24 Aug 2017

HOW TO PERFORM COMPRESSIVE STRENGTH TEST OF CONCRETE (IS: 516)


COMPRESSIVE STRENGTH TEST OF CONCRETE (IS: 516)


the compressiove strength of concrete is the most common measured used by the engineers in degninig building and other structures. the compressive strength is measured by breaking cylindrical concrete specimens in compression testing machine. the compressive strength is calculated from the failure load divided by the cross sectional area resisting the load and reported in MPa in SI unit. concrete compressive strength requirement can very from 17 MPa for residential structure concrete to 28 MPa to higher for commercial sructures. higher strengths up to and exceeding 70 MPa are specified for certain application.


OBJECTIVE


To determine the compressive strength of concrete.


APPARATUS

  • Compression testing machine : (2000 KN/M2) Curing tank/Accelerated curing tank 
  • Balance : 0-10 Kg
  • Cylindrical mould : 150 mm diameter and 300 mm height
  • Cubical mould : 150 mm length 150 mm breath and 150mm height  6) 
Tempring rod : 16 mm diameter and 600 mm height 


MATERIALS


cement, fine aggregate(more than 50 % passes 4.75 IS sieve), course aggregate ( 1/4 the size of the cube, according to indian standard).



WATER-CEMENT RATIO



according to indian code of recommendation w/c ratio must be in the range of 0.42 to 0.60. for higher mix of concrete w/c ratio recommendation is 0.40 to 0.45.


CONCRETE MIX



M20 grade concrete mix is prepared for testing recommended by the indian standard for performing test to get best results.


PROCEDURE




  • Representative samples of concrete shall be taken and used for casting cubes 15 cm x 15 cm x 15 cm or cylindrical specimens of 15 cm dia x 30 cm long.
  • The concrete shall be filled into the moulds in layers approximately 5 cm deep. It would be distributed evenly and compacted either by vibration or by hand tamping.
After the top layer has been compacted, the surface of concrete shall be finished level with the top of the mould using a trowel; and covered with a glass plate to prevent evaporation.
  • The specimen shall be stored at site for 24+ ½ h under damp matting or sack. After that, the samples shall be stored in clean water at 27+20C; until the time of test. The ends of all cylindrical specimens that are not plane within 0.05 mm shall be capped.

  • Just prior to testing, the cylindrical specimen shall be capped with sulphur mixture comprising 3 parts sulphur to 1 part of inert filler such as fire clay.

  • Specimen shall be tested immediately on removal from water and while they are still in wet condition.

  • The bearing surface of the testing specimen shall be wiped clean and any loose material removed from the surface. In the case of cubes, the specimen shall be placed in the machine in such a manner that the load cube as cast, that is, not to the top and bottom.


  • Align the axis of the specimen with the steel platen, do not use any packing.


  • The load shall be applied slowly without shock and increased continuously at a rate of approximately 140 kg/sq.cm/min until the resistance of the specimen to the increased load breaks down and no greater load can be sustained. The maximum load applied to the specimen shall then be recorded and any unusual features noted at the time of failure brought out in the report.


CALCULATION


Compressive strength is calculate using the following formula


Compressive strength (kg/cm2) = W/ Ap
Where

Wf = Maximum applied load just before load, (kg)
Ap = Plan area of cube mould, (mm2)




1 comment:

  1. Its' really nice to read your blogs.

    Hi Guys, Please visit my Website and give me Suggestion.

    www.accrotech-testequipments.com

    ReplyDelete