Interesting subject wylk. I think a lot of the potential solutions would also be governed by balancing the mix ratios, without 'over-filling' the concrete with too much solids or additives.
In the same way the balance is critical using steel reinforcements, spiral, mattresses, rebar etc it all has to be right in order to prevent oversteeling of the concrete.

The carbon fibre idea is one I've pondered over for a long time. Can't help thinking that it might have a lot of potential uses for safe and vault protection, I'm surprised that we don't hear more mention of it, especially with German manufacturers like Stacke.

Not sure about the diamond dust idea, think dust might act more like a mild polishing abrasive, it'd need to be gritty chips of material like those deposited on coarse files and rasps in order to be most effective.
The big problem with diamond coating anything for vault walls is you need a lot of it because of the massive surface areas involved.
I'm sure that if internal reinforcements had an electro-deposited diamond coating it would be highly effective against the core drill, albeit costing more than the rest of the vault put together!

i think the combined use of hard and soft materials to choke and clog cutting tools is an often overlooked one. I experimented years ago and found that a particularly soft and 'sticky' grade of aluminium alloy 'seeded' with Ball bearings gave reasonable resistance against even the fiercest disc-cutter. Once the disc choked with the soft alloy it became largely ineffective. Perhaps Soft plastic inserts or epoxy resins could be used as a cheap way of achieving similar in a concrete matrix, it all helps to buy that bit of extra time.

safeman, your mention of Tann's use of ball bearings reminded me of a Tann Bankers I opened years ago, was early 1960s model I think, with chrome trim and two brass 10-lever locks. Think I put one hole through the side into the bolt case and 2 through the front over the locks(4 and a half inch door slab from memory) and can remember clearly both door and body had loads of tiny ball bearings in the mix. Perhaps this was similar to their vault panels idea? Was simple but effective, I wasn't using a core drill but it was tough stuff and frequently chipped the cutting edges of the TC tipped drills. anyway I've lost this a few times now and managed to bring it back so time to go before I lose the entire lot, happy new year everyone :-)