Anita Brown: Cement Industry Emissions

Cement industry accounts for 5-7% of anthropogenic carbon dioxide emissions.[1] Cement is the main ingredient in concrete that gives the concrete its binding properties. Concrete is second to water in total volumes consumed by society.[2] The quantities of greenhouse gases emitted are a result of the large number of construction projects occurring, not necessarily the construction practices.[3] More than 5 billion tons of concrete are poured per year worldwide.[4] Concrete demand will continue to increase as countries develop and construction continues. Because concrete will continue to be the main building material used and cement will continue to be produced, the question becomes, how to effectively reduce the CO2 emissions in the cement industry. Before a proper recommendation can be made, a thorough examination needs to be made on the life cycle of concrete.

 

Cement Production

 

Cement is a powder made from calcareous deposits.[5] These raw materials provide calcium carbonate (CaCO3). The release of CO2 is a result of a process caused calcination, when the limestone is decomposed into lime. Calcination is a thermal treatment process in the absence of air or oxygen to cause thermal decomposition.[6] In this process, calcium carbonate (limestone) is decomposed into calcium oxide (CaO, lime) and carbon dioxide. The process occurs in a kiln by burning fossil fuels at temperatures of 1,450°C.[7] The decomposition of limestone emits 60-65% of the total emissions (the rest is generated by fuel combustion, which is mostly comes from heating the kiln). However, other materials, such as slag, fly ash, and limestone can be blended in to the product to decrease the amount of product that must go through the calcination process.

 

EPA Study

 

In 2009, the USEPA did a study on the potential for reducing greenhouse gas emissions in the construction sector. Most of their approaches were related to improving fuel efficiency and recycling material.[9] By recycling material approximately 1,400,000 metric tons of CO2e emissions can be avoided and the recycled material can be used as aggregates. The purpose of using aggregates in concrete is so that a smaller volume of cement would be needed in the mix. By reducing the amount of cement needed, less would be produced, and less carbon dioxide would be released as a result of cement production. However, there is a limit to the amount of aggregates that can be added before the strength of the concrete is affected.

Geopolymer Cement

 

Another possible solution to mitigate the carbon footprint of the cement industry is the use of geopolymer cements. Geopolymer cements are a material that combines aluminum silicate with an alkali chemical activator. Aluminum silicates can be found in industrial byproducts such as fly ash and blast furnace slag. Fly ash is a byproduct of coal combustion, and is mostly put in landfills where it is susceptible to leaching and spills. Using fly ash in cement would promote fly ash recycling and provide a way to reduce the demand for cement created through calcination. As mentioned previously, fly ash can also be used in the cement making process to decrease the amount of material that needs to go through the calcination process and produce carbon dioxide. Solely geopolymer cements have not been applied to large scale projects because of strength restrictions.

 

Cement Lifecycle

 

By studying the carbon footprint of concrete throughout its life, from the production of cement to the recycling of the material, it will be possible to see the true impact of the construction industry on the anthropogenic emissions. The impact of the lifecycle of cement is being studied by the Cement Sustainability Initiative (CSI).[13] Concrete structures can endure for centuries, with limited cost for maintenance and repair, and can be recycled into aggregates. Concrete also slowly absorbs CO2 from the air in a process called carbon sequestration or carbonation.[14] The amount of carbon dioxide sequestered in concrete is a significant percentage of the amount released during cement calcination.[15] Although cement productions is responsible for a significant percentage of carbon emissions within industries it is important to take this process into account.

 

Conclusion

 

In comparison to other building materials, the emissions from producing cement are relatively low. However, with the large volume of concrete being produced and in demand the total emissions from the cement industry are high. The best way to approach this problem would be the continued recycling of concrete and the use of substitutes within the cement, such as fly ash, that will decrease the total amount of cement that will need to be produced. Furthermore, the continued studying of the carbon footprint of concrete will allow for a better understanding of the carbonation of the concrete and how much carbon dioxide is being captured.

 

Eva Comment:  When I think of pollution, I tend to think of the usual suspects: vehicles, electricity companies, etc. I liked this post because it put into perspective the fact that, though they aren’t as prominent as some, there are other smaller contributors to carbon emissions. You did a great job of explaining what concrete has to do with carbon emissions: how the process pollutes the air, how much it contributes to carbon emissions, and what possible approaches to this are. Reading this makes me wonder if policymakers often consider creating legislation concerning smaller emitters like the concrete industry, or if they tend to only focus on industries with a larger impact/larger amounts of pollutants. Since it is often difficult to agree upon and pass legislation concerning large polluters, because their use is so widespread, perhaps it would be easier to take smaller steps with smaller emitters. At the same time though, concrete use is also widespread, so it could prove just as challenging to create agreed upon legislation for this. You’ve given what seem like good starting options for addressing concrete’s carbon emissions, and I would like to see if any of them are used in the future.

Noah Comment:

You do a very good job at outlining the problem of carbon dioxide emissions from concrete production and some potential solutions to the problem.  One of the things you mentioned was that the carbon dioxide that is emitted in the process of making concrete is from the burning of fossil fuels.  Every production process in the modern world uses some form of fossil fuels either directly or indirectly, whether through the use of electricity or in transportation.  Hence, concrete does not seem like a unique emitter of carbon dioxide but rather just a user of fossil fuels.  The solutions you propose, such as the recycling program, would very likely be helpful in reducing the amount of fossil fuels used in making concrete.  However, to me it seems the most direct and efficient way to reduce CO2 emissions from concrete would simply be a tax on coal and gas.  This would not only disincentivize the concrete industry from using fossil fuels but also other industries that do so.
If the government made special incentives for the concrete industry to reduce its fossil fuel use, it would also need to do the same thing with other industries.  It seems more direct to just implement an across the board tax on fossil fuels.

Nate Comment:

I think this was a great example of the unknown consequences of global development in relationship to climate change. I recently read a Forbes piece on China and their use of concrete; they have consumed more concrete in the last three years than United States has in the last hundred. Since it is unrealistic to assume that any international agency or nation could force developing nations to sizably reduce their concrete consumption, the international community should instead pledge to have a percentage of the total concrete they use come from a recycling process. Further more, developed and developing nations should pool their financial resources to fund research on more efficient ways to recycle and use concrete. I also think that urban planning plays a huge role in how concrete is used and its impact on the environment. More analysis needs to be done in large city centers to see how urban sprawl and inefficient real-estate development ( housing projects that don’t last as long as they are projected to) increase a cities carbon footprint.

Jennifer Comment:

This is a really interesting topic. I didn’t realize that cement industry emissions accounted for such a significant portion of greenhouse gas emissions. When I think of the environmental impacts of cement or concrete, I tend to think of the impacts of using them for paving in urban areas. Paved areas contribute to increased runoff, which tends to contain chemical and nutrient pollution. This runoff can cause a number of problems for nearby streams and wetlands including erosion and eutrophication. Cement paving also contributes to the Urban Heat Island phenomenon, which results in warmer temperatures and greater health risks to residents. These environmental and human health risks are justification enough for reducing the use of cement in urban areas, but this justification is increased when considered alongside the significant emissions from cement production. One potential change that could be implemented to reduce all of these environmental impacts would be the increased use of permeable pavements, which allow water to percolate down into the soil, thereby reducing runoff. There are different types of permeable pavements, but many use materials like clay instead of cement, or have cement interspersed with grassy areas. Both styles reduce the total amount of cement that would need to be used to pave areas, and the type with grass, would also help to cool urban areas through transpiration.  Increased use of permeable pavement could be used to address the underlying problem of high concrete consumption.

Randy Comment:

This is a very interesting topic that I did not know about prior to reading this post. I am interested in the alternatives to traditional cement fabrication that you mentioned. The use of recycled aggregates in concrete production to limit the need for cement seems like a good way to decrease the associated CO2 emissions. I feel like developed nations such as the United States should enforce this process which would ultimately lower the carbon footprint resulting from calcination process as well as provide an opportunity for fly ash recycling, which also has associated environmental risks. However, like you mentioned, there needs to be more research to develop stronger geopolymer cements before any sort of policy can be implemented. I would be interested to see the costs of geopolymer cement compared to traditional cement to see if any sort of national policy is economically feasible. As you mentioned, national and global concrete, and thus cement, demand will increase with development, so the large carbon emissions associated with concrete production is an important issue that needs to be addressed.

 

Jen comment:

Your analysis of the emissions associated with the cement industry is insightful and thorough. Like Eva, I tend to think of more ‘mainstream’ suspects when discussing pollution, so this was an interesting new perspective. Your post provides a great in-depth commentary on the drivers of the problem from which possible solutions can be created. This post made me think about our class discussion on Monday about the choice developing countries must make between progressing developmentally (thus encouraging more construction projects) and the need to decrease emissions. You mention that demand for new construction projects will increase and concrete will continue to be the primary building material used. Rather than focusing on reducing the carbon dioxide emissions in the cement industry, an alternative could be to focus on creating and producing a more eco-friendly, sustainable building material to take the place of cement/concrete. In your discussion of the EPA study, you mention the possibility of increasing the amount of aggregates in concrete to reduce the amount of cement needed. I’m curious as to whether the cement/construction industry has adopted any sort of regulations with respect to a baseline level of aggregate to be used in production, or what their stance is on adopting such practices. While this would likely be logistically challenging to implement, I think this would be the most effective way to initiate industry-wide best practices. Beyond this industry, Noah makes a very valid point regarding the greater flexibility that would come with an across-the-board tax on fossil fuels.

 

Colm comment:

I especially like your suggestion that governments adopt proactive approaches to deal with future water scarcity versus the reactionary regulation currently being implemented in California. While the current drought in California is incredibly unfortunate, it does provide the state and the country with a strong window of opportunity to create water regulations.

I think that metering water and differentiating between essential and non- essesential water use prices are policies that could be implemented nationally with great effect. Additionally, I think campaigns that promote sustainable water usage could be very effective. Pairing these two with reform to many of the greywater laws in states across the country, the federal government could be poised to enact regulations that seriously slash water consumption.

California’s current drought will not be the only one of this severity in the coming decades. Climate change will volatilize water availability, and I’ve heard people hypothesize that water will play a larger geopolitical role than oil within 30 years. This drought presents an opportunity for California and the federal government to create policies that will mitigate the severity of future droughts will also adopting more sustainable water management.

 

 

[1] USEPA, Potential for Reducing Greenhouse Gas Emissions in the Construction Sector. February 2009 (accessed February 2015); available from http://www.epa.gov/sectors/pdf/construction-sector-report.pdf

[2] Ibid.

[3] Ibid.

[4] http://urbaneden.uncc.edu/house/architecture/materials/geopolymer

[5] USEPA, Potential for Reducing Greenhouse Gas Emissions in the Construction Sector. February 2009 (accessed February 2015); available from http://www.epa.gov/sectors/pdf/construction-sector-report.pdf

[6] “Calcination”, Wikipedia. Last modified January 22, 2015. (accessed February 2015); available from http://en.wikipedia.org/wiki/Calcination

[7] USEPA, Potential for Reducing Greenhouse Gas Emissions in the Construction Sector. February 2009 (accessed February 2015); available from http://www.epa.gov/sectors/pdf/construction-sector-report.pdf

[8] “Calcination”, Wikipedia. Last modified January 22, 2015. (accessed February 2015); available from http://en.wikipedia.org/wiki/Calcination

[9] Geopolymer Cement Concrete. University of North Carolina Charlotte (accessed February 2015); available from http://urbaneden.uncc.edu/house/architecture/materials/geopolymer

[10] Ibid.

[11] Ibid.

[12] USEPA, Potential for Reducing Greenhouse Gas Emissions in the Construction Sector. February 2009 (accessed February 2015); available from http://www.epa.gov/sectors/pdf/construction-sector-report.pdf

[13] Ibid.

[14] Ibid.

[15] Haselbach, Liv, “Carbon Dioxide and Global Climate Change”, Portland Cement Association. (accessed February 2015); available from http://www.cement.org/for-concrete-books-learning/concrete-technology/concrete-design-production/concrete-as-a-carbon-sink

[16] Ibid.