The Proctor test (ASTM D698 standard, ASTM D1557 modified) is a laboratory test that determines the maximum dry density and optimum moisture content of a soil. Field compaction results are expressed as a percentage of the Proctor maximum — a spec calling for "95% compaction" means the in-place dry density must reach 95% of the lab Proctor value. The Proctor curve for each soil type on site is the reference every field density test is judged against.
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