Concrete at Carcassonne

I have a friend who drives a BMW.   He tells me that the navigation system it comes with is crap, and he always uses his Tom-Tom instead.  By contrast, I have always found the satnav on my Peugeot to be reliable and easy to use.  I have discovered two minor faults.  The first is that when directing you along switchback mountainside roads, it tends to underestimate the journey time quite severely, and secondly, if you choose the 'short route' option instead of 'fast route', it gives its sense of humour free rein, sometimes sending you down donkey cart tracks in order to test your courage, resolve, suspension and 4-wheel-drive.  The Peugeot doesn't have 4WD.

We chose the 'short route' option when travelling from Carcassonne to the suspension bridge at Millau.  It had calculated 2 hours for the fast route, and 2 1/2 for the short route, so we figured we might as well take the slow road and see some scenery.   It sent us down some very pretty switchback roads on the Black Mountain that is the source of the water for the Canal du Midi and we got to see some very fine scenery.  But, despite my best efforts through the hairpins, the calculated arrival time moved steadily later and later, and, what with a stop for coffee, and to take some scenic photos, and then a slow lunch, we took from 9:30 to 2:30 to get there.

But the bridge is worth seeing.  There is a useful information centre you can visit, and several viewpoints where you can take photos.

One thing that I didn't know was that the original patent for pre-stressed reinforced concrete was filed by a French guy.  Although I know that reinforced concrete is made by pouring it over iron reinforcing rods (I have made some myself), I didn't know what the pre-stressed part of it implies, so I asked my Dutch pal Leo who is a concrete expert:

Concrete, like rock, is very good at supporting compressive loads, but is weak under tension.  Pre-stressing the concrete is done by first stretching the iron reinforcing rods, pouring the concrete over them, and when it has set hard, releasing the tension in the rods.  This gives the concrete greater strength under tension.   There's quite a lot of it used in the bridge.   OK, so it's not at Carcassonne.  But it's not that far away.

We came back the fast route.