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Why do We Test Concrete Compressive Strength after 28 Days?

Strength of concrete is generally tested after 28 days as concrete cube strength or concrete cylinder strength. The reason for testing concrete strength after 28 days is discussed.

Why do we test concrete compressive strength after 28 days?

Concrete gains strength with time after casting. It takes much time for concrete to gain 100% strength and the time for same is still unknown. The rate of gain of concrete compressive strength in higher during the first 28 days of casting and then it slows down.

The table below shows the compressive strength gained by concrete after 1, 3, 7, 14 and 28 days with respect to the grade of concrete we use.

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

From above table, we see that, concrete gains 16 percent strength in one day, 40 percent in 3 days, 65% in 7 days, 90% in 14 days and 99% strength in 28 days.

Thus, it is clear that concrete gains its strength rapidly in the initial days after casting, i.e. 90% in only 14 days. When, its strength have reached 99% in 28 days, still concrete continues to gain strength after that period, but that rate of gain in compressive strength is very less compared to that in 28 days.

compressive-strength-test-on-concrete-cubes

After 14 days of casting concrete, concrete gains only 9% in next 14 days. So, rate of gain of strength decreases. We have no clear idea upto when the concrete gains the strength, 1 year or 2 year, but it is assumed that concrete may gain its final strength after 1 year.

So, since the concrete strength is 99% at 28 days, it’s almost close to its final strength, thus we rely upon the results of compressive strength test after 28 days and use this strength as the base for our design and evaluation.

Though there are also some rapid method of testing concrete compressive strength which gives relation between rapid test methods and 28 day strength. This rapid test is done where time is limited for construction and strength of structural member must be known to carry out further construction work.

Read More:

Concrete – Definition, Grades, Components, Manufacture, Construction and Articles

Compressive Strength of Concrete Cubes

Planning In-Situ Testing of Concrete for Strength, Durability and Damages

About Gopal Mishra

Gopal Mishra is a Civil Engineer from NIT Calicut and has more than 9 years of experience in Civil Engineering and Construction. He is the founder of The Constructor.

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Comments ( 32 )

  1. Because in 28 Day concrete gain 100% Strength as per grade

  2. No need to demolish so many ways like injecting chemical in concrete and jacketing are the ways to given sttrngth. Gp2 Is the well known chemical..

  3. There are construction practices that the foundation is being poured directly into the earth. For your plot with high level of salty water, you may provide a lean concrete min of 4" before your foundation . Making sure also that your concrete cover for reinforcements is being observed with proper concrete spacer. Insufficient concrete cover can affect the bar reinforcement on the "salty" environment. Controls during concrete pouring must be observed since actual scenario – it is being neglected

  4. sir thanks for your information but percentage you are given it have any reference or any recommendation by ASTM standard

  5. Do these tabulated data belong to any references or any recommendations by codes?

  6. I really appreciate this information, I will like to have more

  7. how about for non load bearing material that use some cement e.g wood wool cement board. Do we need to wait until day 28 for test? TQ

  8. but it totally depend upon curing

  9. It is mostly useful to all field engineers and helps them

  10. and last 1% …?????

  11. Chandragasan Chandrasekar
    Aug 14, 2014 at 08:34

    u r right

  12. We test the concrete after 7 days or 14 days and mostly 28 days, if test results are negative then what?

  13. thanks for this information but i have a question on the plot that consists salt what what precaution shall i take for better design and sustainable building structure

  14. How about accelerated curing/steam curing and the testing details? Please throw light on this.

  15. Actually modern day concrete give more strength in early age. As an example I have experienced 80% of strength achieving within 7days without any admixtures.

  16. May be every er. Knows!
    But simple explanation. That's Why I like Constructor.org very much since long before. Thanks for your valuable articles!

  17. The knowledge of:
    WHY WE TEST CONCRETE SRTRENGTH AFTER 28 DAYS?

  18. Tankx for your agkwn……

  19. What is the importance of NDT test???? And what is the latest technology of NDT to make easy and simple?

  20. because its necessity of now days .and we check the quality of mixing concrete

  21. AFTER HOW MANY DAYS OF CASTING CONCRETE IS TREATED AS OLD CONCRETE

  22. For required strength concrete must be mixed properly & ratio of cement & water cement ratio be maintained, curing should be done atleast for seven days

  23. varun im raju kc from nepal plz contg me

  24. what is the formula as per is code to test concrete after 30 days and what percentage difference do we get?

  25. what if the cube set failed in test? will you demolish the whole structure? but you can't wait for 28 days after casting you have to do simultaneously the other casting also.

    • you do not have to demolish the structure before carrying out a core test to determine the insitu strength of the dried concrete

  26. bagus…utk infomasi kita semua.

  27. 100 Years Durability Possible in Prestressed Concrete Products, for Ex. Prestressed Concrete Spun Poles.
    for more details log on http://manchukonda.com.

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