produced without fly ash, it is very easy demonstrate that economical mixtures with the most desirable characteristics, including flowability, cohesiveness, minimal bleeding, and controlled density, can be produced only with fly ash in combination with relatively small amounts of portland cement. The percentage of fly ash used in grout mixtures may be in a wide range from 20 to 95 percent by weight. To produce a flowable mixture having a flowable consistency without segregation of the constituents, coal fly ash is typically proportioned with portland cement and water, with or without aggregate or other fillers. Some fly ashes with hihg lime contents can be used to produce a flowable mixture without cement. The use of CLSM flowable mixtures is open to numerous innovative engineering solutions for everyday problems that would otherwise be viewed as traditional soils backfilling and foundations problems. Such mixtures help to achieve economies through reduced labor and inspection costs, and allow contractors to reduce or eliminate certain labor and equipment costs. 3.2 Structural Fill Numerous structural fill applications of CCBs have been designed, constructed and evaluated over the last several decades. A number of such projects are described in re-publishedpapers from the proceedings of ACAA's international symposia (17). Coal fly ash is readily available in many locations to be used as a borrow material in lieu of soils for the construction of fills. When fly ash is compacted in lifts, the resulting structural fill is capable of supporting parking lots, buildings and roadways. Moistened fly ash can be used alone for structural fill applications. As with ordinary soils, optimum and target moisture contents can be established, along with procedures for achieving required levels of compaction. Open trenches can be cut in the compacted, non-cemented, fly ash for the placement of building footings and for the installation of pipes and cables.
704
When used in structural fills and embankments, fly ash offers several advantages over soil and rock: Low Unit Weight--Thecompacted maximum dry density of fly ash is typically about 10 to 20 percent less than that of ordinary soils. Placing fly ash over weak, compressible foundation soils results in lower total settlement. High Shear Strength--One of the most significant characteristics of fly ash used as a fill material is its strength. Compacted fly ash is as strong or stronger than many compacted soils. Moisture Control--Althoughthe optimum moisture content of fly ash is greater than that of silty soils, the compaction behavior of fly ash is relatively insensitive to variations in moisture content when it is placed with a moisture content that is less than its optimum moisture content. 3.3
Road Base and Subbase
ACAA has published a manual on the design and construction of pavement systems incorporating fly ash stabilized bases. The project to produce the manual was reported at a 1988 meeting of the American Society of Civil Engineers (18) where advice and comments were solicited. The ACAA pavement manual (19) offers pavement design engineers, materials engineers, and construction managers guidance in the design and construction of low- to high-strength Ilpozzolanic stabilized mixturer1( IIPSM1l) base and subbase layers having coal fly ash in combination with activators, aggregates and water. Users can choose from three pavement thickness design methods included in this manual: o
Method A - Flexible pavement structural layer coefficients;
o
Method B - Mechanistic pavement design procedures, using resilient modulus values for the pavement layers;
o
Method C - A combination of Method A and Method B, using mechanistic concepts to determine pavement layer coefficients.
design
procedures
using
To capture the long-term service and cost-saving features of PSM design, the document details a mixture proportioning system, a thickness design procedure, and established mixing and construction techniques. The user can apply the contents of this manual with professional advice to produce satisfactory pavement structures of acceptable uniformity in accordance with typical specifications and quality requirements of individual departments of transportation.
705 3.4
Blastinq Grit and Roofins Granules
Blasting grit and roofing granule applications, with an annual usage of 2.1 million short tons in 1992 represents 10.2% of the total coal ash used in that year. This market is extremely important to the coal ash industry as high-quality blasting grit and roofing granules are in fairly constant demand. The largest users of blasting grit are the large shipyards that perform contract maintenance for the U.S. Navy and for commercial shipping lines. The other users of blasting grit are supplied by a small number of companies which collect, size and bag the boiler slag and distribute it in small lots to numerous locations for use. Because the boiler slag that can be used for blasting grit is typically limited to slag produced in wet-bottom cyclone boilers, the long-term supply of this material will be related to the life of those boilers. The use of boiler slag as a roofing granule is subject to some of the same limitations as found for blasting grit. The large investment in facilities and equipment are factors which make use of boiler slag for roofing granules a regional manufacturing application with shipments of a finished product in small lots to numerous locations for use by a multitude of individual users. Miscellaneous uses of boiler slag are found in several decorative aggregate applications. For example, boiler slag has been used as a sand-substitute in sandtraps on golf courses; as an aggregate in precast and cast-in-placeconcrete to which a surface treatment is applied to expose this visually attractive material; and in less glamorous uses such as a sand-substitute in ashtrays for public buildings. 3.5
Other Markets
The several market categogies which together consume annually about 5.2 million short tons of CCBs in the USA are: filler in asphalt; anti-skid material for snow and ice on roadways; grouting; coal mine applications; wallboard manufacture; waste stabilization and solidification; and other low-volume applications such as fillers in plastics and paints. 4. CONCLUSION
ACAA is committed to increasing the use of CCBs in technically sound, commercially effective and environmentally safe applications and will work to ultimately achieve full use of these materials.
706 5. REFERENCES 1.
1992 Coal Combustion Bv-product Production and Consumption, American Coal Ash Association, Inc., Washington, D.C., 1993, 1 page.
2.
Use of Flv Ash in Concrete, American Concrete Institute, Committee 226 Report, ACI Materials Journal, Detroit, September-October 1987, pages 381-409.
3.
Standard Specification for Flv Ash and Raw or Calcined Natural Pozzolan for Use As a Mineral Admixture in Portland Cement Concrete, ASTM C 618, American Society for Testing and Materials, Philadelphia, 1993, 3 pages.
4.
Standard Practice for Selectins Proportions for Normal. Heavweisht and Mass Concrete, Committee 211 Report, ACI Manual of Concrete Practice, Part 1, Detroit, 1989.
5.
Roller ComDacted Concrete Pavement, Publication C - 8 , American Concrete Institute, Detroit, 1987, 55 pages.
6.
Roller Compacted Concrete 11, Conference Proceedings, American Society of Civil Engineers, San Diego, February 29-March 2, 1988.
7.
Encrineerins and Desisn - Roller ComDacted Concrete, U.S. Army Corps of Engineers, Engineer Manual 1110-2-2006, 1985.
8.
Roller ComDacted Concrete (RCC) Pavement for Airfields, Roads, Streets and Parkins Lots, U.S. Army Corps of Engineers, Guide Specification 02520, 1988.
9.
Standard Specification for Blended Hydraulic Cements, ASTM C 595, American Society for Testing and Materials, Philadelphia, 1986, 5 pages.
10.
ASTM Standards for Concrete PiDe, Authorized reprints of the American Society for Testing and Materials, American Concrete Pipe Association, Vienna, VA, 1988.
11.
Proceedinss: Eishth International Coal Ash Utilization Svmposium, Volumes 1 and 2, CS-5362, Washington, D.C., Prepared by American Coal Ash Association, Published by Electric Power Research Institute, October 1987, 870 pages.
12.
Ibid., Hay, Peter, "Aardelite - An Economical Lightweight Aggregate from Fly Ash," Paper No. 57, 7 pages.
13.
Ibid., Styron, Robert W., "Fly Ash Lightweight Aggregate: The Agglite Process,Il Paper No. 58, 12 pages.
707
14.
Ibid., Burnet, George, "Experimental Studies of the Production of Lightweight Aggregate from Fly Ash/Coal Cleaning Refuse Mixtures," Paper No. 61, 17 pages.
15.
Pulverized Fuel Ash Utilization, Central Generating Board, England, 1972, 104 pages.
16.
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Electricity