I’m getting started on my cabin project. I was hoping to get some concrete recommendations for the piers. The piers will be built using plywood forms. Temps are cool up here rignt now, in the 50’s, proably won’t freeze at night. The piers will be above grade and astectics are important. The piers will be subject to Wisconsin free-thaw. Because of high, uneven bed rock, we need to pour some rock pockets (over excavation) at the same time as the piers. If the mix is too thin, the concrete will try to extrude out the bottom of the forms. I’m thinking I need a higher slump. It’s only 4 yards of concrete, but the truck will unload 800 feet away into a mud buggy. This means the buggy has to travel 1/4 mile per load. The buggy will then dump it’s load into a trough from where it can be shoveled into the forms. We’re amatures, so despite the cool temperatures, I’m concerned about the concrete kicking on us. This is why I included a retarder.
Here’s the mix that I came up with, please feel free to modify…
7 bag mix (4,000psi)
6-8% air entrained
3-4″ slump
Fiber mesh
Retarder
I presume we’ll need to rent a vibrator? The bug holes wil be pretty bad even if we work the concrete as it’s poured?
Replies
Your mix is fine.
Your mix should be fine.
I would be very leery of a concrete vibrator in inexperienced hands - It is incredibly easy to over vibrate and separate the aggregate.
A safer way would be to vibrate the outside of the forms - by rapping with a hammer or mallet or even holding a bladeless reciprocating saw against the form.
As far as the concern of concrete leaking underneath the forms - either shovel in a stiffer slump for the first few inches or you can seal the bottom of the forms with spray foam.
Terry