**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.

Contents:

**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**

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.

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.

**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**

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

**Sampling of Cubes for Test**

- Clean the mounds and apply oil.
- Fill the concrete in the molds in layers approximately 5 cm thick.
- 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).
- 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**

- Remove the specimen from the water after specified curing time and wipe out excess water from the surface.
- Take the dimension of the specimen to the nearest 0.2m
- Clean the bearing surface of the testing machine
- Place the specimen in the machine in such a manner that the load shall be applied to the opposite sides of the cube cast.
- Align the specimen centrally on the base plate of the machine.
- Rotate the movable portion gently by hand so that it touches the top surface of the specimen.
- Apply the load gradually without shock and continuously at the rate of 140 kg/cm
^{2}/minute till the specimen fails - 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 cm^{2}

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 mm^{2)}=……………N/mm^{2}

=……………………….N/mm^{2}

**Reports of Cube Test**

- Identification mark
- Date of test
- Age of specimen
- Curing conditions, including date of manufacture of specimen
- 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/ mm^{2} (at 7 days)

Average compressive strength of the concrete cube =………. N/mm^{2} (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.

Age | Strength percent |

1 day | 16% |

3 days | 40% |

7 days | 65% |

14 days | 90% |

28 days | 99% |

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

Grade of Concrete | Minimum compressive strength N/mm^{2} at 7 days | Specified characteristic compressive strength (N/mm^{2}) at 28 days |

M15 | 10 | 15 |

M20 | 13.5 | 20 |

M25 | 17 | 25 |

M30 | 20 | 30 |

M35 | 23.5 | 35 |

M40 | 27 | 40 |

M45 | 30 | 45 |

**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:**

## Ashar

How can I download the file to my mobile phone

Useful for us..

This test shows 1st step of strength of concrete.

So its important to us……

SO HELPFUL 2 CIVIL ENGINEERZ

clarity blend with simplification,….quite rare

thanks

Hai very use full infermation

good info.

very nice

very useful thank u

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

PLZ SEND MORE INFORMATION ABOUT CIVIL ENGG

nice

good information to fresh civil engineers …..

Nice Topic

verry verry useful for quality.

thanks…………….

very very useful to every civil engineer…

very useful information

This is correct site to learn

Really thanks to help engineers by this address.

thanks for information

like it

hello you as a quality civil

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

refreshment text for all civil Engineers..

Very good subject, we learnt a lot of lesson

its really a benifishial

how much concrete tem winter help me

Very important test

most use full for all related with construction

I really like this site! Very informative and resourceful.

good………….this note I looking for long time………….

Excellent information

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..:)

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

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

which IS code is used to testing concrete cylinder specimen?

if u now that p ans me.

I might use this as my final year project hehehe.

good for use.

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

post some important material test.

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

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

what should be the average speed of needle?

useful notes

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

thanks its very useful for me.

what to do if Concrete compressive strength fails?

yes it will. it may increase the strength …

I dont know.. bt i never seen more than 50 MPA….n ma experience

sir actually i think it is 5N/sec

khup chan

5m3(cubic metres means what amount eg of stones.

Really nice specification…..

thank you..

@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.

this has been good for me in my field work.

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

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

its good for us.

what is the max stress for the road concrete according to BS?

we realy need this limits thanks.

factors affecting the strength of concrete.

hai daddy

This has made my report alot easier..

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?

I like this.This is worth reading.I like my profession.

what about machine mixing.

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

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.

Thanks for the info :) dude.

it can useful in psc exam.

This is my final year project! Very funny.

why reinforce concrete is 1:2:4 but not 1:3:6.

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

good

thanks

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

yes

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

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

hi guys i'm doing in GBFS in replacement with fine aggregate can u tell me the values after curing fro 3,7,28 days………………

nice

how to convert 5.2kn/s to140kg/cm2/min.

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

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

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

kevvu keka

why we must place some grease into the mould?

so the sand we fill in it does not stick to the mold and can be easily taken out and wighted

cuz we don't want the concrete to stick inside the mold

not grease only shuttering oil and why because by oiling the cubes can easily out from cube mould.

because the concrete should not stick to the mould surface and it can be easily demould

very nice

will the strength of 26 days be different from that of 28 days?

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

kindly refer IS-516 for more details………

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

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?

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

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

at 7 day you will get probably 80% of your target strength

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

Mama over quality person aitiya da?

will effect also if the water temperature decrease and be careful from salty water

hey pradeep ,it will also increase the cube strength

Yes

How much increased the temperature of water in curing tank sir ?

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

nice post Mr. gopal

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

What would be the earliest time to start curing of a slab.

10 hrs.

Very useful

thanks. helpful!

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

Thanks, and I need notes about concrete technology books.

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.

nice post

mana compressive strength korang hah?

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>.

what is the standard value of slump test

## Gopal Mishra

values of slump test depends on the type of work.. refer to the link below for standard values of slump tests for different works.

Slump Test & Its Valuesthanks

How many cube samples should be taken ?

## Gopal Mishra

read the reply to your earlier comment just above.

Hi Mr Gopal

How many cube samples should be taken ?

If i m pouring 100m3 of concrete

## Gopal Mishra

It depends upon the specifications of the client for whom you work. Generally, you can take 3 cube samples per 20 m3 of concrete.

mr. Gopal

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

## Gopal Mishra

you can use cylinder or cube for testing. We generally use cubes in India, may be at your place, you use cylinders for testing. But in India, we define strength as strength of cube after 28 days of casting. So we prefer cubes.

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 .

## Gopal Mishra

There can be many problems like thorough mixing of concrete, compaction, cement content, water content, size of aggregates etc. These are the main things to consider while mixing concrete. Also, transporting and placing can be a problem, as segregation can take place during transporting and placing. If you take care of your mixing, cement content, aggregate size proportion, water content, compaction etc, you will get good strength concrete.

Prabhat, Can specify the content you took for mixing-i.e cement,aggragate,sand,water, admixture

dear sir,

one thing iam not understanding i.e why concrete cube size is 150*150*150mm

not 200mm. please reply me asap.

## Gopal Mishra

cube size is 150x150x150, because it has been set as standard size, the value of compressive strength of which has been standardized at 28 days.We can also use 200mm cube, but you have to convert the compressive strength of 200mm cube to the equivalent of 150mm cube to know the actual strength of the concrete.

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

” need the answer ”

## Gopal Mishra

when you test a number of standard cube and a number of standard cylinderical specimen of concrete, and draw the normal distribution curve and then calculate the characteristic strength from cube and from cylinder, you will find the followingFck(cube) = 1.25 Fck (cylinder)=> Fck of cylinder = 0.8 Fck (cube)

Fck being characteristic strength.

This relation has been obtained from number of tests done on different samples.

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 ?

## Gopal Mishra

15 cm is the standard mould size and based on that only we get the actual strength of concrete after testing. You can use 10 cm mould, but you should be able to convert the strength values corresponding to 15 cm mould (std mould).

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

means that the strength of curing period??

## Gopal Mishra

actually, for precast concrete, members should attain minimum strength for handling and transportation. that minimum strength is calculated based on many factors.

The minimum concrete strength will be based on the calculated concrete stresses at the lifting points, or on calculated stresses caused by the transfer of

prestressing forces or handling. Curing period as I have said earlier is not correct.

actually, for precast concrete, members should attain minimum strength for handling and transportation. that minimum strength is calculated based on many factors.

my question: can u list to me the factors of minimum strength??

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

## Gopal Mishra

if top surface of cylinder is rough, then the stress distribution is not uniform over the surface. Then it depends on the amount of roughness.

very usefull

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

sir,

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

What machine is used to measure the same?

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).

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)?.-Ans:-..The Crack point is the point of failure/breaking point..

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

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

## Gopal Mishra

for M20 grade, minimum strength should be 20N/mm2. If its not achieved, then concrete is rejected. Normally for M20, strength you should get is more than 25 N/mm2 for nominal mix concrete if good quality control is achieved.

thanx 4 helping me in completing my work

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

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

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

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.

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

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.

Hi Gopal Ji,

What is the minimum L/d ratio required for conducting low strain pile integrity test.

Thanks

Nitin K.

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

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

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.

## Gopal Mishra

Hi Nitin,

As per my knowledge, IS Code does not specify 3, 7 and 14 days strength. But it only says 28 days strength.

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 ?

## Gopal Mishra

take minimum 6 cubes… 3 cubes for 7 days strength and 3 for 28 days…

Why we are testing concrete cubes after 7,14 or 28 days, why not 2,5,20 days.

## Gopal Mishra

we are testing week wise… 1 week, 2 week, 3 week etc. Standard test results were formatted on these days 7 days, 14 days, 28 days etc. We can plot a graph and can find the relative strength on 1 day, 2 day or 20 days also..

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

## Gopal Mishra

read answer to first comment on this page..

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

dear sir,

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

dear sir,

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

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

Thank you.

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

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

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?