Answer / viki

generally concrete attains 60-70% of its 28 days strength
in 7 days.After 28 days strength of M20 concrete will be
20N/mm2.so after 7days it would be 12-14 N/mm2.

Answer / dee

exactly 67% which is 13.7 n/mm2

Answer / n.c.pathan

Concrete does attain strength of about 65% after a period
of 7 days. With good quality of cement nowadays available
we generally get better results. Many a times strength
exceeds 70% of 20N/SQ MM.

Answer / g.mugesh

Grade of concrete:m20

7days test (67.5%) - 20*67.5/100=13.35 N/MM2
28days test(100%) - 20 N/MM2

Answer / himanshu sekhar pradhan

Actuall all grade of concrete design upon its target
strength. Then for M20 we have to design the mix on
26.6N/mm2 and all grade of concrete should achive its 60 -
75% strength in 7days. Then the actual strength of M20
grade of concrete at 7days should be 17 -20 N/mm2.
Otherwise there is chance of fail.

Answer / sumit

Design mix is M20 So Target strenth is Fck+4 = 24N/MM2

For 7 Days Cube strenth is 16.24 Exact (7days@67.67%)

For Individual Cube strenth become is Fck-3 = 13.24

But Average Sternth is required is 16.24 (must)

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Answer / sathish

Actually concrete attains 64-70% of its 28 days strength
in 7 days.After 28 days strength of M20 concrete will be
20N/mm2.so after 7days it would be 12.80 -14.00 N/mm2.

Answer / nithin

Is there any reference to 7 day strength in is codes.

Answer / sandeep

If grade of concrete is M20
Then after 7 days it will be 2/3 of 20 n/sq mm
Means 0. 666*20 = 13. 20 n/sq mm

Answer / devendra jatav

7 days - 70 to 75% strength
28 days - 100% strength

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