Explain the modified proctor test

The modified proctor test was developed to give a higher standard of compaction. This test was standardized by the American Association of state highway officials and is known as the modified AASHO test.

In this test, the mould used is the same as in the standard proctor test. However, the rammer used is much heavier and has a greater drop than that in the standard proctor test.  Its mass is about 4.89 kg and the free drop is 450 mm.  The face diameter is 50 mm as in the standard proctor test. The soil is compacted in 5 equal layers ,each layer is given 25 blows. The compactive effort in the modified proctor test is about 4.56 time than that in the standard proctor test. Thus, a much heavuer compaction is attained.

If the percentage of soil on a 4.75 mm sieve  is more than 20%, the larger mould of 150 mm internal diameter, effective height of 127.3 mm and capacity 2250 ml is used. In this case, 56 blows are required for each layer. The rest of the procedure is similar....

The modified proctor test was developed to give a higher standard of compaction. This test was standardized by the American Association of state highway officials and is known as the modified AASHO test.

In this test, the mould used is the same as in the standard proctor test. However, the rammer used is much heavier and has a greater drop than that in the standard proctor test.  Its mass is about 4.89 kg and the free drop is 450 mm.  The face diameter is 50 mm as in the standard proctor test. The soil is compacted in 5 equal layers ,each layer is given 25 blows. The compactive effort in the modified proctor test is about 4.56 time than that in the standard proctor test. Thus, a much heavuer compaction is attained.

If the percentage of soil on a 4.75 mm sieve  is more than 20%, the larger mould of 150 mm internal diameter, effective height of 127.3 mm and capacity 2250 ml is used. In this case, 56 blows are required for each layer. The rest of the procedure is similar to that in the standard proctor test.

The dry density is obtained for different water content and the compaction curve is drawn. Figure shows the compaction curve for the modified proctor test. The heavier Compaction increases the maximum dry density but decreases the optimum water content. The percentage increase of the dry density is between 3 % to 18% for most soils; the percentage increase is more for clayey soils than for the sandy soils.

Figure shows the zero air-void line. It may be noted that the maximum dry density attened even in the modified proctor test is lower than the theoretical maximum dry density indicated by the zero air-void lines. The line of optimum shown in the figure joins the points indicating the maximum dry density. It is roughly parallel to the zero air void line.