What Does Compaction Hammer Mean?
A compaction hammer is a tool used for the compaction of soil samples to determine their maximum dry density. The test used to determine this density is known as the Proctor compaction test, in honor of Ralph Roscoe Proctor. 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 test requires the compaction hammer to give the soil a certain number of blows from a predetermined height.
The compaction hammer is used in the proctor compaction test to make the soil dense and reduce air voids. The degree of soil compaction is measured in terms of its dry density. There are two types of test procedures, namely the standard Proctor test and the modified Proctor test. 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.
Both the 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. This allows for higher maximum soil density at lower optimum moisture content. 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.
A compaction hammer is also known as a proctor hammer
Trenchlesspedia Explains Compaction Hammer
Soil compaction is an important part of construction activities as it makes installations more permanent. Compaction increases the bearing capacity of the soil, helps reduce soil permeability, and controls erosion problems. Heaving and subsidence issues are also reduced.
Ralph R. Proctor established a laboratory procedure in 1933 when he was a student at the University of California, Berkeley. The test is known today as the standard Proctor test or moisture-density relationship test. Using the test procedure it is easy to determine the practical maximum density of a soil sample along with the optimum moisture content needed to achieve that density.
In the 1950s, a modified version of the test was introduced to accommodate testing for higher compaction. The test was based on the fact that the efficiency of soil compaction, especially that of cohesive soils is directly impacted by its moisture content. The standard Proctor test and the modified Proctor test have similar test procedures but the difference lies in the laboratory compaction effort used in the test.
The standard test includes a cylindrical mold with a volume of 0.95 liters in which the soil sample is compacted in three layers. Each layer is compressed using a 2.49 kg compaction hammer falling on the sample from a height of 12 inches or 30 cms, 25 times.
In the modified Proctor test, the cylindrical mold used is the same as for the standard test but the soil sample is compacted in five layers. The layers are compressed using a 4.54 kg compaction hammer dropped from a height of 18 inches or 45 cms, 25 times.
The Compaction Test
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 unit weight is 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.