M40 is the strongest as it means that it will reach a targeted concrete strength of 40 N/mm2 at 28 days. M20 means that it will be designed to reach a strength of 20 N/mm2 at 28 days.
Generally, increased strengths are achieved by adding more cement, although other additives can help.
A M20 concrete cannot be theoretically be stronger than M40 as it is being designed initially for a lower strength gain; - if it achieves a higher strength than 20 N/mm2 at 28 days, then it is not really an M20 mix.
Hopefully this has clarified matters
M-40,M-20 At any grade of concrete depending on as per the
client requirements, but any grade of concrete curing time
7 to 28 days means the compreesive strength should be
(20n/mm2) 7 days (40n/mm2)28 days
We don't need mixing
proportions. we are
making our concrete into
a ball shaped, and to raise
upto 1m height and fall
down. if that's does'nt
break then that's the best
mixing and also having