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.