**What is characteristic strength (fck) of concrete mix design,****what is meant by fck in concrete,** in this topic we know about what is fck of concrete mix design and what is full form of fck in concrete. There is a need of know about value of characteristic compressive strength (fck) for every civil engineer or architect designer for building construction work.

When we calculate concrete and estimate value and design for theire project we need fck value of concrete.

**fck stand for (full form of fck) concrete**

Full form of fck is characteristics of compressive strength of grade of concrete and it is is measured in Newton per square mm (N/mm2) or mega pascal.

What is characteristic strength (fck) of concrete,We have different grade of concrete like **M20, m25, M30 ,m35 ,m40 ,m45 ,m50** and so more—-its meaning of following for example if we have M20 grade of concrete it means it has characteristics of compressive strength is about 20 N/mm2 and for **M 25 grade of concrete compressive strength is 25 N/mm2**

Grade of concrete are m5,m7.5,m10,m15,m20,m25 and m30 and fck value of concrete is 5N/mm2,7.5N/mm2, 10N/mm2, 15N/mm2, 20N/mm2, 25N/mm2 and 30N/mm2 respectively.

**compressive testing machine (CTM) for fck of concrete**

The characteristics of compressive strength of cube concrete can be tested with the help of compressive testing machine (CTM)in the laboratory.

In the test process of comprehensive strength of concrete cube suppose we have 100 concrete cube of M20 grade of concrete. All the concrete cube tested with compressive testing machine than following result is obtained

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**Test ,Rules and result of fck of concrete**

1) if 5% and less of concrete cube of M20 grade of concrete fail to withstand with compression pressure of 20N/mm2 in CTM machine in laboratory and 95% and more of concrete cube of M20 grade of concrete with stand with compression pressure of 20N/mm2 in CTM machine than it is called as successful of your test of concrete and their characteristics of comprehensive strength of M 20 grade of concrete is about 20 N/mm2

2) if more than 5% of concrete cube of M20 grade of concrete fail to withstand with compression pressure of 20N/mm2 in CTM machine in laboratory and less than 95% concrete cube of M20 grade of concrete with stand with compression pressure of 20N/mm2 in CTM machine than it is called as fail of your test of concrete and their characteristics of comprehensive strength of M 20 grade of concrete is less than 20 N/mm2.