Casting concrete directly to pile cap which has muddy water

[LewisLiew]

Is that appropriate if casting concrete directly to pile cap which has muddy water at bottom of pile cap & hole for water flow through at side formwork? I was told concrete can push water due to its density. Will it absorb some water and weaken it's strength? Would like to know reasons if not appropriate.

 

[Just Some Nerd]

Whenever I go inspect some footings, even if the site is bone dry in the middle of the desert I'll still note to make sure the base is fully drained and cleaned out prior to pouring concrete. Muddy bars are also a pet peeve of mine.

 

[phamENG]

No, it's not okay. They need to de-water that excavation.

There are ways of pouring concrete underwater, but they require specialized skills and equipment. If the contractor is saying 'the concrete will displace the water' as their only justification to just dump concrete into a mud pit, I seriously doubt they possess those skills.

If this were a solid block of concrete, then yes - it would displace the water. But wet concrete? If you let it free fall into the excavation you'll get mixing at the bottom, causing elevated w:c ratios (weaker concrete) or you may end up washing the aggregate (loose rocks, no concrete at all) at the base of your cap. Neither are a good solution between heavy loads above and a pile below.

 

[dik]

It's not good practice but unless the muddy water is adhering to the rebar and cap, it will not likely cause any problems. Think of it as tremmie concrete in a muddy river.

 

[phamENG]

Think of it as tremmie concrete in a muddy river.

That only works if they are actually using the tremmie method. If they are just dropping this in from several feet above the bottom, the bottom of their pile cap will have, at best, questionable quality, strength, and durability.