Reducing Embodied Energy in Masonry Construction

Fly ash unit masonry requires less energy and emits less CO2 during manufacturing, and contains more recycled content than conventional clay and concrete units.
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Sponsored by CalStar Products, Inc.
Peter J. Arsenault, FAIA, NCARB, LEED-AP

By contrast, manufacturing of fly ash bricks is focused on using recycled post-industrial materials with no kiln firing and no cement. These bricks are typically made up of 60% sand that is locally quarried plus 40% fly ash received from a local power plant. These two materials are used instead of clay and shale with significantly less environmental impact. The fly ash and sand are mixed together along with water, some additives, and pigments for brick coloration. The material is then vibro-compacted into molds of the desired size, texture, and shape. The fly ash is the binding agent that holds the mixture together. From there, the units are moved into curing chambers, where they cure in a sauna-like environment overnight, dramatically reducing the processing time and the amount of energy used, as compared with conventional clay brick. Once removed from the curing chambers, the units are packaged for delivery to the marketplace. The resulting differences between fly ash brick and clay brick include:

  • Recycled content: Fly ash bricks typically have 40% recycled content while clay bricks typically do not possess much recycled content.
  • Embodied energy: a modular fly ash brick contains about 1,000 BTUs of embodied energy while a modular clay bricks contains between 5,000 and 12,000 BTUs each. If one takes a middle-ground number of 6,000 BTU for each clay brick, it can be seen that fly ash bricks reduce manufacturing energy consumption by about 85%.
  • Emissions: The combustion of the fuel to fire clay bricks results in significant greenhouse gas emissions (predominantly CO2). Because fly ash bricks use about 85% less energy than conventional clay bricks, fly ash bricks are also responsible for about 85% less CO2.


FIGURE 4: Fly ash masonry is available in range of shapes, sizes, types and colors.

Image courtesy of CalStar Products, Inc.

There are multiple sustainable benefits of specifying fly ash brick instead of clay brick on a building project. For example, on a project that uses 100,000 bricks (on about 15,000 square feet of wall area), the use of fly ash bricks would eliminate approximately 500 million BTUs of energy consumption; reduce CO2 emissions by 40 tons; and would divert 78 tons of material from landfill. The reduction in CO2 emissions alone is equivalent to taking seven cars off the road for a year.

From a design standpoint, fly ash brick provide everything architects expect from a brick, except the carbon footprint. Fly ash bricks have been extensively tested and meet the performance requirements for severe weathering-grade brick (SW) in ASTM C216 Standard Specification for Facing Brick (Solid Masonry Units Made from Clay or Shale), though of course fly ash bricks are not made from clay or shale. Fly ash brick are installed the same way as conventional clay brick. They are compatible with standard Type N and Type S mortar. The same masonry ties are appropriately used here as with other brick installations. Movement joint location and detailing is the same as for any well-constructed building. Movement joints should be placed at large penetrations, near inside and outside wall corners, at changes in wall height and width, among other places. For fly ash bricks, movement joints along long unbroken spans should be placed every 20'. The weight, fire resistance, and thermal properties of fly ash brick are similar to clay and fly ash brick retains the comparable qualities of low maintenance. Fly ash brick have been installed in many locations around the United States with excellent results.

Currently, fly ash masonry is available in the following common sizes with custom sizes also possible:

  • Utility brick, nominally 4" x 4'" x 12"
  • Modular brick, nominally 4" x 2-1/4" x 8"
  • Facing units, nominally 4" x 8" x 24"
  • Structural brick, nominally 8" x 4" x 16" and 12" x 4" x 16"
  • Holland pavers, nominally 4" x 8" x 60mm
  • Permeable pavers, nominally 5" x 10" x 80mm

Fly Ash Brick Environmental Health & Safety

Fly ash itself and fly ash brick have been rigorously tested for environmental health and safety by independent testing laboratories. This includes leaching tests, such as the Toxic Characteristic Leaching Procedure (TCLP), which is the only EPA-approved method for determining if a material is a hazardous waste. The purpose of this test is to determine if compounds will leach out of a material at any levels of concern to health. This test simulates the aggressive environment of disposal in a municipal solid waste landfill. It is worth noting that construction debris typically winds up in a Construction and Demolition (C&D) landfill, which is a less aggressive condition. The testing for fly ash brick also includes Synthetic Precipitation Leaching Procedure (SPLP), which simulates exposure to acid rain.

Tests have also been performed on fly ash brick to determine if there are any particular concerns related to dermal (skin) contact with the product. The National Institute for Occupational Safety & Health (NIOSH) has developed a test for dermal (skin) contact with materials. An independent laboratory has looked specifically at fly ash bricks based on this test and determined that "the presence of CCR [fly ash] metals in newly manufactured bricks is not expected to result in any exposures of health concern via dermal contact with brick surfaces or via leaching."

Fly ash itself has been used safely for more than 80 years in building materials. In a typical year, more than 13 million tons of fly ash are beneficially recycled into building products. (See Figure 5) The largest beneficial use of fly ash is the inclusion in concrete mixes to replace a portion of the Portland cement in concrete. This can be seen and documented in old and new projects across the country: fly ash was used in the construction of the Hoover Dam, new Freedom Tower in New York City, the new section of the Bay bridge in San Francisco, the 1964 Marina Towers, and the 2010 Aqua Tower in Chicago, to name just a few high-profile projects. In general, fly ash is used in about 80% of all ready-mix concrete projects.

FIGURE 5: Fly ash brick can be used in a wide variety of buildings based on the more than 80-year history of fly ash use in building products.

Image courtesy of CalStar Products, Inc.

The EPA has spent significant effort in the past several years looking at how fly ash should be classified with respect to disposal, as problems can arise when millions of tons of ash are disposed of improperly in unlined ponds. (The majority of new fly ash is disposed of in properly lined landfills. All new landfills should be built to best management practices.) The EPA is considering regulating the disposal of fly ash under the Resource Conservation and Recovery Act (RCRA) Subtitle C, "Special Waste" or RCRA Subtitle D, "Solid Waste". In all cases, the EPA specifically states that beneficial reuse of coal combustion residuals (including fly ash)—such as recycling into concrete, bricks, wallboard, and other building products—will remain unregulated, and will continue to be promoted by the EPA. Environmental NGO's, including the Natural Resources Defense Council and Earthjustice, agree that beneficial reuse of fly ash is important and useful. In April of 2010, Mathy Stanislaus, assistant administrator for EPA's Office of Solid Waste and Emergency Response stated "EPA supports the legitimate beneficial use of coal combustion residuals (CCRs). Environmentally-sound beneficial uses of ash conserve resources, reduce greenhouse gas emissions, lessen the need for waste disposal units, and provide significant domestic economic benefits. This proposal will clearly differentiate these uses from coal ash disposal and assure that safe beneficial uses are not restricted and in fact are encouraged."

 

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Originally published in February 2012

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