Concrete Is Interesting; No Really, It Is
How often do you think about the impact of concrete on your life? You’d be a member of a large majority of the population if you said “never.” Yet, the material that is ever-present in our world and delivers enormous economic benefits also adds to global warming, contributes to flooding, clogs landfills, and releases toxic dust. It’s a challenge to make something as apparently dull as concrete interesting; so, here goes.
Concrete: A Primer
Concrete is often erroneously referred to as cement. Cement is an ingredient in concrete that is mixed with sand, gravel, and water. We don’t have cement sidewalks or highways, they are concrete sidewalks and highways.
Five thousand years ago, the Egyptians were using an early form of concrete using gypsum and lime. The Romans created a material close to modern cement to make concrete.
The Pantheon in Rome is a concrete structure that was built 19 centuries ago and was described by Michelangelo as an “angelic and not human design.”
In 1824, English bricklayer Joseph Aspdin invented Portland cement. He burned clay and limestone in his kitchen stove and crushed the result into a fine powder. It was called Portland cement because it resembled building limestone quarried in Portland, Dorset in southwest England. Highly mechanized and with many refinements this is how cement is made today.
It's Come a Long Way from Joseph Aspdin's Kitchen
From kitchen counter tops to skyscrapers, concrete is everywhere. More than seven billion cubic metres of the material is used every year; that’s enough to provide a cubic metre of concrete to every child, woman, and man on the planet.
According to the Proceedings of the National Academy of Sciences, the amount of concrete in the world, measured by tonnes of carbon, already exceeds that of all trees, bushes, and shrubs.
Concrete is virtually fireproof and can be made waterproof. It’s a bit more expensive than asphalt when used as a road surface, but it lasts longer and needs less maintenance.
“First and foremost, concrete enables prosperity. Through its affordability and availability, concrete creates the infrastructure that has allowed millions to live safe, sanitary, and prosperous lives.”
Jeremy Gregory, Executive director of the Concrete Sustainability Hub, MIT, Cambridge, Massachusetts.
Concrete poured over steel reinforcing bars gives the material greater strength and enables it to be used for large archways and domes.
We are now in a world that sounds like science fiction; in February, a 3D printed concrete pedestrian bridge was unveiled in Shanghai.
And, a group of U.S. companies has developed 3D technology to build concrete homes. Business Insider reports that “they could build a 600- to 800-square-foot home in just 24 hours for $4,000 or less.”
The benefits of using concrete seem boundless; too bad there’s a downside.
The Dark Side
The cement in concrete is toxic. This is the warning that Occupational Health and Safety requires on bags of dry premixed concrete:
“Harmful if swallowed. Causes skin irritation. Causes serious eye damage. May cause allergic skin reaction. May cause cancer. May cause respiratory irritation. Causes damage to organs through prolonged or repeated exposure. Wash hands thoroughly after handling. Do not eat, drink or smoke when using this product. Contaminated work clothing must not be allowed out of the workplace ... Wear protective gloves/protective clothing/eye protection/face protection. Use only outdoors or in a well-ventilated area. Do not breathe dust.”
According to The Guardian “concrete costs the health – and often the lives – of thousands of construction workers every year. The chief culprit is silica dust, which hangs in the air on building sites.” The fine particles cause scarring in the lungs that leads to silicosis and a lowering of life expectancy.
Silica dust has some other nasty properties that can lead to kidney disease, tuberculosis, asthma, and chronic obstructive pulmonary disorder.
Who doesn’t know someone who has had hip or knee replacement surgery? Some of that joint damage is caused by concrete.
We evolved to walk and stand on soft surfaces such as dirt, but many factory workers stand on unforgiving concrete for eight-hour shifts. Here’s The Guardian again: “Health and safety advice worldwide takes it as read that concrete floors cause ailments as diverse as varicose veins, Achilles tendinitis, and osteoarthritis.”
Concrete Doesn’t Go Away
The United Nations says that “Over the next 40 years, the world is expected to build 230 billion square metres in new construction – adding the equivalent of Paris to the planet every single week” (UN’s italics).
To make way for all that construction many existing buildings are going to be torn down. Crushing and recycling old building materials is an option, but mostly the rubble is dumped in landfills. Japan recycles 90 percent of its concrete waste, China 10 percent, and Brazil just one percent.
Separating out reinforcing bars from concrete is very difficult, not to mention teasing the aggregate away from the cement. However, it can be done cost effectively if the price of carbon is factored into using virgin materials. That only happens in a few places so most concrete debris just piles up in dumps.
The emphasis among progressive engineers and architects today is constructing buildings with the eventual demolition of them in mind.
Because so much of our built environment is made of impervious concrete, heavy rainfall that comes with tropical cyclones causes serious problems because it can’t soak into the ground. This is a significant issue in cities, as the people of Houston, Texas discovered when Hurricane Harvey hit in August 2017. Rainfall of up to 50 inches fell on the city. The hardscape, much of it concrete, meant the water simply built up and caused flood damage to thousands of homes.
If cement was a country it would be the world’s third largest emitter of carbon dioxide behind China and the United States. The business of making cement adds to the global warming problem by releasing about 2.8 billion tonnes of CO2 every year.
In Mexico, concrete has been used to combat hookworm disease. The malady affects the digestive tract and causes anemia and fatigue. It can also stunt the physical and cognitive development of children. In its larval stage it penetrates human skin through bare foot contact with contaminated soil. In 2000, Coahuila state officials ran a program to replace dirt floors in houses with concrete. The result was a dramatic 78 percent reduction in parasitic diseases such as hookworm.
- “Timeline of Concrete and Cement History.” Concrete Network.com, undated.
- “10 Surprising Facts About Concrete You Never Heard About Before.” Tiltwall.ca, undated.
- “These 3D-Printed Homes Can Be Built for Less than $4,000 in Just 24 Hours.” Aria Bendix, Business Insider, September 25, 2018.
- “Hard Living: What Does Concrete Do to our Bodies?” Peter Beech, The Guardian, February 28, 2019.
- “Global Status Report 2017.” United Nations Environment.
© 2019 Rupert Taylor