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6 internal sulfate attack, appear quite unlikely. Type III port- containing just fly ash, portland cement, and water), most land cement has been successfully used in CLSM to achieve CLSM contains fine aggregate (most commonly concrete sand). higher early strengths and to reduce subsidence. Only a small percentage of CLSM used in practice contains coarse aggregate. Supplementary Cementitious Materials Concrete Sand Fly Ash A wide range of fine aggregates may be used successfully in About 62 million tons of fly ash, a by-product of coal com- CLSM, but conventional concrete sand (ASTM C 33) is the bustion, were estimated to have been generated in 2001. Fly most common, especially for CLSM produced at ready-mixed ash is used mostly in portland cement concrete, but its use in concrete plants (the dominant source of CLSM). Sand that CLSM has grown considerably in recent years. Although fly does not meet ASTM C 33 requirements (e.g., gradation) ash has become an important construction material, approx- can be and often times has been used in CLSM production, imately 70 to 75 percent of the fly ash generated annually is still disposed in landfills (FHWA 1997). Much of this unused provided that the specified flowability and constructability fly ash does not meet specifications for use in portland cement requirements are satisfied. concrete (ASTM C 618), sometimes because of high percent- ages of unburned carbon, as measured by the loss on ignition Foundry Sand (LOI) test. Fortunately, it has been demonstrated that CLSM can be successfully produced using a wide variety of fly ash Foundry sand, a by-product of the metal-casting industry, types and sources, including high-carbon fly ash that is not has been studied and used successfully in CLSM and its use typically permitted in concrete. Both Class F and Class C fly has increased in recent years (Bhat and Lovell 1996; Tikalsky ash (according to ASTM C 618) are commonly used in CLSM, et al. 1998). Foundry sand is becoming a more viable candi- as well as ashes that do not conform to ASTM C 618. date for use in CLSM because of its lower cost, increasing The use of fly ash in CLSM provides for excellent flowabil- availability, and satisfactory performance. It is estimated that ity and helps to minimize segregation, as well as reduces the for every ton of metal castings produced and shipped that a cost of the mixture (as fly ash is typically less costly than port- typical foundry generates approximately one ton of waste sand land cement). Fly ash is used in higher dosages in CLSM than (Kennedy and Linne 1987). in conventional concrete mixtures; typically fly ash composes A concern with using foundry sand in CLSM is the poten- more than half the binder, and in the case of rapid-setting tial for environmental impact caused by leaching of heavy CLSM, fly ash is used as the only binder, without portland ce- metals present in the foundry sand. Therefore, ferrous ment. Based on the 1998 survey of current practice (Folliard foundry sands are more commonly used in CLSM because of et al. 1999), of the forty-two states specifying CLSM, twenty- the concerns about the heavy metals content of nonferrous seven states had specifications for CLSM containing fly ash, foundry sands. The most commonly used waste foundry sand and eleven states allow fly ash that did not meet ASTM C 618 in CLSM is "green sand," a term applied when the original specifications to be used in CLSM. sand is treated with a bonding agent (usually clay) to optimize More specific information on types and dosages of fly ash the efficiency of the sand in the molding process. used in typical CLSM mixtures is provided later in this chap- ter, and the laboratory and field evaluations described in Chap- Bottom Ash ters 3 and 4 included the use of a range of different fly ashes. Bottom ash and fly ash are both by-product materials of coal combustion. Bottom ash is formed by large noncombustible Other Supplementary Cementitious Materials particles that cannot be carried by the hot gases. These parti- Although fly ash is the most commonly used supplemen- cles descend on hoppers or conveyors, at the bottom of the tary cementitious material (SCM) in CLSM, other SCMs can furnace, in a solid or partially molten condition. Then, the and have been used. Materials such as slag, metakaolin, silica particles gradually cool to form bottom ash. Bottom ash parti- fume, and rice husk ash are all suitable for use in CLSM. cles are typically porous and angular in shape. As a by-product material, bottom ash is commonly disposed of in ponds. In this process, bottom ash is passed through a crusher to reduce the Aggregates size of large particles and is transported hydraulically through Various aggregate types have been used successfully in pipelines to the pond shore. The typical range of particle sizes CLSM. With the exception of CLSM paste mixtures (typically falls between 75 m and 25 mm. Researchers and practitioners