Oven-dry and weigh the material retained. Then you can calculate  the  percentage  of  clay  lumps  and  friable particles using the following equation: Where: P   =   percent of clay lumps and friable particles w₁ =    original weight of test sample W₂ =    weight  of  retained  sample  after  wet sieving and drying Test for Undesirable Lightweight Material.— Soft, laminated pieces of aggregate, such as chert or shale, are harmful to concrete. Coal and lignite, also, are harmful and are distinguished from the lightweight materials by the brownish black or black color of the particles.  Visual  examination  of  the  coarse  aggregate will often show these minerals. The amount of these minerals  in  an  aggregate  can  be  determined  by submersing the aggregate in a liquid with a specific gravity that will allow the shale or other light particles to float and heavier particles to sink. For specific testing procedures, you should refer to ASTM  C  123  or  to  NAVFAC  MO-330.  Briefly,  you perform the test by first sieving the dried sample over a No. 50 sieve for fine aggregate and a No. 4 sieve for coarse  aggregate.  Weigh  the  sample  and  then  place  it into  a  heavy  liquid,  such  as  zinc  chloride  (specific gravity of 1.95 at 78°F). Agitate the mixture to allow the lightweight particles to rise to the surface and skim them off.  When  repeated  agitation  causes  no  further  particles to rise, you wash the sample in alcohol and then dry and weigh it. The percentage of undesirable, lightweight particles can then be calculated using the following formula: Where: L =   percentage  of  lightweight  material W₁ = dry weight of lightweight material W₂ = dry  weight  of  initial  sample  retained on No. 50 sieve for fine aggregate or No. 4 sieve for coarse aggregate Color Test for Organic Matter.— Any sand that gives  a  color  darker  than  the  standard  of  this  test probably contains an excess of organic matter that will reduce the strength of the concrete in which the sand is used. If you determine that organic matter is present, it is possible that it can be removed by washing; if not, better sand should be obtained. If neither of these things can  be  done,  it  will  be  necessary  to  use  a  lower water-cement  ratio  and  control  the  concrete  production carefully to obtain the desired strength. For the color test, you will need the items illustrated in figure 13-17. To perform the test, you add the sample being tested to a solution of sodium hydroxide and water. After allowing the sample to stand for 24 hours, you then compare the color of the liquid above the sample  to  a  standard  color  solution  consisting  of  tannic acid,  alcohol,  and  sodium  hydroxide.  If  the  liquid  above the sample is darker in color than the standard solution, the sand may contain organic impurities. NAVFAC MO-330 provides full details for preparing the solutions and performing the test. As an alternative, the color of the liquid above the sample can be compared with the colors given in the ASTM  standard  color  plate.  Then  decide  whether  the sand  contains  an  excessive  amount  of  organic  matter. SPECIFIC  GRAVITY,  ABSORPTION,  AND SURFACE  MOISTURE.—  These  tests  must  be performed  on  the  aggregate  before  the  necessary calculations can be made to design a concrete mixture. For  aggregates  used  in  portland  cement  concrete, measurements  are  made  to  determine  the  bulk  specific gravity of the aggregates in a saturated, surface-dry (SSD)  condition.  Specific  gravity  is  thus  based  on determining the total volume occupied by the aggregate particles,  including  the  permeable  pore  space. Absorption and surface moisture determinations are necessary to calculate the amount of mixing water used in a concrete mixture. Absorption, determined as a percentage,  represents  the  moisture  content  of  the aggregate when the aggregate is in a SSD condition. Surface moisture is the water that is present in both fine and coarse aggregate, exceeding that which corresponds to a SSD condition. Concrete-mixture  design  is  discussed  at  the  EA1 level in Part 2 of this TRAMAN. Specific  Gravity  and  Absorption,  Coarse Aggregate (ASTM C 127).— The summarized steps in determining the bulk specific gravity of SSD coarse 13-24