As you know by now, materials testing is a major part of an EAs responsibilities, especially for those EAs assigned to the Seabee construction battalions. The EA3 TRAMAN introduced you to the subject of materials testing. In that TRAMAN, you learned many of the basic soils and concrete tests that an EA performs. This chapter furthers your knowledge of the subject area.

In this chapter you will be introduced to several soils tests that the EA2 is expected to perform. You will study the constituent ingredients used in the production of concrete and will be introduced to many different procedures for testing those ingredients. You will learn about the tests used for concrete mixture design purposes and for determining the strength of concrete. Also, you will study bituminous materials, learn about methods used to test those materials, and will be introduced to various tests used in the design of bituminous pavement mixtures.

Although some of the tests discussed in this chapter are covered in seemingly thorough detail, it is not the intent of this TRAMAN to teach you how to perform the tests; instead, you will learn the purpose and principles of the tests, but only the fundamental procedures. For each test, the discussion identifies an authoritative source that you should refer to for detailed procedural guidance. Always use those sources when actually performing any of the materials tests.

Compaction is the process of increasing the density (amount of solids per unit volume) of soil by mechanical means to improve such soil properties as strength, permeability, and compressibility. Compaction is a standard procedure used in the construction of earth structures, such as embankments, subgrades, and bases for road and airfield pavement.

In the field, compaction is accomplished by rolling or tamping the soil with special construction equipment. In the laboratory, compaction can be accomplished by the impact of hammer blows, vibration, static loading, or any other method that does not alter the water content of the soil. Usually, however, laboratory compaction is accomplished by placing the soil into a cylinder of known volume and dropping a tamper of known weight onto the soil from a known height for a given number of blows. The amount of work done to the soil per unit volume of soil is called compactive effort.

For most soils and for a given compactive effort, the density of the soil will increase to a certain point, as the moisture content is increased. That point is called the maximum density. After that point, the density will start to decrease with any further increase in moisture content. The moisture content at which maximum density occurs is called the optimum moisture content (OMC). Each compactive effort for a given soil has its own OMC. As the compactive effort is increased, the maximum density generally increases and the OMC decreases.

The following discussion briefly describes the equipment and procedures of the ASTM compaction test that determines the OMC and the maximum density obtainable under a given compactive effort. You can find a full discussion of the test in Materials Testing, NAVFAC MO-330.

The principal equipment used for the compaction test is the compaction cylinders and the compaction tamper that are shown in figure 13-1.

There are two compaction cylinders. The smaller cylinder (Proctor mold) is 4 inches in diameter and has a volume of 1/30 (0.0333) cubic feet. It is used for materials passing the No. 4 sieve. The Proctor mold is fitted with a detachable base plate and a removable extension collar that is 2 1/2 inches high.

Figure 13-1.Apparatus for soil compaction testing. 

The larger cylinder is the CBR mold. It is 6 inches in diameter, 7 inches high, and is fitted with a base plate and a 2-inch-high extension collar. When you are compacting a soil sample, a 2 1/2-inch-thick spacer disk is placed inside the CBR mold to control the thickness of the compacted sample. With the spacer disk in place, the volume of the mold is about 0.0735 cubic feet. The CBR mold is used for samples containing material retained on the No. 4 sieve.

The compaction tamper consists of a drop tamper in a cylindrical guide. The tamper has a drop weight that weighs 10 pounds and has a striking face that is 2 inches in diameter. The guide sleeve regulates the height of drop to 18 inches. To use the compaction tamper, you place the guide on top of the specimen and then draw the tamper to the top of the guide and allow it to drop.

Other items that you need to perform compaction testing are a balance or scale for weighing the material in grams, a 3/4-inch and a No. 4 sieve, moisture canisters, and tools, such as a mixing pan, spoon, trowel, spatula, and a steel straightedge for striking excess material from the top of the mold after compaction