The "Modified Proctor" test, ASTM D1557 / AASHTO T180, uses same mould as the original proctor test, but uses a 4.54 kg. hammer falling through 457 mm, with 25 blows on each of five lifts, for a compactive effort of about 2700 kN-m/m3.
- Select a representative sample of sufficient quantity to perform the test; fine-grained soils require approximately 9000 grams taken from the portion of sample passing the 5.00 mm sieve coarse-grained soils require approximately 22 000 grams.
- Dry samples thoroughly in air or in the oven with a temperature not exceeding 600C.
- Break up aggregations, but do not crush individual particles.
- For fine-grained soils, separate material on the 5.00 mm sieve. Regrind the fraction retained and again separate on the 5.00 mm sieve. Repeat until grindings produce only a small quantity of material.
- Mix the fractions passing the 5.00 mm sieve thoroughly and use for the compaction test in the 101.6 mm mould.
- For coarse-grained soils, use all the material but replace particles retained on the 40.0 mm sieve with an equal weight of particles passing the 40.0 mm sieve and retained on the 18 mm sieve.
Test Procedures for Fine-Grained Soils
- Weigh out four 2200 g samples in separate mixing pans and label 1, 2, 3 and 4.
- Estimate the natural moisture content of the soil.
- Estimate the optimum moisture for the soil as well as the amounts of water
- Required to bracket the optimum. Strive for a spread of two percent in moisture content between samples with two samples below optimum and two above, as shown in the example.
Table 1 - Example Data Recording
Sample No 1 2 3 4 Sample Weight (g) 2200 2200 2200 2200 Natural moist. (est.)% 7 7 7 7 Optimum moist. (est.)% 15 15 15 15 Added water req’d. % 5 7 9 11 Total req’d. moist. % 12 14 16 18 Added water req’d. mL 110 154 198 242 Round off water req’d. mL 100 150 200 250
- Start the addition of water with sample No. 3, mix the required amount of water thoroughly with the soil and examine. If it is not over optimum moisture content, add additional water.
- Adjust the amount of water to be added to the remaining samples by an equal amount.
- If sample No. 3 (16% in the example) appears to be too far above optimum moisture when the required estimate of water is added, then it may be called sample No. 4. Reduce the quantity of water added to the other samples by an appropriate amount.
- Assemble the 101.6 mm mould with collar and base plate attached with insert Lucite liner. Place the assembly on the compaction base.
- Take the mixed sample and compact in the mould in five equal layers to give a total compacted depth of approximately 127 mm.
- Compact each layer with 25 blows from the rammer dropping freely from a height of 457 mm. Avoid bouncing the weight off the handle at the top of the stroke when operating the rammer. Distribute the blows uniformly over the surface of the layer being compacted.
- After the specimen has been compacted, remove the collar from the mould and use the straight-edge to trim the compacted soils even with the top.
- Remove the mould from the base plate, remove the compacted specimen and remove the liner.
- Weigh the specimen and record the weight to the nearest gram.
- Slice the sample vertically and remove approximately 100 grams of soil from the central section of the test specimen for moisture content determination. Place the sample in a tarred aluminium can, weigh, and oven dry to a constant weight at 110oC.
- Determine the difference between the wet and dry weights and record as weight of moisture for calculation of moisture content.
- Repeat the procedure for compacting and moisture content determinations for each of the four samples (i.e. two specimens below optimum moisture).
Test Procedure for Coarse-Grained Soils
The procedure to be used is similar to the procedure for fine-grained soil with the following exceptions:
- Weigh out four 5500 g samples.
- Compact the specimens in the 152.4 mm mold in five equal layers to give a total compacted depth of about 127 mm.
- Compact each layer with 56 blows from the rammer dropping freely from a height of 457 mm. Distribute the blows uniformly over the surface.
- Remove approximately 500 grams of material from the vertical central section of the test specimen for moisture content determination. Place this sample in a suitable pan and weigh.
- Carefully dry the moisture sample on a hot plate or oven at a temperature not exceeding 110oC.
- After cooling, weigh the pan and sample and determine the moisture content in a similar manner to that used for fine-grained soils.