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Don't paddle away in a hurry. I know what you are going to say: "Concrete? Isn't that just cement and water? Is this considered high technology?"

Yes, it's filthy and dusty, and even its name has a cheap feel (Concrete, the etymology of which even means "to harden" is so perfunctory).

But you may not be aware of a terrifying statistic: Concrete is the most consumed substance by humans on this planet, after water.

If all the concrete used by all mankind in a year were piled into a wall, it would circle the earth along the equator. The houses we live in, the bridges we walk on, and the tunnels we drill are all essentially made of this "liquid stone". We think we live in the information age, but in fact if you peel back the earth's crust and take a look, we are still living in the Stone Age, but this time the stones are made by ourselves. **

But what I want to talk about today is not how great it is, but how "holey" it is.

This thing hides a "ticking time bomb" of modern architecture.


1. The “black technology” of the Romans and our “short-lived ghosts”

Have you ever traveled to Europe? If you've been to the Pantheon in Rome, you'll have seen that huge concrete dome.

It stood there for nearly 2,000 years. Wind, rain, earthquakes and wars have kept it motionless, with very few cracks.

Look at our current building again.
The design life of general commercial housing is 50 to 70 years. Many viaducts and dams have been repaired and repaired after being used for 30 or 40 years. The concrete has peeled off and the steel bars have corroded.

Have we regressed? We have purer cement, more sophisticated mixers, and more powerful chemical additives, but the things we create are not as strong as those made by a group of ancient Romans wearing straw sandals?

This matter has puzzled scientists for hundreds of years, and it was only recently that the case was solved.

The Romans' concrete formula included a "wild" raw material: volcanic ash, and seawater was used for mixing.

Modern engineers would go crazy if they saw this recipe: the salt in seawater is the natural enemy of concrete! But the Romans were so fierce. When seawater, volcanic ash and lime mix, an extremely slow chemical reaction is triggered, producing a rare mineral called tobermulite.

This mineral acts like glue, growing over hundreds of years to seal the cracks back to themselves.

In other words, Roman concrete is "living". The older it gets, the harder it gets, and the more it is soaked in sea water, the stronger it becomes.

Our modern concrete pursues fast. Quick drying, early strength, high grade. We sacrificed "longevity" in exchange for "speed." This is why urban construction seems to be speeding up now, but maintenance costs are like a bottomless pit.

2. Steel + concrete = a marriage doomed to divorce

The most deadly invention of modern architecture is called "reinforced concrete".

This sounds like a perfect couple:
Concrete is like stone, not afraid of pressure, but breaks when pulled (extremely low tensile strength);
Steel bars are like muscles, they are not afraid of being pulled, but they bend when pressed.
Put the two together like "muscles and bones", which can resist both compression and tension. They are simply invincible. Skyscrapers can only stand upright thanks to this method.

But there is a huge Bug here.

While their coefficients of thermal expansion are miraculously aligned (a complete coincidence, otherwise these two wouldn't be together), their lives are completely out of sync.

Concrete itself is porous, it acts like a hard sponge. Carbon dioxide and water vapor in the air will slowly penetrate.
Originally, concrete is highly alkaline and can protect the steel bars inside from rusting. But over time, carbon dioxide will "carbonate" the concrete and make it less alkaline.

Once the protective layer fails, the steel bars inside will begin to rust.

Do you know how many times the volume of iron will expand after it rusts? 4 to 6 times.

Imagine that the blood vessels in your bones suddenly expanded six times. What would happen to your flesh?
burst.

This is "concrete cancer." Rusted steel bars will burst the concrete from the inside, and large chunks of cement will peel off, exposing the rusty skeleton inside.

This is the fate of modern architecture. From the moment of pouring, the countdown begins. The skyscrapers we are proud of will become dangerous buildings in less than 100 years without expensive maintenance.

3. We are almost out of sand (don’t laugh, I’m serious)

This sounds like a joke: There are so many deserts on the earth, you tell me there is a lack of sand?

This is another counter-intuitive knowledge point in materials science: Although there is a lot of sand in the desert, it is all useless wood.

Due to wind and sun, the desert sand particles are worn too round and smooth. If you mix them into cement, it's like building a wall with a bunch of glass balls. They won't stick together at all and will fall over as soon as you push them.

The sand that can be used for construction must be river sand. After being washed by running water, the edges and corners are retained and the friction is high, so that the cement can be locked.

So, a ridiculous scene happened:
Across this planet, humans are frantically hollowing out river bottoms. Even some countries (such as the United Arab Emirates) spend a lot of money to import sand from Australia to build the tallest building in the world, although the entire country is built on sand.

In order to grab sand, a "sand mafia" has even emerged around the world. The illegal mining of river sand has led to the collapse of bridges and ecological destruction.

You see, what seems to be the cheapest material is actually a bloody resource war behind it.

4. Can the future “heal itself”?

If the Romans could do it, can we replicate it?

Material scientists are now working on a very disgusting black technology: bacterial concrete.

When they mix the concrete, they add some special Bacillus bacteria and calcium lactate into it. These bacteria are usually dormant, as if dead.
Once concrete cracks, rainwater seeps in, awakening bacteria. After these guys had eaten and drank enough, they started to "poop".

What they excrete is calcium carbonate (that is, limestone).

These bacteria will multiply and excrete wildly in the cracks, filling the cracks with their own metabolites. This is just like if you break a bone, your body will automatically grow a callus.

Currently, this technology is still in the laboratory stage and the cost is prohibitively high. But if it is mass-produced one day, maybe our houses can really have the vitality of self-healing like living things.


Conclusion

The next time you walk by those dusty viaduct piers or touch the cold walls of your home, stop thinking of them as dead objects.

They are actually a grand chemical experiment, a love-hate entanglement between steel bars and cement, and human ambition to use flowing stones to fight against time.

Although they are destined to weather, crack, and crumble, until then, they do support the weight of our entire civilization.

This is the roughest and most romantic side of materials science.