In soil mechanics, the Proctor compaction test is one of the most important procedures for studying and quality control of soil compaction. Through it it is possible to determine the maximum dry density of a soil in relation to its degree of humidity, at a given compaction energy.

There are two types of standardized Proctor tests; the "Standard Proctor Test", and the "Modified Proctor Test". The difference between the two is found in the energy used, which is modified depending on the case by varying the number of blows, the tamper (changes height and weight), the mold and the number of layers. The reason there are two different essays is nothing more than the modernization of one with respect to the other. The origin of the Modified Proctor test dates back to the Second World War, when the Americans and British had to carry out tests on the quality of the pavements of airport works, and these had to be adapted to the airplanes of the time with a load much higher than that of land vehicles. For this reason, the Proctor test was “updated” by requiring a greater amount of energy, so the original was called the Standard Proctor test and the more recent one was called the Modified Proctor test.

Both tests are due to the engineer who gives them their name, Ralph R. Proctor") (1933), and determine the maximum density that can be achieved for soils, under certain conditions of humidity and energy.

The test consists of compacting a portion of soil in a cylinder with a known volume, varying the humidity to obtain the curve that relates the humidity and the maximum dry density to a certain compaction energy. The maximum point of this curve corresponds to the maximum dry density on the ordinate and the optimal humidity on the abscissa.

The compaction energy is given by the equation:.

Where:.

The degree of compaction of a soil is expressed as a percentage with respect to the Proctor test; That is, a compaction of 85% of Proctor Standard means that 85% of the maximum density of Proctor Standard is reached. The percentage may be greater than 100%, for example, in cases where the compaction energy in the field is greater than that of the Proctor Standard.

The main regulations that define these tests are the American standards ASTM D-698 (ASTM is the American Society for Testing Materials) for the standard Proctor test and ASTM D-1557 for the modified Proctor test. In Spain there are standards UNE 103-500-94 that defines the normal Proctor compaction test and UNE 103-501-94 that defines the modified Proctor test. In Argentina it can refer to the National Road regulations.