Evidently, I've been doing this so long my brain has fried. I was reviewing the AASHTO T99/ T180 procedure.  I find the four methods described, but no indication of when to use a specific method, except the rather unhelpful,"If no method is specified, the provisions of method A shall govern"  Can anyone provide some guidance on when to use each of the four methods ( A-D)?
I know that ASTM D698/ 1557 has instructions for when to use each method, but they only have three methods, not the 4 of AASHTO.  I used to think that AASHTO and ASTM were identical on these tests, but it does not appear to be so.