Link between human body, cement a concrete one

In the corner of our garden, there is an adjacent concrete sidewalk where there is a tiny handprint. It was placed there many years ago when one of our grandsons was newly born. He was born the same year we moved into our home and poured the sidewalk. It is a nice memento. The only other time I messed up fresh concrete was when I was about 8 years old, and that time I was in big trouble.

But back to my grandkid’s handprint. As I recall, we were sitting around after dinner with our son and his wife and new baby. Someone asked when the new concrete would be dry. Of course, I had to explain to them that concrete doesn’t dry out. Quite the opposite, it sets. There is a lot of water in concrete; it’s just locked up in the microstructure of the cement. That’s one of the reasons concrete is waterproof. There’s no room to take up water because of the water already inside.

Oh, and by the way, there is a difference between concrete and cement. Cement is the stuff that locks up the water, and concrete is cement with added rocks, iron, or other bulky material to increase volume and strength. It turns out that cement binds with many solid materials quite well. A French gardener was the first to discover he could place metal rings in cement pots to strengthen them. But that’s another story. I guess the amazing thing is that he didn’t have an NSF grant to fund his work.

To make cement you mix large amounts of calcium carbonate and silicon with lesser, but precise amounts, of aluminum and iron in water. The chemicals must all be ground and heated into a very fine powder. When water is added, the powder sucks it up in surprising amounts and turns it into a wobbly, semisolid gel. Toothpaste is another kind of gel, but you wouldn’t want to confuse the uses of the two.

Gels have an internal structure that gives them form and doesn’t allow the water to slosh about. In cement, this internal structure is created from calcium silicate crystals that grow when the two compounds, calcium carbonate and silicon, are dissolved in water. As these crystals form over time, they trap the water into their bonds and internal structure. Eventually, the crystals fuse together changing the material from a gel to a solid mass, locking the water inside.

My wife was so enthralled by my explanation of why concrete doesn’t “dry” that she immediately wanted to put her new grandson’s hand into the fresh concrete to preserve the memory of my explanation. Interestingly, the child was less enthralled and howled like a banshee when we stuck his hand in the stuff. I suppose today what we did would be considered some kind of child abuse.

Anyway, the point of all this is that it just recently dawned on me that all the ingredients used to make cement are found in the human body. Calcium carbonate is found in bones and the blood stream. Silicon is important in forming cross linkages in bones and in fingernails. Iron is an essential component of blood and aluminum is even found in trace amounts throughout the body. Then, of course, we are mostly water! 

The only thing missing is the ability to heat the human body to about 1450 degrees Celsius. Admittedly this is about 900 degrees hotter than your oven at its best. Still, what if we found an enzyme that would allow the reaction to occur at a lower temperature? Such an enzyme would become invaluable to industry, but it could also explain how people sometimes become more rigid and set in their ways over time. Not me, of course. Just other people.

While this is just theory at this time, it would probably be prudent to avoid overheating in these dog days of summer.   

Gary McCallister, .(JavaScript must be enabled to view this email address), is a professor emeritus of biological sciences at Colorado Mesa University.


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