Pyrites in concrete

Last year I had cause to learn about an activity new to me: mundic testing. As viewers of Poldark (1975) or Poldark (2015) or (more incidentally) Deadwood (2004) will know, Cornwall has a long history of mining, especially for copper and tin, separately from the current open-pit mining for kaolinite. Some of the mineral waste was included as aggregate in the concrete mixture for house construction but was later found to cause the concrete to degrade and crumble away. In those areas around the historic deep-shaft mines, testing for this condition has become routine for houses of a certain age. Unlucky house-sellers may thus discover that prospective buyers cannot secure a mortgage for the property.