Proctor Compaction Test

Published: July 23, 2020 | Last updated: July 5, 2023

What Does Proctor Compaction Test Mean?

The Proctor compaction test is performed to determine the maximum dry density of soil samples. It determines the optimal moisture content at which a given sample will become densest and achieve its maximum dry density.

The test is known as the Proctor compaction test in honor of Ralph Roscoe Proctor. In 1933, he showed that the dry density of soil for given compaction depends on the amount of water in the soil at the time of compaction.

The standard proctor test is detailed in ASTM D698 and AASHTO T99 test methods and the modified proctor test is detailed in ASTM D1557 and ASSHTO T180.


Trenchlesspedia Explains Proctor Compaction Test

The Proctor compaction test requires a compaction hammer to give the soil a certain number of blows from a predetermined height. Both the standard and modified test procedures are similar but the compaction hammer used in the two methods is different.

The compaction hammer used in the modified proctor test weighs 4.54 kg with an 18-inch free fall while the standard proctor test uses a hammer that weighs 2.49 kg with a 12-inch drop. These hammers are manually operated to compact the soil specimens into the compaction molds.

The modified proctor test is used along with the standard proctor test based on project requirements and specifications. In the test procedure, the prepared soil specimens with increasing moisture contents are compacted into molds of known volume. The molds are then weighed and their net weight are measured in pounds per cubic foot or kilograms per cubic meter.

The unit weights will increase as moisture content increases. The dry unit weight for each compaction cycle is calculated by correcting for the moisture content.

Results are plotted on a graph with the horizontal axis indicating moisture and the vertical axis indicating dry unit weight. The maximum dry density and optimum moisture content can be determined from the resultant curve.


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