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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?

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    Contact two suppliers. Or are you so far in the backwoods there is only one choice.
    – Solar Mike
    Nov 28 '21 at 17:30
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    Consider a pumper truck. It would need to make it part of the way back, then the mix trucks would only need to make it to the pumper. It would cost more, of course, for the extra rental, but should ensure you get it done in one day. The pumper may be able to bring extra hose to make it all the way from the road to the pour site.
    – FreeMan
    Nov 28 '21 at 17:36
  • @SolarMike There's three suppliers in the area: one only does big commercial jobs, one doesn't have any small trucks, so I really only have one option.
    – guest12345
    Nov 29 '21 at 2:28
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    Whatever you do, especially because you're in a rural area, when the concrete truck does arrive, make sure they're carrying a delivery ticket and check the batch time on it. This is exactly the sort of job where they'll try to stretch the time between the batch and delivery by throwing water in the mix to keep the concrete workable for longer, but adding water ultimately weakens the concrete and can lead to a poor job. 90 minutes is the standard for batch to discharge time so be wary if the delivery ticket shows a batch time that's much older than that.
    – J...
    Nov 30 '21 at 14:30
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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 CSI) require 30 bar diameters. So, if you’re using #4 bar (1/2” diameter), then you need to extend it a minimum of 15”.

Edit: CSI = CRSI

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    Out of curiosity, it seems the OP is using the metric units as the primary, and I guess you are from Canada, which uses metric units as well, why provide the information based on the imperial units? What is the code then? What is CSI - Construction Specification Institute, or short for CRSI, or...?
    – r13
    Nov 28 '21 at 20:20
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    @r13 Us Canadians are weird, we mix and match metric and imperial.
    – crip659
    Nov 28 '21 at 20:46
  • @crip659 Yes, the US is the same, but my instinct is to provide the units I practice the most when facing a question with dual units listed.
    – r13
    Nov 28 '21 at 20:55
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    @crip659 us Brits are pretty weird when it comes to units too. We're still mostly Imperial, except when we're not. Nov 30 '21 at 16:18
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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.

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  • FYI- this was flagged as "low quality". While concise, some additional "meat" might not hurt.
    – FreeMan
    Nov 28 '21 at 18:20
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    @FreeMan so 50 words or 500 words if BS just to pad it out?
    – Solar Mike
    Nov 28 '21 at 20:32
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    The algorithm likes long answers. Having failed in a quick search for some handy reference from the ACI to point to I'm not overly concerned about it. The vast majority of commercial projects are poured in sections, and virtually everything more than 60-70 years old was poured in sections. It's valid.
    – Ecnerwal
    Nov 28 '21 at 22:29
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    You've actually got my upvote (now, I meant to do it earlier). I was just pointing out a fact - this ended up in the low quality review queue. I voted that it was OK.
    – FreeMan
    Nov 29 '21 at 0:28
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    Single sentences trigger that warning. I try to post two, like this.
    – Criggie
    Nov 29 '21 at 22:08
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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.

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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:

enter image description here

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

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    Your #1 does not make sense. Does that mean install rebar at 2” on center or 3’ on center?
    – Lee Sam
    Nov 28 '21 at 18:39
  • #3 is not necessary. You are not trying to bond the two pours together with “a thin layer of cement “ as you call it. Bonding between the two pours comes from the rebar lap… a layer of cement does not bond a footing together. This is a retaining wall. Lapping of the rebar so loads are transferred through the joint is what is important. Identical compaction under each sector the footing will do more than a film of cement on the footing. (Slabs are bonded together with cement.)
    – Lee Sam
    Nov 28 '21 at 18:50
  • #2 - which way should the wall slant? Should it slant toward the cement being poured today (so the length at the bottom of today's fresh concrete is greater than the length at the top) or should it slant away from the cement being poured today? Also, what benefit does that bring? I'm not challenging you, just looking for clarification.
    – FreeMan
    Nov 28 '21 at 18:52
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    "prepare the joint with a little slant", not "wall", sorry that was a typo in my question. I still don't know which way the slant should go, and I'm curious what that buys one when joining sections of concrete. I honestly don't know, so I was asking. Also, I'm sure that by now you know how to identify moderators 'round here, so you should be able to figure out that I'm not one. Sorry if you chose to take offense at my question, I was simply looking for clarification.
    – FreeMan
    Nov 29 '21 at 0:32
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    @FreeMan the image is a side view, not a top view. The slant is "like a mountain" - the bottom sticks out more than the top
    – Caius Jard
    Nov 30 '21 at 20:23
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Yes, you can.

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

enter image description here

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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.

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