Can I pour a concrete foundation in multiple pieces?

Question

I'm building a 25-meter (65 foot) block retaining wall. The engineering specifications require a concrete foundation for the block wall equal to about 4 cubic metres (141 cubic feet) of concrete, with reinforcing bar/mesh throughout. This includes 10% waste.

Due to access problems on our (rural) property, the premix concrete supplier will need to make multiple deliveries with a small truck. However, they won’t guarantee the deliveries will all arrive within a particular time window, or even on the same day. I don’t want to get halfway through pouring a single foundation only to find out the next delivery won’t be for another day.

My proposed solution is to pour the foundation in multiple sections to guarantee each section will be completed in a single pour. Reinforcing bar runs between sections joining them together, and formwork used to hold each section in place until the next section is ready to pour.

Question

Can I pour the foundation in a number of smaller segments which are joined by the reinforcing bar but poured on different days, or will this result in a severe structural problem for the wall sitting on the foundation?

Is a better approach to hire my own mixer and pour many small sections, similar to what is described in this question?

Answer 1

I agree with Ecnerwal, yes you can do that. I also agree to extend the rebar past the pour (drill holes in the form boards and extend the rebar out the holes).

Code (and the CRSI) requires 30 bar diameters. So, if you’re using #4 bar (1/2” diameter), then you need to extend it a minimum of 15”.

Answer 2

Yes, you can do that. Provide plenty of rebar length past the joint. The vast majority of commercial projects are poured in sections, and virtually everything more than 60-70 years old was poured in sections.

Answer 3

Yes. To get better results please do the following:

1. have rebars continuously, or leave an adequate splice length, across the joint.

2. at the end of the leading pour, prepare the joint with a little slant and roughen the surface, then cover the leading pour with plastic sheets.

3. on the day of the second pour, clean the joint with a water wash and wait till the solid concrete appears to be moist but surface dry (no hanging water). You can fasten the drying time by spreading/applying a thin layer of cement on the joint that would absorb the water and help bond the concrete of different ages.

4. wet curing the concrete at least 7 days after the last pour.

Side View of the Concrete Footing:

Note: If you choose splice over continuing the rebars, please check with your engineer or the local code regarding the splice length requirement.

Answer 4

As others have said, the first thing to do is to carry the reinforcement beyond each “day” joint to give continuity of reinforcement.

As long as adjacent concrete sections are poured within approximately 3 days of each other, the individual sections of concrete will fuse as the concrete cures and the cement hydrates to create a single contiguous piece of concrete.

Answer 5

Yes, you can.

In addition to the rebar extensions you may consider applying concrete bonding adhesive depending on the time between pours.

Answer 6

We had a similar issue with retaining walls and multiple pours.

Based on that and what we learned, this would be my approach to your problem:

First, the biggest issue by far, is steel close to the surface or crossing a join. Your problem then becomes,how to be certain that water can't flow (however slowly,even through a join), and over time cause corrosion and degradation.

There are systems for that, but they tend to be specialised and often, expensive.

I'd ditch the entire problem by avoiding it, totally

Your supporting concrete (4 cu.m over 25m length) is equivalent to 0.16 cu.m. per linear metre, or for example,a footing 40 x 40 cm (or 25 x 60 cm etc) along the whole 25m length. The structure supported, is a retaining wall.

A wall that length, the footing is providing ground support. It almost certainly doesn't matter if its actually cast as 3 x 8.3 m sections, because the ground load spreading will be identical. The middle part isn't relying on the end parts for support, because it's too long and thin - if it needs support, it will have buttressing designed in, by the engineer,it won't rely on full length steel for it.

So I would check with the engineer, is it okay to cast the footing as say, 2 ~ 4 lengths of 6 ~ 12 m each. In each section, stop the steel 70mm before the end, and restart it 70mm into the next section.

I would expect this to give identical results with no risk, and no need to take protective measures for the joints. It will still look and act exactly as the original design would have done. (It sounds like).

At the absolute worst, you gain control joints every 6~ 12 m, which is a good idea anyway. It means that if the ground was going to have poor support in an area (could be likely over a 25m run?), the original would quite possibly have uncontrolled cracking, exposing steel. Very bad idea. This way, each section is shorter and much more likely to act as a whole, under stress. Any cracking will manifest at a section end, where steel won't be exposed. If that kind of settlement happens - it would have happened anyway, most likely and this way is likely to control it better and make it much easier to make good.

But check with your engineer to be sure.