A 570 switched from letters to numbered grades corresponding to yield point sometime in the late 70s or early 80s.

I *think* these are the correspondences, but some confirmation would be good:

letter  number  
  A       36 Type 2
  B       36 Type 1
  C       33
  D       30

A 1011 has the same grade numbers as A 570, so A 570 Grade C is probably A 1011 Grade 33.

Hg

Eng-Tips guidelines:  FAQ731-376

Thanks.

I also wrote to ASTM so with your info at least I can look for a specific revision year to find the change rather than each revision backwards from now until 1970.

--Scott

For some pleasure reading, try FAQ731-376

The change was before the 1985 edition.  Unfortunately my next earliest ASTM volume is 1965 and the spec didn't come out till 1966.  The Texas highway construction specs published in 1982 still have the letter references, but the change could have come before 1982 since (a) the publication date could be a couple years after the spec was written (b) they might not have looked at the very latest edition at the time.

Hg

Eng-Tips guidelines:  FAQ731-376

Thanks again for the help.  With your direction, we were able to narrow down the search and found the letter Grades to be in the 1972 edition of A570.  The next revision changed to number grades.

Comparing the 72 with 79 & 84a and 98 editions of A570:
72 -->  79 & 84a               --> 98
A   --> No direct comparison  --> NDC
B   --> 30                             --> 30
C   --> 33                             --> 33
     --> 36                             --> 36 Type 1
                                           --> 36 Type 2
D   --> 40                             --> 40
E   --> No direct comparison  --> NDC
     --> 45                             --> 45
     --> 50                             --> 50
                                           --> 55

--Scott

For some pleasure reading, try FAQ731-376