Spotted from the train on the way to Cologne. 13 discs. Say diameter 15 cm and depth 4cm. Volume would be about 700 cubic cm. A search suggested a density of 2.4 grams per cubic centimetre for hardened concrete. That means each block would be 1.7 kg. The total stack would be 22 kg. That would be a force of about 200N. Is that enough? I need to look at the size of the wires next time. I think the blocks are concrete. If they were steel, the force would be nearly 4 times bigger.
