Laboratory tests determine three fundamental control factors for soil-cement. These factors are as follows:

Obviously, it is important to sample and test the soils that will actually be used in soil-cement construction. A 75-pound sample of each type of soil is adequate for laboratory testing.

Sampling methods and procedures are discussed in the EA3 TRAMAN and in NAVFAC MO-330. Soil samples are usually taken from a graded roadway by digging a trench from the center line to the edge of the proposed pavement and to the depth of processing. Soil samples for proposed roadways not yet graded are taken with an auger from the various soil horizons of each soil type from the "dressed-down" face of exposed cuts or from the surface. Samples should be taken so that only one horizon of each soil type is represented by each exceptions. For instance, in sampling pit material that is to be loaded during construction by a shovel operating over the vertical face of the pit, the sample is taken from the bottom to the top of the vertical face after the overburden is removed. On small projects, it is not uncommon to sample only the poorest soil on the job, and the cement content for this sample is used throughout the job. Be sure that complete identification is supplied with each sample.

The purpose of laboratory testing is to determine the minimum cement content needed to harden the material adequately and the optimum moisture content (OMC) and density values to be used for construction. The OMC and maximum density are determined by the moisture-density test and the required cement content is determined by either the wet-dry test for pavements located in nonfrost areas or the freeze-thaw test for pavements located in frost areas. A brief description of each test is provided below.

. The moisture-density test determines the OMC and maximum density for molding laboratory specimens and, in the field, to determine the quantity of water to be added and the density to which the soil-cement mixture should be compacted. Before you start this test, select the cement contents that will be used in the wet-dry or freeze-thaw test. The cement contents are usually selected in 2-percent increments to encompass values given in table 18-3.

Since maximum density varies only slightly with variations in the cement content, only the median value is used in preparing specimens for the test. Additional information on selecting the cement content can be found in chapter 5 of NAVFAC MO-330.

The procedures for determining the OMC are similar to those described in chapter 13 of this TRAMAN with the following exceptions:

1. Compaction is performed on five layers of approximately equal thickness to result in a total compacted depth of 5 inches.

2. Each layer is compacted by 25 uniformly spaced blows using a 10-pound tamper dropped from a height of 18 inches.

. The wet-dry test (ASTM D 559) determines the cement content for soil-cement mixtures used in nonfrost areas. The objective is to determine the minimum amount of cement that will enable the soil-cement mixture to pass the test. For the test, specimens are molded using the OMC and the cement contents described above for different soil classifications. Use the procedure for the OMC determination to mold the specimens, and take a 750-gram sample from the second layer for a moisture determination. Cure the specimens for 7 days in high humidity. After curing, the specimens are weighed and submerged in tap water at room temperature for 5 hours. They are then oven-dried for 42 hours at 160F. Material loosened by wetting and drying is then removed using two firm strokes of a wire brush. After this, you then reweigh the specimens and subtract the new weight from the old weight to determine the amount of disintegration (soil-cement loss) that occurred during the cycle. The process is repeated for a total of 12 cycles. A passing grade ranges from 14-percent loss for sandy or gravelly soils down to 7 percent for clayey soil. Additional information about the wet-dry test and an example of determining the soil-cement loss can be found in NAVFAC MO-330.

. The freeze-thaw test (ASTM D 560) determines the cement content for soil-cement mixtures used in areas subject to frost action due to repeated freezing and thawing. As in the wet-dry test, the objective of the freeze-thaw test is to determine the minimum amount of cement that enables the mixture to pass the test. For the test, specimens are molded and cured in the same manner as the wet-dry test. After 7 days of curing, the specimens are placed on moist blotters and are refrigerated for 24 hours at -10F. They are then thawed in a moist atmosphere at 70F for 23 hours. Then you sharp-pointed instrument. After 12 cycles, the specimens are oven-dried and weighed. The soil-cement loss is determined the same way as in the wet-dry test. Again, passing grades range from 14-percent loss for sandy or gravelly soils down to 7 percent for clayey soil.

For additional information regarding the freeze-thaw test, you should refer to NAVFAC MO-330. The principal requirement of a hardened soil-cement mixture is to withstand exposure to the elements. Strength is a requirement also; however, most soil-cement mixtures that have adequate resistance to the elements also have adequate strength. In the ranges of cement contents producing results meeting the requirements above, the strength of soil-cement specimens tested in compression at various ages should increase with age and with increases in cement. A sample that has an unconfined compressive strength of approximately 300 pounds per square inch (psi) after curing 7 days and shows increasing strength with age can be considered adequately stabilized. NAVFAC MO-330 has the procedures that you should follow when performing unconfined compression tests.

For a discussion of modified mix design for sandy soils and for approximate and rapid test procedures that you can use when complete testing is impracticable, you should refer to NAVFAC MO-330. Construction methods using soil-cement can be found in Military, Soils Engineering, FM5-541, and in commercial publications, such as Moving the Earth, by Herbert L. Nichols, Jr., and various publications from the Portland Cement Association.