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SOIL-CEMENT STABILIZATION - 14071_429
BITUMINOUS  STABILIZATION - 14071_431

Engineering Aid 2 - Intermediate Structural engineering guide book
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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







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