Thread by @EdConwaySky

What’s the most underrated material in the modern world?
How about CONCRETE?
Often dismissed as boring, ugly & inert.
Concrete is actually surprising, dynamic & incredibly complex.
With that in mind here are a few reasons why we need to start talking about concrete 🪨
🧵

First off, we use a lot of it. A hell of a lot of it.
Every minute of every day, construction firms around the world pour out the equivalent of more than 200,000 bathtubs of concrete.
Every minute.
Every year we pour enough concrete to cover the entire landmass of England.

The vast majority of concrete these days is being poured in China, to build bridges, skyscrapers, high speed rail etc.
Indeed China produced more cement in the past three years alone (2018-2020) than the US did in EVERY year since the first Portland cement plant opened in 1865.

Or another way of looking at it. Here is the total amount of cement produced in the US over the past decade vs the amount of cement produced in China in the same period. You get the idea.

At this stage you're prob wondering about why I'm saying both "cement" and "concrete". Actually they’re slightly different things. Cement is the magic ingredient inside concrete. Concrete is basically sand plus gravel plus cement. Add water and you get an extraordinary reaction.

Calling it extraordinary isn't overdoing it. The cement reacts with the water to create a kind of gel which quickly and then slowly begins to cure into stone. Look under a microscope and you see lots of tiny stony tendrils forming which bond to each other and the sand/stone.

Scientists still don't 100% understand what's going on inside cement when it's setting. In chemistry labs this remains hotly-debated territory. Also intriguingly, it keeps on curing long after it's apparently set. The Hoover dam is still curing nearly a century after being built!

But the upshot of the chemical reaction is to create a kind of stone you can pour into a mould. Hard these days to imagine how revolutionary this was back in the 19th century when the main alternative was bricks/masonry which was v labour intensive and considerably less strong.

Concrete is very, very strong, especially when you combine it with steel reinforcement bars (rebar) which also give it tensile strength (so you can build bridges with it). The 20th and 21st century world is literally built on concrete, mostly reinforced concrete.

Now, we are not the first civilisation to be v reliant on concrete. The Romans had their own form of concrete & there's evidence our ancestors used a form of cement as long as 10k yrs ago. The Colosseum is partly built out of concrete, behind the brickwork and in the foundations.

That brings us to the most amazing building in Rome: the Pantheon. An enormous, pristine, beautiful and quite delicate-looking dome, all built out of concrete TWO THOUSAND YEARS AGO. It's still the world's biggest unreinforced concrete dome even today.

But while modern concrete is stronger than Roman it tends to last less long. This is usually down to corrosion of the steel bars inside. A big problem these days esp in highway maintenance. Many bridges get this problem. Eg lots of these (not Hammersmith) thetimes.co.uk/article/half-o…

Anyway, after the fall of the Roman Empire, the recipe for concrete was forgotten. Only in the 15th century, when an old manuscript by Vitruvius resurfaced with hints about the recipe, was interest in this building craft re-ignited. It sparked a race to "re-invent" concrete anew.

When historians write abt the enlightenment, industrial revolution etc, they often talk about steel and science and electricity and so on. They tend to overlook concrete & cement. But in the 18th and 19th century many of the world's greatest minds were focused on this challenge.

There were countless contenders making artificial stone but the eventual winner of this race was someone called Joseph Aspdin, who patented Portland cement in 1824 (the "Portland" bit was essentially a branding exercise, since Portland stone from Dorset was v fashionable).

No-one is quite sure, by the way, whether Aspdin came up with the recipe himself or nicked it from someone else. If you're interested in this topic and, well, concrete more generally, Concrete Planet by Robert Courland is well worth a read amazon.co.uk/Concrete-Plane…

Anyway, Portland cement wasn't quite the same as the Roman variety, whose secret ingredient was a kind of volcanic ash called Pozzolana. In most ways it's actually stronger. Tho in terms of water resistance we are still learning much from the Roman variety eurekalert.org/news-releases/…

To simplify enormously, Portland cement is a powder formed when you roast limestone/chalk with clay, sand and, occasionally, other additives such as iron oxide. You end up with black, unpromising-looking nodules, which are called clinker. Crush them and you have a basic cement.

This all happens in a kiln. Back in the day these were "bottle kilns": like those old pottery kilns you see in Stoke-on-Trent and elsewhere. But these days they are rotary kilns, vast, hot, titled tubular ovens through which the ingredients tumble as the chemical reaction occurs.

I went to the cement plant in Rugby the other day. It was unexpectedly thrilling. The kiln is the enormous tube here (not the tall tower where the chimney is, which is kind of pre-heating the ingredients).

The kiln here is the biggest in the UK. This plant is actually the oldest still operating in the UK - possibly the world. This plant was making cement for the Victorian industrial revolution. Cement during WWI and WWII. Cement today for HS2 and more.

The kiln has to keep turning, 24hrs a day, partly because of all the demand for cement (LOTS post Covid) but more importantly because if it stopped the heat inside would melt the tube and it would sag & fail. This would be v bad, the plant manager said, with some understatement

Cement plants don't get much attention. Manufacturing stories fixate on car plants/steelworks but cement is a crucial part of the economy, because of how many sectors it underpins (construction, property, transport). & unlike most sectors we're nearly self-sufficient in cement.

But there's growing focus on kilns these days, because cement happens to be one of the trickiest obstacles in getting carbon emissions down to net zero by 2050. Cement is responsible for roughly 7% of global emissions. More than aviation & deforestation combined. It's a BIG deal.

Actually that 7% comprises two parts: the chemical reaction as calcium carbonate (chalk/limestone) is heated and the carbon bonds with oxygen, creating calcium oxide (quicklime, key component of cement) & co2. Then the emissions from the kiln's heat source, traditionally coal.

Its relatively straightforward to remove coal from the equation. The Rugby plant (run by Cemex these days) uses Climafuel - essentially processed waste - to heat its kilns. Here's the big hangar where they store it. The grabber picks up the fuel and sends it to the heating tower.

This plant - and the UK cement industry - is FAR greener these days. In this country cement CO2 emissions are down 53% since 1990 - partly by reducing energy emissions, partly by adding things to the final mix. But the CO2 from that chemical reaction is a far tougher nut to crack

You can't achieve the chemical reaction in the kiln w/o carbon emissions. So for the cement industry the only foreseeable way to get to zero emissions is via carbon capture & storage. And CCS is v expensive and while the tech works in theory we've yet to see it applied at scale.

Raising another q: can we make cement without emitting co2? Yes and no. One alternative is alkali-activated cements where you add an alkali solution to blast furnace slag or coal fly or waste incinerator ash or metakaolin. You get a really strong cement w/o direct co2 emissions.

Few weeks ago @BrantWalkley and his team at @sheffielduni mixed us up some samples. On the left is traditional Portland cement. Middle is alkali-activated, reducing emissions by c.80%. On the right is one that is zero carbon!*

* Whether it's really zero carbon depends on how you do the accounting. Because it was made with blast furnace slag, some carbon WAS produced by the steel mill from which it came, if not in the cement reaction. Account for this carbon and it's not zero emissions

This alkali-activated cement is also more resilient to rebar corrosion. Why? It has a higher pH than traditional Portland cement, which helps protect steel from rust. These alkali activated cement blocks have been sprayed with a solution which goes pink when there's a high pH.

Remaining question: how well these cements stand up to real world use/abuse over decades. We have 200yrs of Portland cement but much less with these ones. Tho there are one or two structures around world made with alkali-activated cement, esp, surprisingly, in the ex-Soviet Union

Faced with shortages of Portland cement in the Soviet era, some chemists/builders experimented with these unconventional cements. Here's an apartment in Mariupol, Ukraine. Tho few of its residents realise, this building is a site of deep interest to scientists these days.

There's also a jetty at Skinninggrove in N Yorks built with cement made w/ blast furnace slag, long before Soviet efforts. Only prob? It got renovated recently & I think (tho yet to be confirmed) the renovation used Portland cement, not the unique mix with which it was first made

But while these kinds of cements are much greener the problem is they're quite hard to scale up. And the defining feature of concrete is scale (back to those first few tweets). And ease of use. One of the most amazing things about concrete is that pretty much anyone can make it.

If we're going to continue relying on cement (hard to imagine 21st century civilisation without it) and hit net zero we need some BIG technological leaps - soon. Lots of 💰 going into batteries/hydrogen/solar etc. But this issue, unsexy as it might be, is also v v important.

If you're still, god forbid, interested in cement and concrete after all that, here's a short @SkyNews film I made with @maddylratcliffe about it

A few more cutting-edge concrete links.
Concretene (concrete + graphene). Stronger & greener than Portland cement: nationwideengineering.co.uk/concretene/
Hemp concrete. Potentially carbon negative! sciencedirect.com/science/articl…
Glass fibre-reinforced concrete (corrosion proof)
cemex.co.uk/fibre-concrete…

The challenge with all these ideas is not merely whether they work, or indeed whether they can theoretically be scaled up, but also persuading the construction trade to take a leap and adopt them. Which, it turns out, is v hard indeed (h/t @adepledge): constructionphysics.substack.com/p/why-its-hard…