What Is Concrete and Why Are Swimming Pools Made With It?

What Is Concrete and Why Are Swimming Pools Made With It?

What Is Concrete?

from Gizmodo

Concrete is literally ubiquitous.  According to this post from Gizmodo, concrete is the most popular artificial material on Earth.  Two things that we know about concrete for certain:  Concrete will get hard and concrete will crack.  Beyond that, what is there to know?  For example, what makes concrete the ideal swimming pool structural material?  This post answers all of the possible questions about concrete, gives its origins, the chemistry behind its curing, and talks about the history and future of this versatile material.

Here is an excerpt from the post:

Geochemist Tiziana Vanorio suspects the ancient Romans first watched pozzolana hardening into cement in the seawater surrounding Campi Flegrei. They co-opted the natural process, mixing in small chunks of pumice — a porous volcanic rock that forms when superheated magma is quickly cooled. And just like that, Roman concrete was born. It became an iconic building material of the ancient world, and it’s the reason many Roman structures, including the Colosseum and the Pantheon, have survived to the present day.

After the fall of the Roman empire, the art of concrete-making was all but forgotten. It gradually returned centuries later, but didn’t become widespread again until 1824, when Joseph Aspdin developed and patented Portland cement.

The main ingredient in Aspdin’s cement? Calcium silicates, formed by heating limestone and silica-rich clays in an oven to roughly 1,100ºF. Just as Campi Flegrei had been doing for thousands of years.

Modern Varieties

Today, Portland cement is quite literally the glue that holds the world together, forming the basis of concrete, mortar, stucco and grout. The main post-Roman Empire innovation was the addition of aluminum and iron oxides, which add strength and allow the calcium silicates to form at lower temperatures.

Here’s a general recipe for Portland clinker (the dried, powdery version of cement). Proportions vary by application, depending on the desired material properties of the cement.

Cement CCN Mass %
Calcium oxide, CaO C 61–67%
Silicon dioxide, SiO2 S 19–23%
Aluminum oxide, Al2O3 A 2.5–6%
Ferric oxide, Fe2O3 F 0–6%
Sulfate S̅ 1.5–4.5%

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