ASTM E2278-13

4.2.1.1 Unit Weight—Unit weight is the weight per unit volume of material. Fly ash has a low dry unit weight, typically about 50 to 100 pcf (8 to 16 kN/m³). Bottom ash is also typically lighter than coarse grained soils of similar gradation. Stabilized FGD material from a wet scrubber and FGD material from a dry scrubber are also relatively lightweight, with unit weights similar to fly ash.

4.2.1.2 Strength—Shear strength is the maximum resistance of a material to shearing stresses. The relatively high shear strength of fly ash is beneficial for CCP flowable fill formulations requiring strengths sufficient to prevent mine subsidence. The shear strength of non-self-hardening fly ash is primarily the result of internal friction. Cementitious CCPs experience a cementing action that is measured as cohesion and increases over time, which results in high compressive strength. Unconfined compressive strengths in excess of 1000 psi can be achieved for cementitious CCPs.

4.2.1.3 Specific Gravity—Specific gravity is the ratio of the weight in air of a given volume of solids at a stated temperature to the weight in air of an equal volume of distilled water at a stated temperature. The particle specific gravity of fly ash is relatively low compared to that of natural materials, and generally ranges from 2.1 to 2.6.

4.2.1.4 Grain-Size Distribution—Grain-size distribution describes the proportion of various particle sizes present in a material. Fly ash is a uniformly-graded product with spherical, very fine grained particles.

4.2.1.5 Moisture Content—Moisture content is the ratio of the mass of water contained in the pore spaces of soil or rock material to the solid mass of particles in that material, expressed as a percentage. CCPs have almost no moisture when first collected after the combustion of coal. Power plant operators sometimes add moisture to facilitate transport and handling, a process termed “conditioning.”

4.2.1.6 Coefficient of Permeability—Permeability is the capacity of a material to transmit a liquid. When compacted to its maximum dry density, fly ash can have permeabilities ranging from 10 to 10^-3 gpd/ft² (10^-4 to 10^-7 cm/s). These permeabilities are comparable to natural silty soils.

4.2.2.1 Elemental Composition—The major elemental components of CCPs are silica, aluminum, iron, calcium, magnesium, sodium, potassium, and sulfur. These elements are present in various amounts and combinations dependent primarily on the coal and type of CCP. The elements combine to form amorphous (glassy) or crystalline phases. Trace constituents may include elements such as arsenic, boron, cadmium, chromium, copper, chlorine, mercury, manganese, molybdenum, selenium, or zinc.

4.2.2.2 Phase Associations—The primary elemental constituents of CCPs are present either as amorphous (glassy) phases or crystalline phases. Coal combustion fly ash is typically 70+ % amorphous material. FGD and FBC products are primarily crystalline, and the crystalline phases typically include lime (CaO), portlandite (Ca(OH)_{4.2.2.3 Free Lime Content—Free lime content varies among CCP sources and other potential activators (for example, lime kiln dust, cement kiln dust, quicklime, or Portland cement). Variability of free lime content in CCP sources is due to the type and efficiency of the emissions control technology that is used. FBC products typically contain up to 10 % free lime, while most Class F fly ash has no free lime content. The free lime content of other potential activators is also variable. For example, cement kiln dust typically ranges from 20 to 30 % free lime whereas quicklime contains 100 % free lime.}

4.2.2.4 Pozzolanic Activity—Most CCPs, with the exception of FGD material, are characterized as pozzolans due to the presence of siliceous or siliceous and aluminous materials that in themselves possess little or no cementitious value but will, in finely divided form and in the presence of moisture, chemically react with calcium hydroxide at ordinary temperatures to form compounds possessing cementitious properties.

4.2.2.5 Buffer Capacity—The buffer capacity of the CCP is important in maintaining the high pH that generally is a requirement for neutralizing acidic materials such as acid mine drainage or for minimizing acid formation from acid forming materials. The CCP must have enough buffer capacity to maintain the pH of the treated areas so the area remains stable over time and under environmental stresses. Test Methods C400 can be applied to evaluate the buffer capacity of the CCP. Determine the basicity factor for the CCP as noted in Test Method B of Test Methods C400.

4.3.1.1 Federal—The U.S. Department of the Interior Office of Surface Mining (OSM) is charged with the responsibility of ensuring that the national requirements for protecting the environment during coal mining are met and making sure the land is reclaimed after it is mined. When the use of CCPs happens at surface coal mines, state or federal coal-mining regulators are involved to the extent that SMCRA (Surface Mining Control and Reclamation Act) requires the mine operator to ensure that:

4.3.2 Water Quality—When planning to use CCPs for mine reclamation, one should consider the potential impacts on ground water and surface water to ensure protection of human health and the environment.

4.3.3 Air Quality—When planning to use CCPs for mine reclamation, one should consider the potential impacts to air quality including dusting and emissions.