COMPRESSIVE STRENGHT by carthi

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   COMPRESSIVE STRENGHT OF
      HARDEN CONCRETE:


                               Objective:
To calculate the compressive strength

                              Introduction :

Result of testing concrete for strength is subject to
many variables . Concrete is made from different
material, by different method, and in different mix
proportion and is tested by different procedure .
Actually, these are all reasons why concrete must be
tested in a regular pattern during a job rather than
just once at the beginning .
The usual procedure is to cast test specimen as a
structure is placed, the measure of strength shown by
the test specimen is not a true picture of the concrete
strength. Test specimen are cured differently from
the structure and so do not reflect the workshop that
goes into the structure. The test is valuable as an

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approximation of actual strength, a test of potential
quality as delivered. Such tests keep batches of
concrete uniform throughout the job. Concrete is
usually proportioned for a given compressive
strength ( resistance to axial loading ) at a given age.
The test of compressive strength is one of the most
frequently used cylinder or cubes are taken and
tested at specified ages. Test specimens may show
different results depending on their moisture content,
the loading rate of the test apparatus, the test
temperature, lateral restraint, and many other
variables.
                                Standard :
B.S 1881 : PART3 : 1970
ASTM : C 39-72
        C 192-69
        C 470-76

                                Apparatus :

  •   Cube mould’s (15x15x15) cm .
  •   Compaction bar .
  •   Cylinders mould’s .
  •   Rod .
  •   Curing tank .
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                                Calculation :

 Sample no.
                                      1           2      3
Sample type
                       cube         cube        cube   cube
Age of sample
                       Days           7           7      7
  Sample’s
    length
                       mm            150         150    150
  Sample’s
     width
                         mm         150         150     150
  Sample’s
    height
                         mm         150         150     150
Sample cross-
 section area
                         cm2        225         225     225
  Sample’s
    volume
                         cm3        3375        3375   3375
   sample’s
    weight
                            g       6755        6749   6879
  Sample’s
    density
                       g/cm3        2.27        2.00   2.04
Crushing load
                      Kg          37716.62 35372.07 41284.40
Compressive
 strength
                     Kg/cm2        167.63   157.21   183.50

                Ave .compressive strength =169.45




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 Sample no.
                                    1          2          3
Sample type
                    cylinder    cylinder   cylinder   cylinder
Age of sample
                      Days          7          7          7
  Sample’s
    length
                      mm          150        150        150
  Sample’s
    height
                         mm       300        300        300
Sample cross-
 section area
                         cm2    176.71     176.71     176.71
  Sample’s
    volume
                         cm3    5301.44    5301.44    5301.44
   sample’s
    weight
                            g      -          -          -
  Sample’s
    density
                       g/cm3       -          -          -
Crushing load
                      Kg        23751.27 26095.82 19266.06
Compressive
 strength
                     Kg/cm2      134.41   147.68   109.03

          Ave .compressive strength =130.4
( ave.comp.st.cylinder )/( ave.comp.st.cube ) =
(130.4/169.45 )=0.77 ~ 0.8 relation .

                  Discussion and conclusion :
Compressive strength specimens are placed in an
apparatus that applies force on both ends until
failure.
Concrete is made from different material, also we
can tested it by different method.

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The number of strokes per layer required to produce
full compaction will vary according to the type of
concrete, but in no case shall it be less than 25 strokes
per layer .




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