I have just replaced some TV coax which ran behind a U shaped plastic channel from my ground floor to my attic (2 storey house)
The downstairs wall is built using white bricks. The upstairs wall is built using a grey/blue block which has a finer texture and lighter colour than normal breeze block.
It would appear that the side (if you can have that for a round object) of the cable which touched the blocks has turned black, and the plastic sheathing is much more brittle than the cable which touched the bricks, some of which is like new.
This in itself has not been a problem and the cable worked fine, for the 25 years (or so) that it has been in place. It would appear to have a central copper conductor, but the outer braiding looks as if it could be aluminium. There was also a foil. The main reason for replacing the cable was that I wanted to run a CAT 5 cable next to it, and the easiest way of doing this was to use the old cable to pull through the two new ones.
What is worrying me is how many mains cables I have which are also next to these blocks and may be deteriorating in the same way. Is anyone aware of cables chemically reacting with building blocks?