The constructed city as we know it all started with a flower pot in a French garden.
It was in 1846 that Joseph Monier, the sixth child of a poor family of horticulturalists from a small French village, began working in the Tuileries gardens in Paris, near the Louvre. He had never been to school – didn’t need to, his mother said; he was smart enough.
Monier spent a lot of time repotting plants. Most of the pots in the royal gardens were made of wood, which weathered badly and rotted quickly. He began to wonder whether there wasn’t a better material, something that would last longer.
Then he began experimenting. Clay didn’t work much better; it broke easily and would crack when temperatures changed rapidly. Concrete looked like a good option, but containers that were strong enough had to be so thick that they became practically immovable. The problem occupied him for years.
Without understanding the science behind it, Monier had discovered that concrete and iron are a match made in heaven
Until he hit on an idea, that is. What if he embedded an iron mesh in the concrete? It made the pots a good bit lighter and also kept them from cracking in the event of a sudden spring frost. Without understanding the science behind it, Monier had discovered that concrete and iron are a match made in heaven. The two materials expand at the same rate, and the combination is fantastically strong but still relatively light.
In 1867, this French gardener patented his idea and forever changed the way we build cities. What started with Monier’s flower pots near the Louvre is today the secret to all our skyscrapers, viaducts and tunnels – essentially all of modern architecture.
Monier had invented reinforced concrete, the material that has shaped the modern age – literally.
Reinforced concrete has enabled us to build great things, but this building material is also extremely problematic. Producing it generates far more CO2 than even the air travel industry could hold a candle to. But could we ever do without it?
Concrete to the sky
Long before Monier began experimenting with his plant containers, concrete was already known to be a useful material. The Romans built an empire with it. Opus Caementicium went into aqueducts, the Colosseum, a European network of roads spanning some 85,000 kilometres and, of course, the Pantheon in Rome, which is still the world’s largest dome made of non-reinforced concrete at 43 metres across.
Concrete is a composite material made of 60-75% sand and gravel, 15-20% water and 10-15% binding agent – the crucial ingredient holding it all together. The Romans used a volcanic ash known as pozzolana. In modern concrete, that binding agent is called “Portland cement”.
Concrete has tremendous compressive strength but very low tensile strength. This makes it great for building the support pillars of a bridge, for example, but not the connecting elements between the pillars. Gravity would stress the spans to the breaking point, causing the concrete to crack. That’s why a Roman aqueduct has so many arches: they transfer the tensile forces on the span, transforming them into a compressive force on the pillars. In a modern bridge, this is unnecessary; with the addition of metal reinforcing elements (now made primarily of steel instead of iron), concrete can handle both compressive force and tensile force.
This combination of qualities is what makes reinforced concrete an ideal building material.
Still, there was a healthy degree of scepticism in 1903 when the first “skyscraper” constructed from reinforced concrete – the 16-storey Ingalls Building in Cincinnati, Ohio – went up. One year earlier, the building permit application for the Ingalls had been rejected; the building inspector found the design too experimental and had concerns about the building’s safety. Many were convinced that the building wouldn’t last a day after the construction supports were removed. The story goes that one reporter even camped out during construction, watching the building the whole night through, hoping to document the moment of collapse. But it didn’t collapse. When the building was topped out and the flag ceremoniously raised on it, The Cincinnati Enquirer wrote: “It is now assured that the building is a success.”
It’s still standing to this day.
Edison’s dream: concrete houses
One of the first to fully embrace reinforced concrete was American inventor Thomas Edison. “Concrete houses are the future,” he argued as early as 1906. “Concrete is resistant to fire, termites, mildew, rot, and natural disasters.”
Yes, that Thomas Edison – the same Edison as the electric light bulb – who also happened to be the director of the Edison Portland Cement Company.
Today, no material has given more people a roof over their heads than concrete
Edison had big plans for concrete, and one of them was mass production of houses. He had a vision, and that vision was producing a two-story house from a single mould and a single casting – including furniture, which would also be cast in concrete.
But large-scale production of Edison’s design never got off the ground; it was simply too complex. The inventor’s dream was that his houses would be the “salvation of the slum-dweller”, but in the end, that proved to be exactly the reason that few people wanted to live in them: nothing embodied the working class quite so much as a concrete house.
Though his houses never overcame their image problem, Edison was right about the concrete. Today, no material has given more people a roof over their heads.
The list of its advantages is long. In a home, concrete keeps things cool under the summer sun and holds the heat in during a cold winter. It’s also a simple material – so simple that, with a single concrete mixer and a little help, anyone can put up a concrete house. Sand and gravel are still cheap and plentiful, and cement is priced at around 10 cents a kilo, making it affordable for almost everyone. And it lasts a long time – really long, as the early proponents of concrete proclaimed, pointing to the still-standing construction works of the Roman Empire.
The most popular construction material in the world
Future archaeologists will use concrete as a geological boundary for the start of the modern age, because right now, in the early 21st century, reinforced concrete is by far the most widely used construction material in the world. Half of all buildings on Earth are made from it, and more than 70% of the world’s population lives in a building containing reinforced concrete. Humankind has paved the landscape with it and covered whole mountains with the stuff. The largest chunk of it in the world today, the Three Gorges Dam – a 27 million m3 block of concrete reinforced with 500,000 tonnes of steel – holds back the Yangtze River in China.
In the USA alone, concrete is a $37 billion industry that employs over 2 million people. The value of the worldwide cement and concrete market was estimated at $439 billion in 2018 and is expected to grow to $652 billion in 2022.
Economies of developing countries can be measured in tonnes of poured concrete. Between 2008 and 2010, China alone poured more concrete than the whole United States did in the entire 20th century – and there’s no end in sight. The amount that China adds every year would be enough to cover a small country (like the Netherlands) completely in a sheet of concrete 15 cm thick.
For architects, concrete means freedom
Reinforced concrete is good for more than just mass production; it opens up whole new worlds of possibilities for the architect. While the finished product generates associations of the monolithic and monumental – the proverbial “concrete block” – its most interesting quality for the architect is its starting state: fluid. This critical quality means that whatever you can imagine, and whatever you can make a mould for, you can build out of concrete. Building an extravagant new concept or a reproduction of the Parthenon? With concrete, it’s no problem – and available for a fraction of what it would cost in any other material. For architects, concrete means freedom.
Concrete is modernism and modernism is concrete. The Sydney Opera House, Frank Lloyd Wright’s Guggenheim in New York and virtually any iconic building of the modern world all owe their existence to reinforced concrete. The celebration of the material reached its architectural high point in the mid-20th century with the work of Le Corbusier, Béton brut and New Brutalism.
And then the problems started.
You get what you pay for
The concrete buildings of the 20th century are gradually starting to crumble away. Alas, it seems the initial promise of eternal stability that had kept Roman construction works standing after 2000 years does not hold up for modern reinforced concrete.
It turns out that reinforcing concrete with steel makes it strong in the short term but susceptible to concrete rot as time goes on because iron or steel reinforcement rusts, even if it’s inside the concrete. There the corrosion grows and gradually breaks the concrete apart from within. So, unlike concrete without reinforcement, reinforced concrete needs continual maintenance. And that maintenance will exceed the cost of the building itself many times over. Do nothing, and you can expect your reinforced concrete to last 30, 40, maybe 50 years.
In the United States, virtually every piece of infrastructure containing reinforced concrete was given poor to failing marks for their current state of maintenance. Bridges came out best, scraping by with a score of 60%, while dams, irrigation works, schools, airports and wastewater facilities all failed miserably at 40% – and that’s with maintenance costs already in the billions of dollars. Expect China to start suffering from the same problems, only much worse, after 2030.
Europe, too, got a wake-up call in 2018. In 1967, the Morandi Bridge in Italy, near Genoa, was one of the longest reinforced concrete bridges in the world. 51 years later, on 14 August 2018, that bridge suddenly collapsed. The cause: poor maintenance.
You get what you pay for.
Cement is the biggest polluter
Eventually, the bill comes due, and it doesn’t just hit us in our wallets. The real damage is being done to the climate.
Because of the vast scale of our use, we’re now running into problems with virtually every ingredient that goes into reinforced concrete. As quality sand begins to be in short supply, “sand mafias” are springing up, plundering whole beaches for the resource. Meanwhile, the steel industry that concrete relies on for its rebar is also one of the most polluting industries in the world. But the most problematic and polluting element of concrete is the cement.
The cement industry is a wholesale consumer of water. It accounts for no less than 9% of worldwide industrial water consumption (1.7% of mankind’s total water use). That much water consumption is a threat to the water supply in many countries.
And last but not least, part of making cement involves heating limestone to a temperature of 1500°C for an extended period of time. That produces huge amounts of CO2. Cement accounts for about 80% of the CO2 generated in the production of concrete. A lot of that is the fossil fuels burned to reach that temperature ( 2 to 3% of total annual energy consumption goes into cement production), but even more of it comes from the process itself.
All in all, every tonne of cement means 822 kg of CO2 going straight into the atmosphere. The total emissions from the production of cement over 90 years (1928 to 2018) are estimated at over 38 billion tonnes, 71% of which was generated after 1990. In 2019, the world produced 4.1 billion tonnes of cement. China accounted for 2.2 billion. According to the most recent article in Earth System Science Data, the cement industry is responsible for no less than 8% of global CO2 emissions.
If we intend to systematically reduce our CO2 emissions and avoid spending unsustainable amounts of money on concrete maintenance, we cannot go on producing anything like these quantities of concrete. That’s one reason why architects are increasingly looking to alternatives like wood. The problem is, none of these alternatives have the same combination of qualities: cheap, strong, safe, fire-resistant, disaster-resistant (if properly maintained) and, above all, fluid – and therefore mouldable.
“Concrete shaming” is a term recently introduced from an unexpected corner: Dorien Staal, who chairs the Dutch Concrete Association.
However, in an interview, she made it crystal-clear that she herself is not ashamed of concrete. “Of course not,” she says. “It was meant as a wake-up call for the sector.” Even though there is a Dutch “Concrete Accord” from 2018, in which the Dutch government made commitments on increasing sustainability in the concrete industry, Staal still feels that too little concerted action is being taken, despite the knowledge available in the sector.
Elsewhere in the world, we see that there are other initiatives to make concrete more sustainable. In one promising development, replacing steel reinforcement with carbon fibre seems to make the material truly low maintenance. In another, using very high-strength concrete has been shown to require far less material; this was done in the construction of the new One World Trade Center in New York City, which also incorporated a significant quantity of recycled material. But knowledge-sharing about sustainability improvements in the concrete world is piecemeal at best. With her own company, Staal is trying to set an example of how things can be different. Working closely with leading engineers (ABT) and knowledge institutions (TU Eindhoven), they are testing new, more sustainable recipes for concrete and sharing all knowledge gained with the entire sector.
That’s critical when it comes to the cement in particular, Staal says, because “The Holy Grail is a sustainable glue between the grains”.
Sustainability initiatives in the cement industry
Since 1990, the biggest cement companies in the world have succeeded in reducing their emissions by some 20-25%. Those gains have primarily come from more efficiency in fuel use, as well as replacing some Portland cement with fly ash and blast furnace slag. Fly ash is the residue from the combustion of coal. Blast furnace slag is a by-product of producing iron. This is a win-win situation, because the waste products from one industry are being used as the raw material for another.
Meanwhile, the EU is investing in projects to increase the sustainability of the cement industry further, like an emerging technology for the capture and underground storage of up to 95% of CO2 emissions from cement factories. This would put 99% of the CO2 emissions underground for the next 1,000 years.
But are we really being honest with ourselves about these solutions? Fly ash and slag are both by-products of other polluting industries that we should really be trying to eliminate. And doesn’t underground storage of CO2 essentially amount to sweeping the problem under the rug?
Wouldn’t we be better off facing up to the fact that the only real solution is finding a genuine alternative to Portland cement?
The craftsmanship of the ancients
That brings us back to the Romans. I already said that they used a particular volcanic ash in their cement, but they also used a lot less lime. Pliny the Elder wrote that the concrete they made with these ingredients became “stronger by the day”. It turns out, he was right. Look at all the Roman buildings that are still standing today, 2,000 years later. Now, that’s craftsmanship, wouldn’t you say? Or might there be something more at work here?
In recent years, there has been a lot of research into the various types of Roman “cement”, particularly the one they used to build their seaports – the foundations of which have survived, even submerged as they have been in salty seawater all this time.
It’s a complex story. The volcanic ash that the Romans mixed into their concrete turns out to contain a mineral called phillipsite. In contact with seawater, a chemical reaction occurs that forms a different, rare mineral: tobermorite. Over time, elongated flat crystals form that hold the concrete together and, at the same time, give it flexibility. So indeed, as Pliny the Elder wrote, their concrete really did get stronger over time. And not only that, but the Romans seem to have stumbled on something that looks suspiciously like a natural form of rebar that grows itself.
How could they have known this? Well, they almost certainly didn’t, but craftsmanship doesn’t mean you have to know why a material has certain qualities – think back to Monier, who solved his flowerpot problem without any formal education at all. What matters is that you are able to recognise these qualities and use them.
Now that we’ve unravelled the details of the Roman concrete recipe (and that’s something that only happened step by step over the past 10 years), it would be a whole lot easier to invent a modern, sustainable version. And there are people working on exactly that right now. There are currently tests going on with ashes of various kinds – not only volcanic, but more unconventional choices as well, like the ashes of hazelnut shells.
These are the kinds of alternatives we need – desperately. Without a sustainable solution, the day might come in the foreseeable future when we have to say goodbye to concrete for good – something our society can’t afford to do anytime soon.
Concrete is the mentality of our modern age in material form: fluid, cheap, abundant, monumental, grandiose but also brittle.
It suits us – all too well.
Translated from the Dutch by Kyle Wohlmut.