Making Strides

Cement manufacturers join the green movement and strive to make their products more environmentally friendly.

By Bridget McCrea

Sustainability hasn’t come easy for the cement industry, but that doesn’t mean attempts aren’t being made to create “greener” options for this critical, base material. A powdery substance made by calcining lime and clay, mixed with water to form mortar or mixed with sand, gravel and water to make concrete, cement’s environmentally friendly properties aren’t always easy to identify.

But that doesn’t mean the industry is sitting on its hands while the rest of the world attempts to minimize its carbon footprint (the total set of greenhouse gas emissions caused by an organization, event, product or person). David Shepherd, director of sustainable development at the Portland Cement Association in Skokie, Ill., admits that whittling down cement’s carbon footprint hasn’t been easy.

While nearly every building material has an environmental impact, the energy-intensive nature of cement’s manufacturing process makes it a particularly tough nut to crack. Shepherd compares cement with steel, the latter of which “has a larger carbon footprint than we do,” he says. “For (cement), it comes down to the actual manufacturing process and the formulations that are being used.”

Location also makes a difference. In Europe, for example, cements are blended with other materials to create greener products, thus enhancing the environmentally friendly aspects of about 65% of the total cement purchased. In the United States, however, Shepherd says pure portland cement is in the highest demand, with blended mixtures comprising only about 5% of total cement production.

That’s where Shepherd’s two-person department comes in: to help spread the good word to specifiers, engineers and architects about the value, strength and limitations of blended options. Unfortunately, breaking through those age-old barriers can be challenging, especially when it comes to getting cement manufacturers to build new silos or make other changes to accommodate new processes and formulas.

“There are logistical aspects to consider, such as how you store the (blended) cement, and what additional structures and equipment have to be added to the plant,” says Shepherd. “All of these things need to be addressed.”

By the numbers
Pound for pound, concrete has a low embodied energy. But since it’s used in all facets of the modern world, there are “a lot of pounds being made,” says Shepherd. Each year, more concrete is used than wood, steel, plastic and aluminum combined, according to the World Business Council on Sustainable Development. “Concrete’s strength, durability and local availability make it a valued commodity for buildings and infrastructures alike,” he says.

Standing behind (or rather, mixed in with) those pounds of concrete is a substance that has taken a bad rap for its “non-green” qualities, but Shepherd says the cement industry is making strides in reversing that reputation. Since 1972, PCA members have reduced the energy consumption required to make a ton of product by 37%, he points out, and members have voluntarily committed to a 20% energy reduction (from a 1990 baseline) by 2020.

“The U.S. cement industry has adopted a year 2020 voluntary target of reducing CO₂ emissions by 10% per ton of cementitious product produced or sold,” says Shepherd.

Here are a few more points about how alternative fuels and raw materials are being used in the cement-making process:

• 10% of energy consumption in 2008 was via waste fuels (tires, waste oil, unrecyclable plastics, etc.)
• 50 (of 115 U.S. plants) used fly ash
  and bottom ash as raw material feed
  in 2008
• The concrete industry used 20 million tons of recycled industrial byproducts in 2006.

Shepherd says such headway is being made with one simple goal in mind: to reduce the size of the industry’s carbon footprint – much like every other industry across the globe that is either being forced to do the same or tackling it voluntarily.

“We’re seeing an environmental movement in everything from car manufacturing to packaging to everyday consumer goods,” he says. “The (movement) is receiving various levels of support from industry, government and consumers. Clearly the trend is expansion rather than contraction, it does not appear to be a fad.”

Fostering sustainability
Creating materials that are used to develop sustainable construction projects is an important mission for Lafarge North America Inc., according to Kevin Cail, the Reston, Va.-based firm’s director of sustainability and commercial innovation. Key points that are perpetually under consideration, for example, include the products’ energy efficiency, durability and longevity.

Resiliency also comes into play. “We look closely at how our products can be used to withstand severe climates, and natural disasters like earthquakes and tornadoes,” Cail explains. “These are issues that weren’t even thought about 10 years ago. Today, I don’t think there’s an architect out there who doesn’t look at these (factors) when designing buildings.”

When tracing those buildings back to the plants that make the cement that goes into the raw construction materials, there are some foundational components and processes that make environmentalists cringe. “Cement is a smokestack industry that produces a lot of CO₂ per ton of material,” says Cail, who estimates that historically the industry has produced about one-eighth of a ton of CO₂ per ton of product made (depending on the individual plant’s technology and efficiency).

That CO₂ hails from two different areas: the decarbonation of the limestone itself, and the fuels that are used in the kiln during the clinkering process (clinker is the intermediate product that is produced by heating in the kiln). “We use a lot of fuels (including coal and fossil-based), and most of them have been traditionally carbon-based,” Cail explains.

Cail says Lafarge has been working over the past 10 years on a multifaceted approach to reduce fuel consumption and, in turn, the amount of CO₂ flowing out of the manufacturer’s smoke stacks. A primary focus, for example, has been the use of alternate fuels in lieu of traditional, carbon-based options. “The industry in general, and our company specifically, have been actively working to use these alternate fuels,” says Cail.

Attention is also being paid to the limestone decarbonization process, although Cail points out that because this is a chemical process, “there’s not a lot that can be done.” However, he says, it is feasible to replace the limestone with alternate raw materials that will positively impact the overall CO₂ footprint. A final step, says Cail, involves reducing the amount of clinker used per ton of CO₂.

“If you can use less clinker per ton of cement, then you directly affect the amount of CO₂ per ton of cement,” says Cail. “There’s been quite a bit of focus on this effort across the industry and here at Lafarge, where we’re producing blended cements.” Those alternatives (which Shepherd discussed earlier in this article) use less clinker per ton, as they rely on raw materials like slag and fly ashes, “and still produce essentially equivalent performance to regular portland cements,” says Cail.

Breakthrough developments
One of the biggest breakthroughs in the cement industry’s attempt to create more sustainable practices has been the incorporation of limestone into the cement itself. “This isn’t about adding limestone into the kiln that gets decarbonated,” says Cail. “It’s about putting limestone directly with the clinker in the grinding process, which reduces the amount of clinker used.”

This process, and the technology behind it, has been used in Europe for years, says Cail, and is now making it’s way to North America. Traditionally, he explains, cements in the United States and Canada have allowed for a maximum of 5% limestone. The Canadian specification has been changed to allow up to 15% limestone, which results in 10% less clinker per ton of cement (and thus a 10% reduction in CO₂ emissions).

“Having the specifications that allow the use of up to 15% limestone has a fairly significant impact on CO₂ (emissions),” says Cail. While the U.S. standards remain at 5%, he says that both cement specification regulatory bodies (ASHHTO and ASTM) are working to create new specifications that would match those currently being used in Canada. “There is clearly a move afoot at these organizations to get those specifications changed,” Cail adds.

Finding alternatives
Individual companies are also making strides when it comes to finding ways to manufacture strong, sustainable products at a lower environmental cost. At CERATECH in Alexandria, Va., for example, the company utilizes about 94% recycled waste coal ash to make ekkomaxx, a trademarked alternative to traditional portland cement technology.

Using a single powder system comprised of various proprietary activators, the manufacturer produces cement from 100% reclaimed, green sustainable materials. “We use materials that were going to the landfill, throw in our activator and create a high-performance cement that looks and acts just like portland cement,” says Leo Kahl, vice president of marketing.

Kahl says Gainey’s Concrete Products in Holden, La., is one of the first NPCA producer members to integrate CERATECH’s technology into its manhole products. One of the most attractive qualities of the alternative product is the fact that it is microbial-infused, which repels the chlorides that attack precast wastewater piping, he explains.

While traditional portland cement remains the base material of choice for many concrete manufacturers, Kahl envisions a time when more alternative products become available, and more readily used.

Greener pastures
With sustainability permeating every corner of the business world, expect to see portland cement manufacturers taking more steps to reduce their carbon footprints. The efforts make perfect sense, according to Shepherd, who points out that there are environmental, societal and economical benefits to moving in that direction. With energy expenses heavily impacting cement manufacturers’ bottom lines, for example, Shepherd says basic steps like reducing energy consumption is a no-brainer.

Due to the sheer size of the cement plants, and the systems that run them, making those strides does take time. “These plants are extremely large and capital intensive,” Cail points out, “so change and improvements don’t happen all in one big leap.”

But as new plants come on line, and as older ones are phased out, the move to become environmentally conscious does occur within an industry that’s received some harsh criticism for not getting on board with the green movement fast enough. “When you take out the weak links and replace them with state-of-the-art options, the numbers (reflecting the volume of CO₂ emissions, for example) go down,” says Cail. “There’s been good momentum so far, and we expect that to continue.”

Bridget McCrea is a freelance writer who covers manufacturing, industry and technology. She is a winner of the Florida Magazine Association’s Gold Award for best trade/technical feature statewide.