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.
Soil compaction and density testing are two of the most common and important soils tests that an EA must learn to perform. Those tests, as well as the California bearing ratio test and hydrometer analysis, are discussed in this section.
COMPACTION TEST 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. Equipment 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
Figure 13-4.—Sand-displacement method apparatus. required that 98 percent of the maximum density be not within the specified range, additional rolling may be obtained through compaction. The maximum attainable was 127.2 pcf; 98 percent of this is 124.7 pcf. The dotted line is drawn at the 124.7 pcf level. Any moisture content lying in the crosshatched area above this line would produce the specified density for a given compactive effort; therefore, the range of permissible moisture content is from 9 to 13 percent.
DENSITY TESTS From the preceding discussion, you know that compaction testing is performed to determine the OMC and the maximum density that can be obtained for a given soil at a given compactive effort. You also know that, using the maximum density, you can determine a range of densities and moisture contents that will satisfy the compaction requirements for a project. During the construction of that project, however, a control must be in place to measure whether or not the compaction requirements have been met. That control is density testing. If the results of the density test determine that the compaction process has produced a density within the range specified, then the compaction is complete. On the other hand, if the test results reflect densities that are necessary or the moisture content may have to be adjusted. Several different methods are used to determine the in-place density of a soil; however, the methods that EAs are most apt to use are the sand-displacement method and the nuclear moisture-density meter method. Sand-Displacement Method A full discussion of the procedures used in the sand-displacement method can be found in
Test Method for Pavement Subgrade, Subbase, and Base-Course Material, MIL-STD-621A, and in NAVFAC MO-330. This method, often called the sand-cone method, may be used for both fine-grained and coarse-grained materials. In general, the test consists of digging out a sample of the material to be tested, using calibrated sand to determine the volume of the hole from which the sample was removed and to determine the dry unit weight of the sample.