Comparison of Tests
The original Proctor test, ASTM D698 / AASHTO T99, uses a 4-inch-diameter (100 mm) mould which holds 1/30th cubic foot of soil, and calls for compaction of three separate lifts of soil using 25 blows by a 5.5 lb hammer falling 12 inches, for a compactive effort of 12,400 ft-lbf/ft³. The "Modified Proctor" test, ASTM D1557 / AASHTO T180, uses same mould, but uses a 10 lb. hammer falling through 18 inches, with 25 blows on each of five lifts, for a compactive effort of about 56,000 ft-lbf/ft³. Both tests allow the use of a larger mould, 6 inches in diameter and holding 1/13.333 ft³, if the soil or aggregate contains too large a proportion of gravel-sized particles to allow repeatability with the 4-inch mould. To ensure the same compactive effort, the number of blows per lift is increased to 56.
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