The Concrete problem

Podcasts are wonderful things.  Where else can you here an hour or people talking about concrete and the science behind it.  I was listening to an episode of Science for the People about Concrete.  I actually listened to it last week, but it had a very large impact on my thinking.  What is there to know about concrete?  Lots.

Concrete is the most common building material that Humans use. More common than brick, more common than wood.  Really.  Every sidewalk, every high rise, every sports stadium.  So much that it is the number one building material used everywhere and it is the third biggest source for Carbon Dioxide production, after power plants and transportation.  One last thing we are doing it wrong.  

The history of Concrete is at the dawn of time, the first use of Concrete was about twelve thousand years ago.  People knew that if you burned limestone in a kiln and combined it with water, the mud would heat up and turn to rock again.  People think that shamans might have used this as a show of power.  But we quickly learned that it could be used to create building materials.  It was the Romans where the use of Concrete hit its height.  Seriously, the Romans were used Concrete better than we do.  The Romans built structures with concrete that are still being used today.  They built a dome in Rome called the Pantheon that is still structurally sound.  

But we say they did not build skyscrapers.  They did not use reinforced concrete like we do.  And they didn't, that is true, but it is because they did build with reinforced concrete and they discovered that it did not last very long.  Under ideal conditions, steel reinforced concrete will last a century on average.  The Romans did not build things to last a century, they built them to last millennia.  It was recently discovered that the harbour of Caesarea in Palestine was constructed of concrete, the harbour sunk into the sea when the land subsided, but it has lasted for the better part of two millennia in the salt water.  Concrete and saltwater are considered a bad combination for building today.  

Why are we so bad at making concrete?  It is the materials we use.  We use steel as a reinforcement of the concrete.  Concrete manufacturers in the early part of the twentieth century, sold builder on e strength of their product by claiming that the concrete would seal the steel completely in the concrete and the alkaline environment of the setting concrete would prevent the steel from rusting.  Perfect.  Except that the concrete only remains alkaline for a few months and the concrete cracks.  Water enters the concrete and oxidizes the steel.  The steel expands as it rusts, creating bigger cracks, and eventually the steel breaks.  When the steel breaks the strength of the concrete is lost and the structure begins to crumble.  Additionally, construction workers leave the steel out in the elements when they are building with them, so they start to rust before they go into the structure.  The Romans made reinforced concrete, they used materials that did not rust, they were just not as strong as steel.  We could make buildings that retain their strength and will last longer, but they are a little bit more expensive, so we don't.  We use materials that will last between fifty and a hundred fifty years.  Which means that everything that we build these days will have to be torn down and rebuilt in another hundred years.  When we do that we will see that the Pantheon will still be there and working, the harbour of Caesarea beneath the waves will still be intact.  

What it would take to stop this now is a few simple pen strokes.  Simply make all reinforcement out of materials that do not rust, do not lose strength over time.  Like aluminum, stainless steel, and anything else; even plastic covered steel would be better.