Green Piece-Reducing Cement’s Footprint

By Kyle Kerstiens, Assoc. AIA, LEED AP

Concrete is second only to water as the most used substance in the world. Because of this need for concrete, cement, which serves as the glue, is also produced in large volumes. This massive demand, along with the heat required to produce it, is why 5% of global CO₂ emissions is attributed to the cement industry. Even though concrete is seen as an important and necessary product – and with consumption seemingly ever on the rise – the cement industry has been working for many years to reduce that carbon impact in order to be competitive in the construction industry and to become better stewards of the environment.

In order to effectively transform the carbon impact, 10 of the world’s largest cement manufacturers formed the Cement Sustainability Initiative (CSI) in 1999. That number has since ballooned to more than 23 cement manufacturers that collectively account for about one-third of the world’s cement manufacturers and more than one-third of the world’s cement production. Their goal is to set up a framework of objectives on the road to sustainability.

As part of that path, the CSI produced a Concrete Technology Roadmap in 2009 outlining its carbon emission reduction strategies leading up to the year 2050.

Application
A number of low-carbon, carbon-neutral and even carbon-negative cements have been introduced to the market over the past few years. Because these new technologies are still in their infancy, the cement industry first needs to improve the systems already in place. Four key areas that would alter the carbon footprint most effectively are:

• Thermal and electric efficiency
• Alternative fuel use
• Clinker substitution
• Carbon capture and storage

Thermal and electrical efficiency
New technologies are always emerging in any industry, and that includes cement production. New kilns are much more energy efficient than their predecessors, but they have an inherently high retrofit investment cost. It will take the industry some time to phase out old equipment, but as new technologies become more efficient, it should in theory help cement manufacturers make the choice to invest in new technology.

Alternative fuel use
According to CSI, conventional fuels like coal still make up about 90% of cement manufacturing’s usage. Alternative fuels such as discarded tires, waste oil products, biomass, plastics, textiles and paper can all help replace the use of coal, which will also reduce the overall carbon footprint of cement and concrete.

These alternative fuels come with their own limitations. Pretreatment often is required, because the different products burn at varying rates, have different moisture levels and emit different chemicals that affect clinker production and fossil fuel usage.

The low 10% alternative fuel usage rate in the United States can also increase with waste management legislation. As proper waste management continues to develop, landfilling these types of products without consideration will diminish, and the alternative fuel percentages should climb higher toward some of the 50% levels seen in some European countries

Clinker substitution
Blast furnace slag, a byproduct of the steel industry, and fly ash, a residue from coal-burning power plants, can be used in larger percentages to partially substitute clinker. Local availability, prices, standards and properties of these SCMs are all factors that have limited the use of higher batch percentages. One example is pending environmental regulation of fly ash, which has been closely monitored in the industry of late. It is widely accepted that as popularity of SCMs increase with contractors, engineers and customers, these factors will become less important. All concrete-related industries are working hard to market the acceptance of larger quantities of substitution through better education, although acceptance typically relies more heavily on laboratory testing and proven performance in the field.

Carbon capture and storage
Carbon capturing is a relatively new technology with its first underground storage in 2000. The fundamental problem with carbon capturing for either storage or future scrubbing is the cost of additional fossil fuels to separate the CO₂. Some estimate that cost to be from 20 to 45% more fossil fuel to accomplish proper CO₂ storage.

Essentially CO₂ is captured as it’s released in the burning process and compressed to a liquid form. It is pumped deep underground, often used in depleted gas and oil wells. One of the newest ways CO₂ is being utilized is in enhanced oil recovery, in which the CO₂ is simply pumped into an oil field in order to increase the yield of crude oil.

Business benefit
With the cement industry working to improve its sustainability record, the precast industry can market itself more effectively. It cannot fight the general statement that cement accounts for 5% of global emissions without remaining cognizant on the facts. For example, compared with 1972, it now takes 37% less energy to produce a ton of cement – enough to power 2.3 million homes a year. There is also a strong case to be made for the 100-year-plus lifespan of most precast concrete products. That’s a sustainable argument in which precast products compare favorably with petroleum-based products such as plastics. It’s a strong start, and the cement industry has a solid plan in place to become more sustainable year after year.