SOIL-CEMENT TESTS - 14071

gradation and absence of fines in these sands, construction equipment may have difficulty in obtaining traction. Traction can be vastly improved by keeping the sand wet and by using track-type equipment. These soils are likely to be “tender” and to require care during final packing and finishing so that a smooth, dense surface may be obtained. 3. Silty and clayey soils make satisfactory soil- cement but those containing high clay contents are harder to pulverize. Generally the more clayey the soil, the higher the cement content required to harden it adequately. Construction with these soils is more dependent on weather conditions. If the soil can be pulverized it is not too heavy textured for use in soil- cement. SOIL-CEMENT TESTS Laboratory tests determine three fundamental control factors for soil-cement. These factors are as follows: 1. Proper cement content 2. Proper moisture content 3. Roper density An adequate cement content is the first requisite for quality soil-cement. Well before construction, the soils at a project site should be identified, the limits of each soil defined, and a representative sample of each soil type should be forwarded to the laboratory to determine the quantity of cement required to harden it. A soil survey of the construction area should be made. Proper soil surveying, identification, and sampling are important. For instance, if one soil type was sampled and tested while actual construction involved a different soil type, the tests would be worthless and, in fact, detrimental since they would mislead the engineers. 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 sample. Similarly, it is not good practice to take a composite sample from various locations. Data obtained from a composite sample does not apply to soil in any single location and may be misleading. There are 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. Table 18-3.—Basic Range of Cement Requirements 18-6