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.

Peter J. Arsenault, FAIA, NCARB, LEED-AP

Brick has been a mainstay of building construction throughout history and continues to be one of the most favored building materials around the world. With sustainability becoming a basic requirement for all products and materials, conventional clay brick has come under increased scrutiny, in part due to the fossil fuel energy required to fire brick kilns and the associated CO₂ emissions. In response, a new type of brick has recently been introduced that does not require energy-intensive firing since it does not use clay. Instead, this technology utilizes the by-product of generating electricity from coal as the binder. The appearance, weight and performance characteristics of these new bricks are comparable to conventional clay bricks, but the new bricks possess significantly reduced embodied energy and associated CO₂ emissions. In addition, these bricks contain high recycled content and divert waste material from landfills.

The Problem – High Embodied Energy in Masonry Construction

Numerous organizations have shown that approximately half of the current energy consumption in the US (49%) is attributable to the built environment¹. About 22% of that energy is consumed by residential buildings and 17% is consumed by commercial buildings. Construction and building materials are responsible for the remaining 10% of built environment energy consumption. By comparison, transportation is responsible for about 28% of national energy consumption and industrial operations are responsible for about 23%.² Similarly, the built environment is responsible for 55% of the greenhouse gas (GHG) emissions in the US.³ Finding ways to reduce both energy use and GHG emissions has been the focus of green and sustainable design strategies in recent years and great strides have been made in some cases.

Image courtesy of CalStar Products, Inc.

Organizations such as the American Institute of Architects (AIA), Architecture 2030, and the US Green Building Council (USGBC) have all promoted significant reductions in the use of fossil fuels in buildings. For example, Architecture 2030 initiated the 2030 Challenge, which has since been endorsed by many other organizations. The 2030 challenge calls for "a measured and achievable strategy to dramatically reduce global building sector energy consumption and GHG emissions by the year 2030." It proposes that all new buildings, developments and major renovations reduce fossil fuel use, greenhouse gas emissions, and energy consumption by 60% compared to the regional average for that building type in 2010. Subsequently, every 5 years, the targeted fossil fuel use moves down 10%, so that by 2015, buildings should be at a 70% reduction compared to baseline averages; by 2020 an 80% reduction; and by 2030, all buildings will be carbon-neutral, using no fossil fuels to operate and thus emitting no GHGs during operation.⁴

The Architecture 2030 group envisions this targeted goal will be implemented via innovative sustainable design strategies such as conservation, improved building design, and on-site renewable power, as well as limited purchased renewable energy. Change is clearly underway: according to the Energy Information Administration's 2011 Annual Energy Outlook (AEO), estimates of residential and commercial building energy use to 2030 have been dropping dramatically since 2005 – by nearly 70% – due primarily to building design and increased building efficiency.⁵ Architecture 2030 has cited this on their website, (www.architecture2030.org) noting that "the AEO 2011 projects that the average Primary Energy Use Intensity of the Building Sector will continue to decrease and, in the best available technology case, begin to approach the goal of the 2030 Challenge." This is excellent news and a great plan, but focuses only on the operations of the building and not necessarily on the construction or the embodied energy to create the building materials.

As a follow up to this initial challenge, Architecture 2030 issued the 2030 Challenge for Products, in February 2011. This program parallels the Architecture 2030 Challenge, but is aimed at reducing the embodied GHG emissions of building products rather than buildings themselves. It calls on the global architecture, planning, design, and building community to adopt and implement specific targets for building products similar to the targets for buildings overall. Specifically, it calls for products in new buildings, developments, and renovations to be immediately specified to have a 30% reduction in carbon footprint, as compared with the product average. By the year 2015, that reduction shall be reduced to 35% or better, with increasing reductions to 40% by 2020, 45% by 2025, and 50% by 2030.⁶ Since the embodied energy necessary for many building materials and the associated greenhouse gases emitted in their manufacturing process is so high, those of us who design buildings and specify materials must also consider this important segment of energy consumption.

The National Institute for Standards and Technology's (NIST) Building for Environmental and Economic Sustainability (BEES) Database 4.0 tracks the total US energy consumption and emissions of common building materials. (See Figure 1) Among the biggest consumers of energy, and consequently, large contributors of CO₂ emissions, are cement and concrete products, gypsum board and clay brick products. Consider the materials used for a typical sized American home. A typical foundation uses 80 cubic yards of concrete, which requires 19 tons of Portland cement.⁷ The manufacturing of Portland cement is documented by the BEES database to be one of the largest sources of GHG emissions. One pound of Portland cement creates about 1 pound of CO₂ emissions during production. This means that our typical home with 19 tons of Portland cement accounts for about 19 tons of CO₂ in just the concrete alone, and that's before we get to any other materials.

FIGURE 1: Annual embodied energy and CO2 emissions from common building products. Source: NIST BEES database. Image courtesy of CalStar Products, Inc.

The production of clay brick is also responsible for large amounts of greenhouse gases, primarily due to firing the brick in a kiln at approximately 2,000 degrees Fahrenheit for several days. On average, 6,000 BTU of energy are used to fire each clay brick and nearly a pound of CO₂ per brick is emitted during that process.⁸ For example, if we look at an example project of a small multi-tenant condo building that uses a relatively small quantity of 20,000 clay bricks, we see that the bricks in this building are responsible for 120 million BTU's and 18,000 pounds of CO₂ emissions. For comparison, this is the amount of energy needed to operate a single-family home for about a year. The CO₂ emissions are equivalent to those emitted by a car for more than a year and a half.

How best to address this problem? In the 30 years between 2005 and 2035, the U.S. Energy Information Agency forecasts that the US will demolish about 50 billion square feet of space, remodel 150 billion square feet, and build another 150 billion square feet.⁹ All in all, by 2035, the EIA projects about 400 billion square feet of total space, three-quarters of which will have either been remodeled or built new between now and then. Thus, there is a substantial opportunity to transform our built environment to be more energy efficient – including embodied energy in the materials we use.

The Clay Masonry Industry Response

Clay masonry production has several major environmental impacts, including raw material extraction, energy consumption, and CO₂ emissions. First, in mining the raw material of clay and shale, the immediate consequences include the incident removal of plants, grasses, vegetation, and topsoil. The land is often properly restored, but when it is not, the condition of the mined area can be detrimental to the immediate and surrounding area. Second, with respect to energy consumption, an average of 6,000 BTUs of fossil fuels per brick are consumed during manufacture depending on the brick and the efficiency of the plant operations.¹⁰ Finally, in terms of CO₂ emissions, the combustion of the fossil fuels directly emits greenhouse gases, which are released into the atmosphere.

Recognizing these issues, there is some movement within the masonry industry to reduce embodied energy and move toward the goals of the 2030 Challenge for Products. In an effort to offset material use, reduce energy consumption, and lower costs and CO₂ emissions the clay brick industry has implemented or investigated the following options. (See Figure 2)

• Reduced material usage: Currently a clay brick is considered "solid" if 25% or less of the volume is cored or void space. Some bricks have voids greater than 25%, which lighten the unit and require less clay material and less fuel per brick. This also can allow more units to be shipped on a truck making transportation more efficient.
• Alternative fuels: A few U.S. clay brick plants use methane gas that is formed from decomposing trash in a landfill as an alternative energy source. These plants pipe the methane from the landfill to their kilns. If the landfill methane is insufficient to fire the kilns alone, it can be blended with traditional fossil fuels such as natural gas. Some plants burn petroleum coke, which is a by-product of refining oil and can be less expensive than coal or natural gas. While petroleum coke is considered a recycled fuel, it produces more greenhouse gas emissions than other fossil fuels.
• Alternative materials: Some manufacturers are using supplemental materials in addition to clay to reduce the impacts of their products. For example, some are using recycled glass, ceramics, and even processed sewage waste as an additive to the clay. In all of these cases, however, the brick is still fired, which means that the clay material extraction is reduced somewhat but the energy and emission impacts do not necessarily decrease because the firing remains the same. In terms of looking at entirely new materials rather than clay, one can consider concrete brick. Since concrete bricks are not fired, they have less embodied energy. But concrete brick contain about 15% Portland cement—a carbon-intensive material—so the concrete brick greenhouse gas emissions end up being about the same as clay brick.

FIGURE 2: Typical production strategies and results of clay brick manufacturers related to raw material, energy and CO2 emissions. Image courtesy of CalStar Products, Inc.

When one looks at all of the current initiatives just discussed, it is clear that the clay brick industry is achieving some limited success in raw material (clay) reduction. However, there is generally not much impact on the total energy used or CO₂ emissions generated, depending on the strategy employed.

Fly Ash Brick– A New Sustainable Option

From the previous discussion, we can see that the current clay masonry industry has many obstacles in meeting the 2030 Building Products Challenge. However, a new, innovative technology has emerged that produces masonry in a more sustainable way. This technology eliminates the use of clay, energy-intensive firing, and CO₂-intensive Portland cement completely and instead uses recycled fly ash as the binder. These low-energy, low-CO₂ masonry units meet the same testing criteria as clay and concrete and perform the same as traditional clay and concrete masonry.

When coal is burned in electric power plants to produce electricity about 5-10% of it turns into fly ash and remains behind. Fly ash is an extremely fine, lightweight powder, captured in filters before it can escape into the air. According to the American Coal Ash Association, the majority (55%) of the 72 million tons of fly ash produced annually is disposed of,¹¹ typically in landfills, though older plants can use surface ponds, which can create significant disposal issues. In some cases, there have been environmental problems with disposal in facilities not practicing best management techniques. This has caused the US Environmental Protection Agency (EPA) to consider regulating fly ash disposal, to allow for a national guideline rather than the current, non-uniform regulation that occurs at the state level.

About 45% of fly ash is diverted from landfills through beneficial reuse (recycling) in a variety of applications, including building materials and products. The EPA's regulatory focus is only on disposal. Recycling fly ash remains free of regulation, and, in fact, is encouraged by many organizations with different stakeholders. The US EPA, the Natural Resources Defense Council (NRDC), Earthjustice, and the U.S. Green Building Council have all agreed that recycling fly ash in building materials and products is beneficial and environmentally desirable. Hence, the EPA and leading environmental groups would like to see this beneficial reuse grow. Some of the reasons for this include the following:

• Coal use: Even as alternatives become available, it is clear that we're going to be living with coal-fired power plants for some time, whether the byproducts are recycled or not. Beneficial reuse in building products is preferred and endorsed by a broad group of environmental organizations because it is a superior alternative to disposal in landfills or ponds.
• History: Fly ash has been included in projects dating back to the Hoover Dam in the 1930's. It is an effective supplementary cementitious material and commonly replaces 15-20% of the cement in an average concrete mix today. Notably, the EPA headquarters building contains fly ash in the concrete.
• Recycling: The beneficial reuse of fly ash is one of the most compelling recycling success stories on record. For every ton of cement replaced by fly ash, we eliminate about a ton of CO₂. This practice has reduced U.S. CO₂ emissions by over 200 million tons since 1990.
• End of product life disposal: When fly ash is incorporated into a building product like concrete or bricks, it is tightly bound. Numerous tests on building materials and products conducted by the EPA and others have shown no concern for disposal of building products containing fly ash.

Frances Beinecke, President of the Natural Resources Defense Council (NRDC), recently wrote a book titled Clean Energy, Common Sense where, in chapter 5, she talks about a new brick company in Wisconsin making brick from coal fly ash. She notes that the finished product has 85% less embodied energy and 85% fewer greenhouse gas emissions compared to incumbent clay brick products.¹² This reduction means that this manufacturer has already exceeded the 2030 Product Challenge goal of 50% "embodied carbon" reduction by the year 2030. A comparison of the manufacturing processes of both clay bricks and fly ash bricks reveals how this result is achieved. (See Figure 3)

In the clay brick manufacturing system, clay and shale are mined and delivered to the plant where grinding and screening occurs. Water and additives are then added and mixed with the clay and shale. The resulting wet clay material is extruded into brick shapes that are dried to remove excess moisture. Once appropriately dried, they enter the kiln where they are fired at 2,000 degrees Fahrenheit for several days, which consumes the large amounts of energy already discussed. Once removed from the kiln, the bricks are then cooled slowly before being packaged and shipped to the market.

FIGURE 3: Traditional clay brick manufacturing compared to fly ash brick manufacturing processes resulting in 40% recycled content and 85% energy reduction. Image courtesy of CalStar Products, Inc.

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."

LEED & Beyond – Designing with Fly Ash Brick

The U.S. Green Building Council considers fly ash to be a post-industrial recycled material, which can contribute to LEED points for recycled materials (Credit MR 4 under LEED 2009). This is just one way in which fly ash unit masonry can contribute to green and sustainable buildings. Other ways include the following:

• Sustainable Sites: (See Figure 6)
• Alternative Transportation – Public Transportation Access: Fly ash pavers can be used effectively for biking or pedestrian paths between buildings and transit stops.
• Stormwater Design – Quantity and Quality Control: If used in pervious paving areas, fly ash pavers can contribute to an effective stormwater design solution helping to control both the quantity and quality of that stormwater.
• Heat Island Effect – Non-roof /cool paving: High-reflectance fly ash pavers or open-grid pavement will perform quite well as an alternative to dark, heat absorbing pavement.
• Heat Island Effect – covered parking: If used on the roof of a covered parking structure, fly ash pavers that are reflective will reduce the heat island effect.
• Water Efficiency:
• Water-Efficient Landscaping: If used as part of a pervious paving area, fly ash pavers can be used in the overall landscaping plan and its corresponding water efficiency.
• Energy and Atmosphere:
• Optimize Energy Performance: The thermal mass of fly ash bricks can be used to help control temperature fluctuations and truly optimize building envelope performance.
• Materials and Resources:
• Recycled Content: Fly ash masonry products typically contain 40% post-industrial recycled content.
• Regional Materials: For sites within 500 miles of factories, fly ash bricks and pavers help reduce the energy used in transporting materials.
• Indoor Environmental Quality:
• Thermal Comfort – Design: The thermal mass of fly ash bricks can help maintain comfortable interior temperatures with fewer fluctuations.
• Enhanced Acoustical Performance, Schools: Brick can help reduce transmission of background noise into core learning spaces due to its high density as a material.
• Innovation:
• Other possibilities for innovative uses of fly ash brick in buildings exist particularly related to life cycle improvements. For example, fly ash is often used to replace part of the Portland cement in concrete, which reduces the overall lifecycle impacts of concrete, by reducing the associated embodied energy and CO₂. A similar case could be made for fly ash brick replacing clay brick and reducing the overall embodied energy and CO₂ of the brick.

FIGURE 6: Fly ash pavers can contribute to a variety of sustainable site initiatives in addition to other energy and environmental benefits. Image courtesy of CalStar Products, Inc.

Beyond building construction and operations, using a comprehensive design strategy to incorporate materials with reduced embodied energy and carbon footprints is clearly the way to reduce the impact of building materials on the environment, as well as achieve the goals of other programs such as the Architecture 2030 Challenge for Building Products.

Conclusion – Sustainable Bricks of the Past, Present, and Future

If we look at a timeline from the beginnings of brick masonry through the present, it is interesting to note that we might be coming full circle. (See Figure 7) The Ziggurat in Iraq, built in 4000 BC, was constructed of sun-dried brick that required no kiln firing thus consuming no fuel and creating no CO₂ emissions, yet produced a brick durable enough to last through to present times. The Monadnock building, built in Chicago in the late 1800's, used 6-foot thick solid masonry walls at the base. Highly inefficient vertical brick kilns consumed massive amounts of fuel, about 30,000 BTUs per brick, and consequently emitted large quantities of greenhouse gas emissions in the process. The Exeter Library in New Hampshire designed by Louis Kahn and built around 1970 benefited from some improvements in clay brick making, which lowered the fuel consumed in firing down to about 8,800 BTUs per brick, or the typical range of current tunnel style brick kilns. If we look at current projects, it is possible that if new fly ash brick making technology were used, the fuel consumption and greenhouse gas emissions could be reduced to levels closer to the construction of the Ziggurat. Through this innovative thinking and fly ash-based technology, brick masonry really can come full circle to provide timeless character while offering the sustainability qualities that our planet demands.

FIGURE 7: The historical progression of brick technology and the resulting energy and CO2 emissions. Image courtesy of CalStar Products, Inc.

Peter J. Arsenault, FAIA, NCARB, LEED-AP is a practicing architect, sustainability consultant, and free-lance writer focused on work related to design, sustainability, and technology solutions nationwide. He can be reached at www.linkedin.com/in/pjaarch

ENDNOTES
1	Energy Information Administration, 2011
2	Energy Information Administration
3	“Potential Carbon Emissions Reductions In the Building Sector by 2030”, Brown, Stovall & Hughes, Oak Ridge National Lab
4	www.Architecture2030.org
5	Energy Information Administration Annual Energy Output (AEO) 2005, 2007, 2009, 2011
6	See Architecture 2030
7	NAHB, 2004 Housing Facts, Figures and Trends, Feb. 2004, p. 7
8	NIST’s BEES 4.0 database reports 8800 BTU per modular brick equivalent. The BIA reports 1240 BTU/lb or 5200 BTU per modular brick equivalent. A middle figure of 6000 BTU per modular brick equivalent was chosen for these calculations.
9	Architecture 2030; Data Source US Energy Information Administration
10	Ibid viii
11	ACAA annual production surveys
12	Frances Beinecke, President of National Resources Defense Council, CLEAN ENERGY, COMMON SENSE; Chapter 5

CalStar Products has reinvented masonry to make it more sustainable and more affordable. Our masonry products represent a significant improvement in environmental performance over fired clay and concrete products including 40% recycled content, 85% smaller carbon footprint and up to 85% less embodied energy. www.calstarproducts.com