Mud Mat f'c

[RJ62]

Are there any guidelines for choosing a "lean" concrete design strength?

I have a project that calls for 125 ksf bearing pressure, on rock, and the use of 2000 psi "lean" concrete for backfill of undercut.

Why 2000 and not 1000, or 750psi concrete? Is it based on cost or is there a design methodology?

Jefferys

 

[SlideRuleEra]

All of the numbers you suggested should work well. One reason to make the "lean" concrete a little "richer" (say 2000 psi) is to decrease the waiting time until you can use it.

http://www.SlideRuleEra.net

 

[BigH]

Agree with SlideRuleEra - here in India they typically use 8MPa for under light structures and 12MPa for heavier - but this is overkill in my view. Remember that a "good" strength for soil is in the order of only 350kPa for bearing - so almost any strength of lean concrete is better that that - and a mud mat is only for protection, helping to set formwork/rebar, etc. Normally, in Canada I've used 1000psi - what is that? about 6 to 7MPa?

 

[dmoler]

If you want to be able to excavate for utilities, 100 to 150 psi is max. Dont forget the poor trench diggers.