Author: Sydney Smeets
ABSTRACT: Concrete is the most universally used building material that defines urban infrastructure. The chemical process to create cement and other ingredients that form this artificial rock are highly carbon intensive. It is only through rethinking this material, its chemical properties, and our reliance on it that the building industry can lower its carbon footprint.
Cement, Concrete, and Carbon go hand in hand. The three unfortunate C’s that relate so closely in their prominence together.
Concrete is the most universally prevalent building material. Due to the abundance of the ingredients that comprise cement, it can be made almost anywhere without imports.
Cement is the component or “ingredient” within concrete that makes concrete what it is, an artificial rock. The mixture of cement with water “hardens and binds the aggregates into an impenetrable rock-like mass” known as concrete (Howden, 2021). Cement is comprised of Lime (calcium oxide), Silica (silicon dioxide), Alumina (aluminum oxide), Magnesia (magnesium oxide), Sulfur Trioxide, Alkaline, Iron Oxide and Calcium Sulfate through chemical means. All of which are then extracted from earthen materials including limestone, clay, chalk, sand, shale, bauxite, and iron ore; limestone and clay being the most prominent and historically used extraction material in building construction of this kind. What makes these natural resources become artificial materials is the chemical reactions that occur in creating a new, irreversible state.
The process begins with making the cement. The ingredients are extracted from quarries. The raw materials are transported to “crushing installations” where they are then “crushed” and “broken down to…the size used in road metaling” (Heidelberg Cement). The material is homogenized and crushed in various series until it is a powder. Along the process other components are mixed in to create the desired type of cement. The powder mixture is then burned at a temperature over 1400°C. This is the chemical process that bonds and turns the mixture into an artificial product, clinker. After all ingredients are added, they are shipped to the desired location to mix with water and aggregates on site, making concrete as the final product.
We see concrete everywhere. The application of concrete defines our infrastructure of cities and suburban areas. Concrete is a major component in buildings, bridges, roads, and dams among other applications. The earliest examples of concrete like buildings include the technique that used adobe or “mud brick” similar to that of cob or rammed earth buildings. All of which are still very viable methods and created buildings that last for thousands of years evidenced in the “famous city of Shibam in Yemen (King, 2018, p.71).” Before the mixture of cement we know today was established in the industry, clay was the binder used in these methods. Silt is in a similar family to clay but because of its larger particles, cannot be used as effectively, so clay was the binder of choice. Today Portland cement is the most commonly used form of cement, being a combination of cement, sand and gravel to different percentages, despite the many other options that include limestone and clay among others.
Consistently, similar statistics of cements’ carbon impact have been found. The most widely discussed being that “cement production today accounts for about six percent of all anthropogenic global emissions” denounced by Bruce King, author of the New Carbon Architecture (King, 2018, p.69). This being from the chemically laborious process of making the cement. “For every ton of Portland cement produced…a ton or more of carbon” is put into the air (King, 2018, p.69). The other issue, not addressed as widely, is that the demand is drastically outweighing the supply of concrete as a material and will continue to with current population growth. The infrastructure to support them is currently dominated by concrete production. The material shortage of all the ingredients that comprise cement is a problem that industries are now having to import to satisfy the demands. This adds to the emissions from transportation and carbon emissions associated with the shortages.
Due to the many variables and customizations within the composition of cement and concrete, a defined statistic of the embodied and operational carbon is just not realistic to know. There is no set number to define the specifics as each scenario presents its own individuality. The lack or addition of ingredients, reinforced concrete, various aggregates, and scales all influence. However, Environmental Product Declarations (EPD’s) give a better picture of the average global warming potential (GWP) – a rather outdated term but not to be addressed now – for the typical mixes and types of concrete, cement, and cementitious materials present. The only downside is that the “EPD’s for cement usually only quote the GWP for the ‘cradle to gate’” rather than cradle to grave (Anderson & Moncaster, 2020, Sec. 2). Even if the clinker content or ingredients were changed out or modified, the sheer quantity of its use in the industry becomes the larger issue. Our reliance on it in combination with the manufacturing chemical process to create the artificial material creates a dire combination of carbon emission trails.
In addition to the embodied carbon of the cement and concrete itself and the operational carbon of the buildings; the roads and bridges enable the reinforcement of cars as the easiest, largest, and most convenient transportation method. Although the carbon emissions from cars is typically considered an individual emission, the infrastructure of our urban and suburban centers is defined by concretes’ prevalence in enabling the easiest decision for consumers.
Currently, efforts are being made to utilize other ingredients and methods in cement production to satisfy the demand for the near future and create a more sustainable building material to meet the Paris 1.5-degree goal. The most resources are going into reducing – currently most carbon intensive part of the process – the production of clinker. Pozzolans are a more well-known clinker substitute. Considering they utilize waste products in this industry, this category of substitutes can aid in lowering the embodied carbon of concrete (King, 2018, p.78). Additionally, resources are going into the scalability of more historic methods like rammed earth structures and the use of clay, adobe, and cob. The difficulty then comes from the expansion of all these efforts to an industry that relies almost entirely on the use of concrete.
Efforts are also being conducted to not only reduce the amount and therefore impact of the concrete currently being used, but to look into methods of carbon sequestering in concrete, to reduce the amount of output from the industry, and to pull carbon out of the atmosphere into the aggregates being used. These methods are in their infancy, but the research and experimentation being conducted is quite inspiring.
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Sydney Smeets is a fourth-year student of Interior Design at Ryerson University. She has studied abroad at Middlesex University and is set to begin a graduate certificate in Environmental Visual Communications in 2021 after receiving her BID. She has grown up fascinated by environmental studies and hopes to learn more about sustainable design practices and inspire others to do the same.