Quote Originally Posted by wylk View Post
Some types of rebar are epoxy coated, normally for corrosion resistance (not an expected issue for vaults). It might be possible to mix in a small amount of industrial diamond dust ("junk" diamond, even by industrial standards, if there is such a thing) into the epoxy. Alternatively, give the rebar a light coating of diamond then apply the epoxy or other coating to hold it in place until the concrete is poured. This might slow down a core drill enough to be useful. But it might also be excessively expensive in quantities that would do any good.

Some interesting ideas there wylk.

To add to these could be the method used successfully by Tann in their modular panels for demountable strongrooms way back in time.

They managed to achieve equivalent resistance times to 12" reinforced concrete in their 4" panels against the 100mm diamond core drill by the use of small (approx. 2mm.) ball bearings within the mix. The test results showed that as the dia.tube penetrated the concrete the balls began to accumulate around the cutting head groove causing some segments to break off causing the drill to seize.