Differences in Breaching Charges: What does that mean?

[mmartin798]

For an encounter group I am making for my game, I needed to get some stats for a 90mm gun round. The penetration listed for it is "8 inches of double-reinforced concrete". This shouldn't be a problem, just look up the breaching charge for that and done. But here is the problem I have. In 4ed, the listing just says reinforced concrete, just like in the 3rd edition. But when you look at the amount of C4 for breaching, the 4ed amounts are about double the 3rd edition amounts all the way up the scale. The same is true for armor value of reinforced concrete between the editions. This could be because of the increased use of double-reinforced concrete between the publication of the two editions.

Now I am not a civil engineer, but I do know my physics. I now know what the difference between single and double-reinforced concrete is, but I can't find a relatively simple answer to a naive question. That being is double reinforced concrete basically twice as resistant to breaching as single reinforced concrete? I really don't want to look up a bunch of physical properties of concrete and steel to do the calculations myself. The answer doesn't even need to be exact. I just want a ballpark, bar napkin approximation of the relative strength. Does anyone here know the answer for the sake of my sanity?