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The compressive strength of the concrete cube test provides an idea about all the characteristics of concrete. By this single test one judge that whether Concreting has been done properly or not. Concrete compressive strength for general construction varies from 15 MPa (2200 psi) to 30 MPa (4400 psi) and higher in commercial and industrial structures.

Compressive strength of concrete depends on many factors such as water-cement ratio, cement strength, quality of concrete material, quality control during the production of concrete, etc.

Test for compressive strength is carried out either on a cube or cylinder. Various standard codes recommend a concrete cylinder or concrete cube as the standard specimen for the test. American Society for Testing Materials ASTM C39/C39M provides Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens.

Compressive Strength Definition

Compressive strength is the ability of material or structure to carry the loads on its surface without any crack or deflection. A material under compression tends to reduce the size, while in tension, size elongates.

Compressive Strength Formula

Compressive strength formula for any material is the load applied at the point of failure to the cross-section area of the face on which load was applied.

Compressive Strength = Load / Cross-sectional Area

Procedure: Compressive Strength Test of Concrete Cubes

concrete cube mould

For cube test two types of specimens either cubes of 15cm X 15cm X 15cm or 10cm X 10cm x 10cm depending upon the size of aggregate are used. For most of the works cubical molds of size 15cm x 15cm x 15cm are commonly used.

This concrete is poured in the mold and appropriately tempered so as not to have any voids. After 24 hours, molds are removed, and test specimens are put in water for curing. The top surface of these specimen should be made even and smooth. This is done by placing cement paste and spreading smoothly on the whole area of the specimen.

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These specimens are tested by compression testing machine after seven days curing or 28 days curing. Load should be applied gradually at the rate of 140 kg/cm2 per minute till the Specimens fails. Load at the failure divided by area of specimen gives the compressive strength of concrete.

Compressive Strength Test on Concrete Cube

Following are the procedure for testing the Compressive strength  of Concrete Cubes

Apparatus for Concrete Cube Test

Compression testing machine

Preparation of Concrete Cube Specimen

The proportion and material for making these test specimens are from the same concrete used in the field.

Specimen

6 cubes of 15 cm size Mix. M15 or above

Mixing of Concrete for Cube Test

Mix the concrete either by hand or in a laboratory batch mixer

Hand Mixing

  1. Mix the cement and fine aggregate on a watertight none-absorbent platform until the mixture is thoroughly blended and is of uniform color.
  2. Add the coarse aggregate and mix with cement and fine aggregate until the coarse aggregate is uniformly distributed throughout the batch.
  3. Add water and mix it until the concrete appears to be homogeneous and of the desired consistency.

Sampling of Cubes for Test

  1. Clean the mounds and apply oil.
  2. Fill the concrete in the molds in layers approximately 5 cm thick.
  3. Compact each layer with not less than 35 strokes per layer using a tamping rod (steel bar 16mm diameter and 60cm long, bullet-pointed at lower end).
  4. Level the top surface and smoothen it with a trowel.

Curing of Cubes

The test specimens are stored in moist air for 24 hours and after this period the specimens are marked and removed from the molds and kept submerged in clear freshwater until taken out prior to the test.

Precautions for Tests

The water for curing should be tested every 7 days and the temperature of the water must be at 27+-2oC.

Procedure for Concrete Cube Test

  1. Remove the specimen from the water after specified curing time and wipe out excess water from the surface.
  2. Take the dimension of the specimen to the nearest 0.2m
  3. Clean the bearing surface of the testing machine
  4. Place the specimen in the machine in such a manner that the load shall be applied to the opposite sides of the cube cast.
  5. Align the specimen centrally on the base plate of the machine.
  6. Rotate the movable portion gently by hand so that it touches the top surface of the specimen.
  7. Apply the load gradually without shock and continuously at the rate of 140 kg/cm2/minute till the specimen fails
  8. Record the maximum load and note any unusual features in the type of failure.

Note:

Minimum three specimens should be tested at each selected age. If the strength of any specimen varies by more than 15 percent of average strength, the results of such specimens should be rejected. The average of three specimens gives the crushing strength of concrete. The strength requirements of concrete.

Calculations of Compressive Strength

Size of the cube =15cmx15cmx15cm

Area of the specimen (calculated from the mean size of the specimen )=225 cm2

Characteristic compressive strength(f ck)at 7 days =

Expected maximum load =fck x area x f.s

Range to be selected is …………………..

Similar calculation should be done for 28 day compressive strength

Maximum load applied =……….tones = ………….N

Compressive strength = (Load in N/ Area in mm2)=……………N/mm2

=……………………….N/mm2

Reports of Cube Test

  1. Identification mark
  2. Date of test
  3. Age of specimen
  4. Curing conditions, including date of manufacture of specimen
  5. Appearance of fractured faces of concrete and the type of fracture if they are unusual

Results of Concrete Cube Test

Average compressive strength of the concrete cube = ………….N/ mm2 (at 7 days)

Average compressive strength of the concrete cube =………. N/mm2 (at 28 days)

Compressive Strength of Concrete at Various Ages

The strength of concrete increases with age. The table shows the strength of concrete at different ages in comparison with the strength at 28 days after casting.

AgeStrength percent
1 day16%
3 days40%
7 days65%
14 days90%
28 days99%

Compressive Strength of Different Grades of Concrete at 7 and 28 Days

Grade of ConcreteMinimum compressive strength N/mm2 at 7 daysSpecified characteristic compressive strength (N/mm2) at 28 days
M151015
M2013.520
M251725
M302030
M3523.535
M402740
M453045

Some Facts on Concrete Strength Test

Why Compressive Strength Test of Concrete is Important?

The compressive strength of the concrete cube test provides an idea about all the characteristics of concrete. By this single test one judge that whether Concreting has been done properly or not.

What is compressive strength of commonly used concrete?

Concrete compressive strength for general construction varies from 15 MPa (2200 psi) to 30 MPa (4400 psi) and higher in commercial and industrial structures.

What is compressive strength after 7 days and 14 days?

Compressive strength achieved by concrete at 7 days is about 65% and at 14 days is about 90% of the target strength.

Which test is most suitable for concrete strength?

A concrete cube test or concrete cylinder test is generally carried out to assess the strength of concrete after 7 days, 14 days or 28 days of casting.

What is the size of concrete cubes used for testing?

For cube test two types of specimens either cubes of 15cm X 15cm X 15cm or 10cm X 10cm x 10cm depending upon the size of aggregate are used. For most of the works cubical molds of size 15cm x 15cm x 15cm are commonly used.

Which machine is used for concrete strength test?

The compression testing machine is used for testing the compressive strength of concrete.

What is the rate of loading on compression testing machine?

Load should be applied gradually at the rate of 140 kg/cm2 per minute till the Specimens fails.

Which ACI Code is use for Concrete Strength Test?

American Society for Testing Materials ASTM C39/C39M provides Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens.

Read More:

  1. Concrete – Definition, Grades, Components, Manufacture, Construction
  2. Why do We Test Concrete Compressive Strength after 28 Days?

Gopal Mishra

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189 Comments

  1. This test shows 1st step of strength of concrete.
    So its important to us……

  2. This site is very useful full of information serves as Guide book -CIVIL !!!

  3. site gives good information to the site engineers for accepting the concrete based on 7 days cube strength

  4. I really like this site! Very informative and resourceful.

  5. ya by seeing this I'm rembering my project… mine m35 vth rice huskash. but I'm nt findng jobs for civil please any one help me out…im instrented in site engineering..:)

  6. if the rate of loading is increased the strength achieved is more n If you apply the rate of loading still less u will get more strength which is not feasible hence the rate of loading shall b kept at constant rate as mentioned for further information u can refer properties of concrete by neveli

  7. it was really help full to know the strength of concrete at different ages
    n it was always confusion about testing of specimen that it should be tested after 7 , 14 … days of curing nt on de same day

  8. which IS code is used to testing concrete cylinder specimen?
    if u now that p ans me.

  9. PROCEURE (VII). 140kg/cm2/minute rate of increment by hand operated or electrical machine is not clear as per IS 516 (latest).

  10. what's the normal compressive strength of OPC cement in 28 days?

  11. really very very useful to every civil engineer…. thanks……

  12. Anyone knows the pace rate used for compressive strength test for 1000kg/m3 density of lightweight foam concrete?

  13. @zwa ryuny:These faces must be thinly coated with mould oil to prevent leakage during filling, and a similar oil film should be provided between the contact surfaces of the bottom of the mould and the base. The inside of the mould must also be oiled to prevent the concrete from sticking to it. The two sections must be bolted firmly together, and the moulds held down firmly on the base plates.

  14. percentage of strength attain in the stage of curing……….

  15. 1st good curing & quantity of cement, aggregate, sand, water & admixure then actual process of cube casting, so no chances of cube fail.

  16. In concrete compression test, normally 150mm x150mm x150mm concrete cube samples is used for testing. Why isn’t 100mm x100mm x100mm concrete cube samples used in the test instead of 150mmx150mmx150mm concrete cube samples?

  17. what if used are setting cement to make the concrete wont it set before.and stick to the walls.

  18. we using m40 to do 6 cubes for my customer, for its 28days cubes test result coming out is average 65.5n/mm , my customer ask me to give reason why cubes strength very abnormal.

  19. so the send we fiill in dstick the mould and can be easily taken out and weightedoes not.

  20. hi , can we use wet aggregate and wet sand to making concreet so the compressivestrength will be effect or not?

  21. wats the max compression strength achieved by M20 grade concrete @ 7 days & 28 days?

  22. need help in replacement of fine aggregate with copper slag. has anyone performed the research.

  23. how does amount of water affect on compressive strength?/.

  24. Dear sir my calculations says that it will take 1.43 minutes to fail M-20 concrete.

  25. can u guyz provide me the exact cube crushing strength % increment day by day up to 14 days.thnx.

  26. During testing of cubes, why is the marked face of cube always placed in front?

  27. please what will be the value of a mix concrete in a ratio of 1:2:4 and curing for 28 days.

  28. We casted Concrete Class 30/20 , and We are getting compressive strength of 28 days lower then 7 days suspected higher Sulphate Content it's other reason?

  29. Russell Barry Independent Materials Testing Brisbane Aust. May I ask which test method is referenced in this guide? Like the site – very useful thks.

  30. May I know what will be the cube breaking value for the 28 days, 14 days and 7 days curing of M20 concrete mix..

  31. If the temperature of water in curing tank of cube is increased, will it effect the strength of cubes…..

  32. cube results will vary and more deviation will found if rate of loading is differ.either pass or fail.

  33. Tamping rod is 1 inch sq.bar and not bullet pointed at lower end…..pl. conform?

  34. Rate of loading is kept uniform, preferably 140kg/cm2/min. If you calculate the same load on 15cm cube per second, it will be around 5.25kN/sec. The load on structure in actual case is not sudden, and impact strength and compressive strength differs, so we take some uniform loading on cubes, such that cube is tested compression but not impact. So, uniform load of 140kg/cm2/min is used which means 5.25kN/sec, i.e. a M20 concrete will fail in 5 to 6 seconds.

  35. I am looking for this article.. fortunately with your help I got it thanks for sharing..<a href="http://www.sourceinfratech.com">light weight bricks machinery manufcturers india</a>.

  36. Hi Mr Gopal

    How many cube samples should be taken ?
    If i m pouring 100m3 of concrete

  37. mr. Gopal
    i have confusion. cube gave more strength than cylinder. its ok. but why we use cylinder more or preferrabely in our constructions

  38. sir my 28 days cube test results  for M15 are very from 12n/mm2 to 30 N/mm2 what is the problem  in my volumetric mix .

  39. dear sir,
    one thing iam not understanding i.e why concrete cube size is 150*150*150mm
    not 200mm. please reply me asap.

  40. why a cylindrical concrete specimen has about 20 % strength less than the cubic concrete speciment ??

    ” need the answer ”

  41. Dear Sir, 
    I would like to know, for compressive strength measurement of cubes in which cement partially replaced with composites, can we use 10 cm mould? Is there a practical advantage of using 15 cm over 10 cm ?

  42. can u give me minimum ages for handling and transporting for precast concrete. which BS u follow???

  43. sir,if the top of the cylinder is rough,by how much is the compressive strength reduced?

  44. please mention acceptance criteria of cube testing after 28 days according to IS codes ?

  45. sir,
    Is adding admixtures to concrete changes the compressive strength ?if so which admixture will yield maximum compressive strength?and please mention their ratio?

  46. While assessing compressive strength of concrete by testing 150mmX150mm cube, shall we take stress at the point of failure noticed (in the form of crack) or allow the stressing till needle of dial gauge moves? Please indicate the relevant code (IS code, if available, would be preferable).

  47. why 2 samples of concrete cubes? why not 1 sample, why not 3 samples?

  48. SIR,FOR M-20 GRADE CONCRETE THE STRENGTH IS M-20 @ 28 DAYS, BUT IF @28DAYS THE STRENGTH ACHIVED IS LESS THAN 20 N/MM2 , THEN WOULD THE WHOLE CONCRETING IS REJECTED? , DOES THERE IS ANY CRITERIA FOR THIS PROBLEM

  49. please, i need a mathematical relationship between the compressive strength of concrete with respect to the days of curing.i’ll appreciate if i get it early,cos i need it for my project calculation.THANKS

  50. what is the conversion factor from 7days compressive strength to 28 days compressive strength of concrete.

  51. what is the conversion factor from 7days compressive strength to 28 days compressive strength of concrete.

  52. for a civil engineer, C25 means concrete having a compressive strength of 25Mpa but how can i explain this to someone who doesn’t know civil engineering.

  53. for cube of 150mm size and ram dia 165 mm and load is 600kn what is the compressive strength of concrete?

  54. Dear SIR,
                       will you please specify about the standard which says that 50 % is ok for concrete in 3 days compressive strength or any information on compressive strength of poly propylene fibre mixed concrete.in 3 days compressive strength . Regards Sooraj.

  55. Hi Gopal Ji,
    What is the minimum L/d ratio required for conducting low strain pile integrity test.
    Thanks
    Nitin K.

  56. sir how much strength we can achieve of concrete cube 15cm.

  57. what is the conversion factor from pounds per sq. mm to newton per sq. mm

  58. Mr. Gopal,
    Is there any specific required strenghth shown in/mention in IS or BS code.for example : for 3,7,14,and 28 days in percentage wise.

  59. Concrete slab (12 cm thick) of surface area of about 600 sq meter is to be cast with M20 concrete. Compressive strength is to be tested after 7 & 28 days. How many cube samples should be taken ?

  60. sir, what is the minimum and maximum compressive strength of concrete in 7 days of casting?

  61. What is the value of compressive strength of concrete according to CS I and/or I EN?

  62. dear sir,

    how many layer need to make cubes for compressive strength test according to BSEN standard, with s4 concrete

  63. dear sir,
    in how many layer need to make cubes for compressive strength test according to BSEN standard, concrete with s4

  64. What is the value of compressive strenght of concrete used for constructing roads in INDIA ?

    Thank you.

  65. Please i wish to know which elements should core and hammer test should carried being it,foundation,pedestal,roof or base foundation(lean concrete) or columms in accordance with BS standard or Specifications

    Thank you

  66. How can i carringout a project on effect of paint waste water on compressive strength of concrete.

  67. A cube of concrete is crushed to find its compressive strength. If the 150mm cube breaks at a load of 67.5 tonnes, what is its compressive strength?