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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. Sample type Age of sample Sample’s length Sample’s width Sample’s height Sample crosssection area Sample’s volume sample’s weight Sample’s density Crushing load Compressive strength
cube Days mm mm mm cm2 cm3 g g/cm3 Kg Kg/cm2
1 cube 7 150 150 150 225 3375 6755 2.27
2 cube 7 150 150 150 225 3375 6749 2.00
3 cube 7 150 150 150 225 3375 6879 2.04
37716.62 35372.07 41284.40 167.63 157.21 183.50
Ave .compressive strength =169.45
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Sample no. Sample type Age of sample Sample’s length Sample’s height Sample crosssection area Sample’s volume sample’s weight Sample’s density Crushing load Compressive strength
cylinder Days mm mm cm2 cm3 g g/cm3 Kg Kg/cm2
1 cylinder 7 150 300 176.71 5301.44 -
2 cylinder 7 150 300 176.71 5301.44 -
3 cylinder 7 150 300 176.71 5301.44 -
23751.27 26095.82 19266.06 134.41 147.68 109.03
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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