Grace Slick sang that “We built this city on rock and roll,” but the truth is that we built this city on concrete. Concrete is one of the most widely used materials on the surface of the earth. It is also one of the major sources of greenhouse gases for our planet.
Concrete in various forms has been around for over 8,000 years, but the Romans were the first civilization who used it in construction projects similar to today. The Pantheon, built 1900 years ago in Rome, is still the largest non-reinforced concrete dome on the planet. Approximately 1,750 years after the Pantheon’s construction, the concept of reinforced concrete arose.
Reinforced concrete involves pouring the concrete around a framework of iron or steel bars. The first major piece of construction using this technology was San Francisco’s Arctic Oil Company Works warehouse, which erected in 1884.
Why use concrete
The physics that make reinforced concrete superior for construction are simple. So, pure concrete has tremendous compressive strength. A block of it supports a massive amount of weight stacked vertically on top of it. But a beam of concrete has low tensile strength. If the beam is levered out over an open space, then it can only take a limited amount of extra weight before it breaks. However, iron and steel have a very high tensile strength. The combination of concrete poured around steel produces a material with high compressive strength and high tensile strength. Hence the resulting material is strong and durable. Add on the fact that concrete can be molded into any form needed, and you have the perfect construction material.
The world relies on concrete and produces about 10 billion tons of it each year. Roads, homes, buildings, bridges, and more all contribute to the demand for concrete. So this mixture of water, cement, and rock aggregate creates the urban cityscapes of our modern world. The real character of a particular concrete mix is highly dependent on the ratio of water to cement, thus making the cement a critical component. So, where does the cement come from?
Portland cement and carbon dioxide
Water and rock aggregate common substances, so Portland cement becomes the vital produced-material in the making of concrete. The first step in the production of Portland cement involves quarrying limestone. The process then moves on to roasting the limestone, along with added clay, in a kiln and then grinding the resulting mix into a powder.
The kilns used in the process of producing Portland cement require massive amounts of energy. The limestone and clay mixture requires heating to a temperature of 1,450 degrees Celsius. Fossil fuel emissions from this “cooking” process produce about 0.75 tons of carbon dioxide (CO2) for every ton of cement. Then the second contribution of CO2 occurs when the organic components in the limestone are burned away, producing 0.5 tons of CO2 for every ton of cement. Thus, in total, every ton of Portland Cement adds 1.25 tons of CO2 into the atmosphere.
Cement production creates about eight percent of the world’s annual CO2 emissions. China accounts for over half of those cement related emissions. For perspective, the two largest emitters of total CO2 on the planet are China and the USA, with India coming in third place. But Portland cement production emits more CO2 each year than all of India.
Concrete is vital to our way of life, but it comes at a cost. Therefore we all carry a carbon footprint to sustain our urban and municipal centers. Any technologies that reduce fossil fuel usage in cement production provide a valuable contribution to reducing greenhouse gases and mitigating global warming.
ArcheanWeb:
Pavement heat in the concrete jungle (Source: ArcheanWeb) – https://archeanweb.com/2020/04/13/pavement-heat-in-the-concrete-jungle/ Also:
Sources:
Concrete: the most destructive material on Earth (
A brief history of concrete: from 10,000BC to 3D printed houses (By Nick Van Mead; The Guardian) – https://www.theguardian.com/cities/2019/feb/25/a-brief-history-of-concrete-from-10000bc-to-3d-printed-houses Also:
Concrete Facts (Source: Concrete Helper) – https://concretehelper.com/concrete-facts/ Also:
Whats the Difference Between Cement and Concrete? (Source: Concrete Contractors Association of Greater Chicago) – https://www.ccagc.org/resources/whats-the-difference-between-cement-and-concrete/ Also:
Climate change: The massive CO2 emitter you may not know about (By Lucy Rodgers; BBC news) – https://www.bbc.com/news/science-environment-46455844 Also:
Cement and CO2 Emissions (Source: Rammed Earth Consulting) –http://rammedearthconsulting.com/rammed-earth-cement-co2.htm Also:
Feature Image: Dome of Pantheon Rome (Modified) – Public Domain, https://commons.wikimedia.org/w/index.php?curid=34978