Cement and Concrete: What’s the Difference? What Effects Do They Have on Sustainability?

There are some age-old questions out there:  What’s the difference between bourbon and whiskey?  A calzone and a stromboli?  A fiddle and a violin?  What about the difference between cement and concrete?

To keep it short and sweet, cement is a binding agent in powder form and is a component used for concrete, mortar, stucco, grout, and even some adhesives.  Once combined with water, cement will eventually set and harden.  The subsequent building material name depends on what is mixed with the cement.  For example, concrete is cement mixed with sand and gravel (or other mixture of fine/coarse aggregate) as a tried-and-true, complete building material.

OK – that’s a great start.  Cement is the “glue” that holds concrete together. Where does sustainability come in?  For that, we need to go into how cement is made.  Cement is made from a variety of feeds, with the most-common feed being limestone.  Other materials (such as sand, iron, aluminum, and clay) are added to the limestone, as needed, to ensure that the raw material contains the right components to become cement.  This material is then fed into a kiln and “baked” at around 2,700 degrees Fahrenheit.  After exiting the kiln, the material, now called clinker, is cooled, ground up, mixed with gypsum to regulate the time it takes the cement to set (and potentially other additives depending on the type of cement), and then packaged for use.  Its usefulness in construction makes it one of the most widely used materials in the world.

So what?  With hints to a massive infrastructure bill in the news, cement and its building material derivatives (including, but not limited to concrete) may have a significantly increased demand with a corresponding increase in production.  Cement production has its fair share of environmental challenges and cement plants must continue to monitor their effect on the surrounding environment.  With increased production due to the infrastructure bill, there may be more attention directed towards the environmental effects of cement production, not least of which are greenhouse gas (GHG) emissions.

Manufacturing cement produces a significant amount of carbon dioxide (CO₂) both through the process (limestone + heat -> calcium oxide and CO₂) and through the burning of fuel to maintain the high temperatures required in the cement kiln for the baking process.  Fossil fuels are the type of fuel most often utilized in kilns since a high temperature must be maintained, and fossil fuels are the most available and economically feasible fuel for such operations.  Due to the scale of production of cement, these sources contribute a significant portion of GHG emissions [e.g., according to U.S. EPA’s GHG Reporting Program for large-emitting facilities, the cement industry accounted for 58% of the CO₂ equivalent (CO₂e) emissions in the U.S. minerals sector, and 2.4% of total U.S. CO2e emissions in 2019].

Therefore, there is some pressure on the cement industry to mitigate GHG emissions through a sustainable reduction in GHG emissions, primarily CO₂.  CO₂ emissions can potentially be reduced from an operational standpoint in several ways: by increasing the efficiency of production (less energy spent to create the same amount of clinker), replacing clinker with an alternative material or filler (less clinker required to make the same amount of cement), and by using alternative and/or waste fuels to reduce CO₂ emissions from kiln combustion.  Of course, reducing CO₂ emissions in these ways comes with their own set of disadvantages (e.g., a potential drop in cement quality or installation of expensive equipment), but are good approaches to reduce CO₂ emissions from cement kilns.

In addition to sustainable reductions in GHG emissions from process changes, post-combustion GHG emissions controls continue to be evaluated.  In the cement industry, however, there are several technical issues that prevent the current control technologies from being implemented on a wide scale (e.g., high temperatures, excess material in the exhaust gas, and continuous wear and tear of the control equipment).  Developing a reasonably affordable and technically feasible post-combustion GHG emissions control technology for widespread use in the cement industry will take time to complete.

ALL4 will continue to track both the pressure of sustainability on the cement industry as well as the development of CO₂ control technologies for sustainable cement production.  If you have any questions, please contact me at scunningham@all4inc.com or (610) 422-1144.