Concrete and steel are unique substances that in some sense may be irreplaceable. After all, concrete ranks as the second most consumed substance on the planet, second only to water. Wherever you look, these materials are essential for roads, floors, buildings, bridges and so much more.
The History of Concrete and Steel
The initial use of concrete dates back to 6500BC, as residents of Syria and Jordan constructed their floors and cisterns. As time passed and global advancements were made, use for the material expanded. In 1891, George Bartholomew poured the first concrete street in the United States. Shortly after at the turn of the 20th century, another popular substance, steel, which had been used and improved since 2000BC, began to be integrated. Cement is the binder of concrete and only holds up to about 1% of its weight in steel. With steel-reinforced concrete however, resistance to both compression and tension forces decreased, which kept concrete from cracking. The usefulness for these two materials grew rapidly and proved to be integral in constructing a variety of things, including the first concrete high-rise in 1904 and the Hoover Dam in 1936. Famous steel buildings were also built, like the Empire State Building in 1931. Because these materials demonstrated reliability and were easy to create, mass production was all but guaranteed.
How Concrete and Steel are Made
Although popularized by the ease of production and use, making concrete requires an enormous amount of energy. Concrete is made by combining a sand and gravel (aggregate) mixture with water and cement to create a thick paste. The production of cement requires extreme heat, which is the main cause of high energy consumption when making concrete. Cement also accounts for 5 percent of carbon dioxide emissions globally and is considered a direct emission into the environment.
Steel, a material produced from the heating of coke, iron ore and limestone, also requires a great deal of energy. The main component, coke, is made by crushing and heating coal. The EIA reported that 3% of global coal usage can be attributed to the production of coke. Construction accounts for nearly 50 percent of steel use by volume globally, and the energy cost of producing this much steel is enormous; one tonne of steel results in roughly two tonnes of CO2 emissions on average. Both concrete and steel require a substantial amount of energy and natural resources.
Growing Reliance on Steel
The construction industry remains reliant on steel, even as demand shifts from traditional buildings to energy-intensive high rises. Steel is an ideal building material because it’s strong, relatively lightweight, corrosion resistant, recyclable at the end of its life cycle and versatile enough to be transformed into just about anything you can dream up. Steel production is expected to increase by a third between now and 2050. On a per-ton basis, steel production accounts for more than twice the greenhouse gas (GHG) emissions of concrete production.
Alternatives to Steel and Concrete
Steel and concrete are both major issues for emissions reduction under the Paris Agreement. Steel, cement and concrete account for roughly 11% of global carbon dioxide emissions at the moment, but together they could rise to up to 25% by 2050 as developing economies trend toward urbanization.
As the price of oil continues to rise, new ways are found to limit our dependence on it. So, what is an alternative to these two products? Steel and concrete can’t be replaced easily; they are low entropy materials that, as mentioned before, require a lot of energy to produce.
Concrete producers have been looking for new methods of reducing GHG emissions through new additives that would use less energy or produce fewer emissions during their manufacture. For example, researchers are evaluating wood fibers that could be used as a replacement for the cement paste. Steel has a high recyclable rate (95%), which means it can be used repeatedly for construction or other purposes.
Absolute GHG emissions from steel production are expected to go up or stay steady with increased use in cars and construction projects. Steel will continue to account for a larger share of global GHGs because there are no fully developed wholesale substitutes for steel structures at this time. It’s durability, recyclability, ease of use and low cost make it difficult to replace.
If we are locked into producing a great bit of steel for construction, energy policy makers will have to focus more on ways to reduce CO2 emissions during steelmaking instead of how to limit its use.
Steel and concrete: Since they are vital materials in shaping our urban landscape, we will continue to need them both. There are currently no comparable replacements, meaning the global decarbonization initiative may first have to target other industrial processes which are more readily modified or replaced to achieve carbon neutrality.
Andrew Schaper is a professional engineer and principal of Schaper Energy Consulting. His practice focuses on advisory in oil and gas, sustainable energy and carbon strategies.