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HI friends,
For footings and pedestals my architect told to use M20. We used the ratio of 3:7:9 (3 cement, 7 robo sand and 9 (20 mm jelly (architech/engineer concurred with the above). After three days back filling of earth is going on. Contractor has put the 10 mm rods for pedestal beyond the plinth and he started cutting the additional length of pedestal rods (10 mm) from the second day after layin the pedestals. I find that the pedestal is still soft. We are regularly putting water and we covered with gunny bags and pouring water frequently. Today we filled earth and filled the pits with water also. How long it will take for curing and becoming strong?

with curing, it should get 99% of M20 after 28 days. IIRC 90% by 14 days and two-thirds by 7 days.

curing for footings and pedestals or anything under the ground is very easy - keep pouring water into the pit or the back-filled pit.

From our experience, 3:7:9 on paper is fine. It is very difficult to control the gang of workers who pour cement, sand and jelly into the mixer. To make things worse, they use different size thattas.

We could control the gang only by keeping a book and counting. When we didn't count cement was used less, even though it was a labor contract with material supplied by us. I guess gangs working for material contractors are accustomed to a combination of 1 for cement, 3 for sand and 5 for jelly; approximately. When we counted it was good. 7 day test gave us a strength that of M25; M20 is good enough.

thank you very much sateeshpnv.

Hi,

curing the concrete improves to attain the strength desired for the concrete grade made for.

for pedestals the reinforcement required is 8dia rods(0.12%).

Regards
Manjunath.K.N,
Structura Designer

How can we test the grade of concrete achieved after 7 days and 28 days test? Is there any equipment to test it?

Thanks,
Ramki

In our case, Ultratech person collected a sample of concrete mix, tested it in their lab and sent us results in email. That's when we knew it was M25 while we needed only M20. Ultratech engineer repeated it for another slab and the result was similar.

Independent testers include civil aid. I'm not aware of others. BTW, we got civil aid report, before placing the order, from our solid cement blocks supplier, Dicon.

If you want to test the quality of an existing one, I guess it will damage a piece of the structure.