MATERIALS TESTING

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.

SOILS TESTING

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 13-1.—Apparatus for soil compaction testing. fitted  with  a  detachable  base  plate  and  a  removable extension collar that is 2 1/2 inches high. 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. Sample Preparation and Compaction Procedures About   five   specimens,   containing   successively increasing     moisture     contents,     are     needed     to determine  the  OMC  at  which  the  maximum  density for  a  given  compactive  effort  will   occur.   For   the Proctor   mold,   about   6   pounds   for   each   specimen (about 30 pounds total) is needed. For the CBR mold, you will need about 12 to 14 pounds per specimen, or about 60 to 70 pounds total. Before the compacting begins, the sample is air- dried and a moisture content of the air-dried material is determined. Airdrying is done by spreading out the material in the sun or in front of an electric fan. The water content of the air-dried material is determined as  a  basis  for   estimating  the  amount  of  water  you need   to   add   to   each   trial   specimen.   The   driest specimen   should   contain   just   enough   water   to produce  a  damp  mixture  that  crumbles  readily.  For each succeeding specimen, increase the water content by about 2 percent until the wettest specimen is quite wet and plastic. The  compaction  procedures  for  nongravelly  and gravelly soils are the same with two exceptions. First, the 4-inch Proctor mold is used for fine-grained  soil, and the CBR mold is used for gravelly soil. Second, 25 tamper blows per layer are used for the Proctor mold, and  55  blows  per  layer  are  used  in  the  CBR  mold. That  results  in  equal  compactive  efforts  for  the  two mold sizes and soil volumes. To  compact  the  soil,  you  first  attach  the  base plate and collar to the mold. Then you fill the mold to the top of the collar with the material placed in five equal    layers,    compacting    each    layer    with    the appropriate 25 or 55 equally distributed blows. After compacting the

Figure 13-2.—Data sheet for soil compaction test. material, you remove the collar and weigh the mold and compacted   material.   Then   take   moisture   content samples from the top and bottom of the specimen and determine the moisture content for each. If the two moisture  contents  differ,  use  the  average  between them. A modification of the above procedure uses a 5 1/2-pound  tamper  and  the  material  is  placed  in  three equal layers, rather than five; otherwise, the test is the same. The procedures can be found in ASTM D 698. Data  and  Calculations Figure 13-2 shows the test results and calculations for a compaction test. As you can see, this test used a 10-pound tamper and Proctor mold. Five runs were made.  After  compaction,  the  weight  of  the  compacted soil and mold was recorded for each run. From this, the weight of the mold was subtracted to get the weight of the soil for each run. Then the wet unit weight was computed using the formula shown. Lines A, B, C, D, and E contain the data for the moisture-content  test  for  each  run.  Note  that  for  each run, there were two tests: one from the top of the mold and the other of soil from the bottom. The averages were  set  down  beside  average  moisture  content. Finally, the dry unit weight (density) in pounds per cubic  foot  (pcf)  for  each  run  was  calculated  by  the formula  shown.  As  you  can  see,  for  the  same compactive effort, the density varied with the average moisture  content. The ultimate objective of the compaction test is to determine the OMC; that is, the moisture content that yields maximum density for a given compactive effort

Figure  13-3.—Determination  of  optimum  moisture  content. You determine this by applying the test results to plot a the curve indicates that the maximum attainable density curve like the one shown in figure 13-3. for the given compactive effort was 127.2 pcf for which In this curve, the horizontal coordinates are the the OMC was 10.9 percent. average moisture contents; the vertical coordinates are The  dotted  line  marked  “98%  maximum  density” the dry densities. For the test results used in the example, indicates that, in this case, the project specifications

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.