rubbish !..if so , how come 40mm paving slabs dont break all on their own ! lol
its all about mix strength, foundation prep and use of the material. Ralphie, you need to ask why the hole appeared in the first place...and that will determine how you repair it. If its a car / van wheel loading doing the damage, possibly no repair will last ... and what is the condition of the drive itself ...possibly it is unsuitable for the task in the first place etc...
concrete will crack at 40 times its thickness all by itself, so is this a factor ?Is the hole at the limit point of a large slab...as it could be the reason why it starts to crumble.
If a ground slab is well laid over a well prepared foundation, 100mm should be adequate for a 4m length without cracking .....but without knowing the base structure, loading and other conditions, its hard to say just what will last .