ASTM E2243-13(2019)

4.3.1.1 Fly ash is typically lighter than the fill soil it replaces, with unit weight ranging from about 50 to 100 pcf (8 to 16 kN/m³).

4.3.1.2 Bottom ash is also typically less dense than coarse-grained soils of similar gradation, with unit weight ranging from about 70 to 90 pcf (11 to 14 kN/m³).

4.3.1.3 Boiler slag is typically as heavy as, if not heavier than, natural soils of similar gradation, with unit weight ranging from about 90 to 110 pcf (14 to 18 kN/m³).

4.3.1.4 Oxidized and/or fixated FGD materials are also relatively lightweight, with unit weights ranging from about 50 to 100 pcf (8 to 16 kN/m³).

4.3.2.1 Fly ash, FGD material, and FBC ash are typically placed and compacted in a manner similar to noncohesive fine-grained soils. Smooth-drum vibratory rollers or pneumatic tired rollers typically compact these materials most effectively. Although not always, fly ash and FGD material typically exhibit a measurable moisture-density relationship that can be utilized for compaction quality control. To take full advantage of the self-hardening properties of some fly ash, FGD material, and FBC ash, compaction soon after the addition of water is recommended. If hardening or cementation has occurred prior to compaction, cementitious bonds may need to be disrupted to relocate the grains into a more dense state 4.3.2.2 Bottom ash is generally placed and compacted in a manner similar to noncohesive coarse-grained soils or fine aggregate. Smooth-drum vibratory rollers typically are most effective for the compaction of these materials. Bottom ash may or may not exhibit consistent moisture-density relationships. Bottom ash typically compacts best when saturated. Bottom ash should be compacted to a specified density.

4.3.2.3 Boiler slag is generally placed and compacted in a manner similar to noncohesive coarse-grained soils or fine aggregate. Smooth-drum vibratory rollers typically are most effective for the compaction of these materials. As with bottom ash, boiler slag may or may not exhibit consistent moisture-density relationships. Boiler slag typically compacts best when saturated.

4.3.3.1 Shear Strength—For non-self-hardening fly ash and bottom ash, shear strength is derived primarily from internal friction. Typical values for angles of internal friction for non-self-hardening fly ash are higher than those for many natural soils. These ashes are non-cohesive, and although the ash may appear cohesive in a partially saturated state, this effect is lost when the material is either completely dried or saturated.

4.3.3.2 Compressive Strength—Self-hardening CCPs and stabilized FGD material undergo a cementing process that increases with time. Hydration of dry self-hardening CCPs commences immediately upon exposure to water and can cement the CCP particles in a loose state, reducing the compacted density and strength. High compressive strengths can be achieved if the CCPs are compacted immediately after incorporation of water. Unconfined compressive strengths greater than 2000 psi have been reported for a cementitious ash-water mixture after 248 days (18).

4.3.4.1 Bottom ash and boiler slag are free-draining materials that can be compacted into a relatively dense, incompressible mass. For this reason, structural fills constructed of bottom ash or boiler slag also typically exhibit small amounts of time-dependent, postconstruction consolidation or deformation, with the most deformation occurring during construction.

4.3.4.2 Self-hardening fly ash and FGD material typically exhibit minimal postconstruction consolidation or deformation because of cementing and solidification of the CCPs.

4.3.5.1 The permeability values for non-self-hardening fly ash are similar to those observed for natural silty soils.

4.3.5.2 Self-hardening fly ash and FGD material are relatively impermeable, with permeability values similar to those for natural clays. Self-hardening fly ash and some FGD material may be susceptible to cracking in the environment. Cracking can produce a conduit for liquids through the placed material and change the measured permeability.

4.3.5.3 Bottom ash and boiler slag are typically as permeable as granular soils of similar gradation.

4.3.6.1 Internal Erosion (Piping)—Non-self-hardening fly ash is subject to internal erosion because of its fine-grained, noncohesive nature. Internal erosion can be controlled by providing adequate surface water controls to minimize infiltration and by providing internal drainage when warranted.

4.3.6.2 Surface Erosion—All CCPs may be eroded by wind or water and require use of erosion controls similar to those commonly used on earthwork construction projects. Wind erosion may be controlled by use of wind breaks. Dusting may be controlled by addition of water, or conditioning, to non-self-hardening materials. Water erosion can be limited by controlling water at the site by using sedimentation, sloping, and run-off controls meeting regulatory requirements. These controls should be put in place under the supervision of a qualified professional.

4.3.8.1 Well-compacted bottom ash and boiler slag are not typically susceptible to either liquefaction or frost heave. However, some of the finer bottom ash materials may behave quite similarly to fly ash and would require the same consideration for design as fly ash embankments.

4.5.1.1 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 occurs 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:

4.5.1.2 State and Local—There is considerable variation in state-mandated permitting and other regulatory requirements for CCP utilization. Some states have specific beneficial use policies, while other states have no regulations or guidance addressing beneficial use. Although the NEPA (National Environmental Policy Act) strictly applies only to federally funded projects, many states have similar mechanisms for assessing the environmental impacts of non-Federal projects. These mechanisms may require state permits that address any or all of the following issues: wetlands/waterways, National Pollutant Discharge Elimination System (NPDES) discharge, underground injection, erosion and sediment control, air quality considerations, and storm water management.

4.5.2.1 Ground Water—The design and implementation of a mine reclamation project should consider the potential ground water impacts of CCPs to ensure the protection of human health and the environment. Considerable research has been conducted to assess and predict the potential impacts of CCP utilization on ground water quality. An assessment of ground water quality impacts should be performed by a qualified professional and should take into account project-specific considerations such as composition of CCPs, the typically limited leachability of CCPs, presence of acid forming materials or acid mine drainage, placement of CCPs relative to the ground water table, rates of infiltration, the type of placement used for the CCP, and constituent migration, attenuation in ground water, and location of sensitive receptors (that is, wells). Where protection of ground water is a special concern, the leaching characteristics of the CCP should be evaluated as part of the assessment of constituent migration and attenuation. Consideration should be given to the leachability of the CCP in the presence of AMD. Some states may require a groundwater protection plan be prepared outlining controls that will limit potential impact to groundwater.

4.5.2.2 Surface Water—CCPs may affect surface water bodies during and after placement activities as a result of erosion and sediment transport. The engineering and construction practices recommended to minimize these effects on surface waters include storing the CCPs in stockpiles employing effective storm water management controls to maximize runoff and minimize run-on.

4.5.3.1 Dust Control—Dusting must be controlled during the transport and handling of CCPs in order to avoid fugitive dust and to ensure worker safety. Dust control measures routinely used on earthwork projects are effective in minimizing airborne particulates at CCP storage sites. Typical controls include appropriate hauling methods, use of windbreaks, moisture conditioning of the CCPs, storage in bins or silos, covering the CCPs with large tarpaulins, wetting or covering exposed CCP surfaces, and paving or wetting unpaved high-traffic haul roads with coarse materials.

4.5.3.2 Radionuclides—Coal and fly ash are not significantly enriched in radioactive elements or in associated radioactivity compared to common soils or rocks (21). Certain radioactive elements including radium and uranium are known to occur naturally in CCPs 4.6 Economic Benefits—The use of CCPs for mine reclamation can have economic benefits. These benefits are affected by local and regional factors, including production rates, processing and handling costs, transportation costs, availability and cost of competing materials, environmental concerns, and the experience of materials specifiers, design engineers, purchasing agents, contractors, legislators, regulators, and other professionals. CCPs are competing as manufactured materials and not as waste products, however in the event that CCPs do not meet beneficial use requirements or cannot be utilized, they should be managed at an appropriate waste facility. Since CCPs are produced in the process of manufacturing electricity, these materials can present an advantage when utilized as raw products for finished goods. This is primarily due to the low overheads involved with the material production cost and the fact that some, but not all coal-fired power plants have immediate access to low-cost transportation. The transport of coal to the power plant can provide an excellent opportunity to return CCPs to a mine site to aid in mine reclamation projects.