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Table 15-4.-Recommended Slumps for Various Types of Construction Slump,  inches* Types  of  construction Maximum Minimum Reinforced  foundation  walls  and  footings Plain  footings,  caissons,  and  substructure  walls Reinforced  slabs,  beams,  and  walls Building  columns Pavements Heavy  mass  construction Bridge decks Sidewalks,  driveways,  and  slabs  on  ground 5 4 6 6 3 3 4 6 2 1 3 3 2 2 3 3 *When high-frequency vibrators are used, the values may be decreased approximately one-third; in  no  case  should  the  slump  exceed  6  inches. gradation;  specific  gravity,  absorption,  and  sur- face   moisture;    impurities,  such  as  organic material,  clay,  or  other  water-absorbing  particles; and  soundness,  which  is  the  property  of  an aggregate to resist disintegration due to freezing and thawing. Although these tests are not included in  this  TRAMAN,  you  may  refer  to  NAVFAC MO-330, Materials Testing,  should you desire to learn  more  about  them. Slump Tests As you are aware from your study of chapter 7,  WORKABILITY  is  the  relative  ease  or  diffi- cult  y  of  placing  and  consolidating  concrete.  When placed, all concrete should be as stiff as possible, yet maintain a homogeneous, voidless mass. Too much stiffness, however, makes it too difficult or impossible  to  work  the  concrete  into  the  forms and around reinforcing steel. On the other hand, too fluid a mixture is also detrimental. The mea- sure of the workability or consistency of concrete is its slump, which is a design consideration that is inversely proportional to the stiffness of the mix. As shown in table 15-4, the recommended values for slump vary for different types of construction. To measure slump, either during the preparation of  concrete  trial  batches  or  as  a  quality  control check during construction, testers perform slump tests. The procedures for performing slump tests will be explained later in this chapter. Strength  Tests In the design of concrete structures, the design engineer specifies given strengths that the final concrete  products  must  be  capable  of  attaining. When trial batches are prepared during mix design or as a quality control measure to ensure that con- crete  mixed  or  delivered  in  the  field  satisfies  those specified   strengths,   the   following   tests   are performed. COMPRESSION TEST.— Compression   tests are  conducted  to  determine  the  compressive strength  of  concrete  (or  its  ability  to  resist  a crushing force). In this test, a standard test load is  applied  parallel  to  the  longitudinal  axis  of  a premolded  and  properly  cured  concrete  cylinder of a standard size. When the testis properly con- ducted, a maximum load is obtained at the point at  which  the  cylinder  ruptures.  With  this  max- imum load, the compressive strength, measured in  pounds  per  square  inch  (psi),  can  be  easily calculated. Although the test procedures will be covered at the EA2 level, the procedures used to prepare  the  cylinders  for  testing  will  be  discussed later in this chapter. FLEXURAL STRENGTH TEST.—  The  flex- ural strength (modulus of rupture) test determines the flexural strength of concrete (or its ability to resist a breaking force). In this test, a standard 15-35



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