The Proctor Compaction Test establishes the maximum unit weight that a particular type of soil can be compacted to using a controlled compactive force at optimum water content. the objective of this test is to obtain relationships between compacted dry density and soil moisture content, using two magnitudes of manual compactive effort. The test is used to provide a guide for specifications on field compaction.
The first is a light compaction test using a 2.5 kg rammer (Standard Proctor). The second is a heavy compaction test using a 4.5 kg rammer with a greater drop on thinner layers of soil (Modified Proctor). For both tests a compaction mould of 1 litre internal volume is used for soil in which all particles pass a 20 mm test sieve.
Method using 2.5 Kg rammer (BS Light)
Required equipment
• A cylindrical compaction mould with internal diameter of 105 mm and internal height of 115 mm and a volume of 1.0 L (1000 cm3). The mould shall be fitted with a detachable baseplate and a removable extension (collar) approximately 50 mm height.
• Subsidiary mould (CBR mould), diameter 152 mm, height 127 mm.
• A metal rammer having a 50 mm diameter circular face and weighing 2.5 kg. The rammer shall be equipped with an arrangement for controlling the height of drop to 300 mm.
• A balance readable to 1 g.
• Palette knives or spatulas
• A straightedge, e.g. a steel strip
• A 20 mm and 37.5 mm test sieves and receiver
• A container suitable for mixing the quantity of material to be used
• Water proof containers and scoop
• A large metal tray
• Measuring cylinder, 200 ml or 500 ml
• Suitable tools for extracting specimen from mould
• Apparatus for moisture content determination
Sample preparation
Prepare 5 representative samples each of about 3 kg of material passing the 20 mm test sieve. (For the use of the 1 litre mould). Break up lumps of fine material by rolling on a flat surface.
For coarser material where max. 10 % is retained on the 37.5 mm sieve and max. 30 % is retained on the 20 mm sieve, a CBR mould shall be used. The material coarser than 37.5 mm shall be removed and weighed, and replaced by the same quantity of material of the fraction 20 mm – 37.5 mm. In this case, each of the 5 samples should be of about 6 kg.
Mix each sample thoroughly with different amounts of water to give a suitable range of moisture contents. The range of moisture contents shall be such that at least 2 values lie either side of the optimum moisture content.
Seal each of the 5 portions in an airtight container and allow to cure for a minimum of 4 hours.
Test Procedure – 1 litre mould
- The mould with the base plate attached shall be weighed to the nearest 1 g (m1).
- Attach the extension collar and place the mould on a solid base, e.g. a concrete floor.
- Place a quantity of moist soil in the mould such that when compacted it occupies a little over 1/3 of the height of the mould body.
- Place the rammer with the guide on the material in the mould. Lift the rammer handle until it reaches the top of the guide, and then release the handle allowing dropping freely on the sample.
- Change the position of the guide and again drop the rammer. Repeat the process, systematically covering the entire surface of the sample. A total of 27 blows shall be applied.
- Remove the rammer and fill the next layer of soil in the mould, and repeat the above process twice more by applying 27 blows to both the second and the third layer. The mould should be filled, but the surface should not be more than 6 mm proud of the upper edge of the mould body.
- When all three layers are compacted, remove the extension collar, strike off excess soil and level the surface of the compacted soil to the top of the mould using the straightedge. Replace any coarse particles removed in the levelling process by finer material from the sample well pressed in.
- Weigh the soil and the mould with a baseplate attached to 1 g (m2).
- Remove the compacted sample from the mould. Take a representative sample of min. 300 g of the soil for determination of its moisture content.
- Discard the remainder of the sample. (The sample must not be re- used in a later test).
- This whole process shall be carried out for all 5 portions of the sample.
Calculations
1. Calculate the Bulk Density of each compacted specimen from the equation:
Where
m1 is the mass of mould and baseplate (in g)
m2 is the mass of mould, baseplate and compacted soil (in g)
V is the volume of the mould (in cm3)
2. Calculate the Dry Density, ρd (in kg/m3), of each
w is the moisture content of the soil (in %)
3. Plot the Dry Densities obtained from a series of determinations as ordinates against the corresponding Moisture Contents as abscissae. Draw a curve of best fit to the plotted points and identify the position of the maximum on this curve. Read off the values of dry density and moisture content, to three significant figures. The maximum may lie between two observed points, but when drawing the curve care should be taken not to exaggerate its peak.
Method using 4.5 kg rammer (BS Heavy)
In this test the compactive effort is greater than described in the above test. The mass of the rammer is increased to 4.5 kg, the height of the drop to 450 mm, and the number of compacted layers are increased from three to five.
The test is performed on material passing the 20 mm test sieve using the 1 L mould, or on material passing 37.5 mm test sieve using the CBR mould as described above.
The sample preparation and the testing procedure is identical to the above test with the exception of:
– The rammer used is 4.5 kg in weight with a drop of 450 mm.
– The moist soil shall be compacted in 5 equal layers into the mould
The number of blows applied to each layer shall be 27, i.e. the same as for the above-described test. Calculations, plotting of curves and expression of results including the test report are the same as for the above test.
References
The United Republic of Tanzania ministry of works, Laboratory Testing Manual 2000, Novum Grafisk AS, Skjetten Norway
