I was reading my plumbing code and came across mysterious concrete classification numbers like C15 and C25.

I tried googling it and only came across a couple of sources describing these numbers (like here and here for example), but these sources do not appear authoritative.

Where can I find an authoritative description (preferably online) of these concrete classification numbers?

  • Try the American Society for Testing and Measures (ATSM.org). – ojait Nov 8 '15 at 16:25

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