Sunday, June 23, 2024

Calgary pipe - the legacy of 70's concrete

 I lived through a lot of this, and I looked it up as an engineer doing tunnels and such.  The same issue that hit Calgary, has been hitting northern bridges.  I have a feeling they will have to replace the whole water main, and that this repair will only last a few months before another section goes.

In the 60's we built with a lot of concrete and little steel.  You still see a few of those bridges on the 401.  Then in the 70's there was a huge push for more modern concrete.  It was a great time for the civil engineering labs in the universities.  In the lab, they found they could get away with more pre-stressed steel, and less concrete.

Unfortunately, they were wrong.  Less concrete meant 'less cover' on the steel.  With the road salt on the bridges, the concrete let the salt attack the steel.  Then the rust expanded and cracked the concrete more.  The northern US had bridge collapses, and Canadians decided to replace all those bridges.

We now use steel that is coated with epoxy.  Very careful installation to make sure all the chips are fixed.  This steel, embedded in concrete, can last a very long time.

70's concrete was also horrible in earthquakes because the joints had the strength, but not the stiffness.  They tend to pancake.

All those 70's concrete pipes will now have to be replaced.  I hope they are all only in Alberta...

No comments: