Image Source: Pixabay

We could take millions of steps on something during our lifetime and not know even what it is.

It wasn't until earlier this year that I found out what concrete is and why it doesn't reabsorb water after it's dry. Think about it, many things that have dried out reabsorb water like pasta, sponges and wood. Why then does concrete not become soggy when it rains? The answer lies below in this photograph of concrete which shows chemical reactions with water:

Image Source: Maria Amenta Wikimedia

Concrete is made by combining cement, water, and aggregates such as sand and/or gravel.

When mixed together, this makes a slurry which has the consistency of thick cake batter. The most common type of concrete is made from Portland cement which was developed from natural cements made in Britain beginning in the middle of the 18th century. By burning limestone and clay together at very high temperatures, you get Portland cement. But what specific compounds are contained in Portland cement? Tricalcium silicate, dicalcium silicate, tricalcium aluminate, tetracalcium aluminoferrite and gypsum are in it.

When you add water to the cement and aggregates, various chemical reactions occur which create a hard matrix that binds all the materials together. When these chemical reactions are happening, it’s better to think of the concrete as curing instead of drying out. So the term drying out doesn't exactly apply to concrete. But what exactly is going on in the concrete?

When water is added, each of the compounds undergoes hydration and contributes to the final form. Only the calcium silicates contribute to strength. Tricalcium silicate is responsible for most of the early strength, in the first seven days. Dicalcium silicate, which reacts more slowly, contributes to the strength at later times.

These chemical reactions form calcium silicate hydrate which then grow into crystalline fibers which bind to each other and quite literally, cement the entire mixture together.

Image Source: Wikimedia, Betonchik

The reason that concrete doesn’t dry out and then reabsorb water later is because water isn’t leaving the concrete at all.

It’s reacting with it and becoming part of the concrete form. Concrete continues to set and cure for months and years, increasing its strength over time. It’s a long-lived giant chemical reaction that continues on long after it has set. And our world would be very different without it. Imagine for a second: no concrete.

This video explains this process quite well:

It’s a good thing concrete doesn’t reabsorb water after it has cured. Can you imagine what a soggy bridge would be like to drive on?

If you want to learn more technical details about concrete, go here.

My article first appeared in Interesting Engineering. It has been modified, added to and rewritten.

In the next THAT'S FU#%ING SMART post, we'll discuss how wi-fi works.

ps- I'm currently experiencing digital hangovers in the form of debilitating migraines and therefore, I've placed myself on an information diet. I'm not on Steemit Chat, so if you want to reach me, the best way is through Twitter or here. My handle on Twitter is @stellabelle. I apologize to anyone who has tried to contact me via chat. I've also stopped using chat because I felt I wasn't terribly productive. I'm in a low productivity cycle, so every ounce of my energy has to be utilized efficiently.