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I am about to install galvanized steel posts in fast setting concrete (QUickrete Fence n Post).
Someone suggested that in order to save money I could break up smaller pieces the old concrete bases (I will have to do that anyway so I can move them to the car to dispose them) and put some of these smaller pieces of concrete in the holes and pour fast setting cement in.

Would there be any problems with this move?

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    If you choose to proceed don’t forget that the new mix is thick and doesn’t “pour around” the old chunks very well. I’ve actually done this for fence posts without problem but you need to alternate adding chunks and new mix to the hole. If filling with chunks first THEN add new mix to the top there will be many air pockets. I wouldn’t do this for say a wall or anything structural, holding fences posts tho I have done it. – Tyson May 19 '18 at 17:07
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It would be appropriate to substitute your old concrete for the gravel at the bottom of the hole (assuming you broke it small enough...), but I wouldn't mess with the concrete mix itself.

Think about it: you'd be upending the factory mix by adding more 'gravel'. Manufacturers have thought about the mix more than we can imagine, so I'd defer to them.

While I get that hauling more bags of concrete and more waste is a pain (maybe dribble the waste concrete out in 5# increments in your household waste, if permitted), you might take comfort in amortizing your work over the life of the posts.

  • I am thinking about big concrete chunks, I am not going to crush it to gravel size I am thinking about pouring concrete, then add this remains and then add more concrete. The pieces of old concrete that I would add will be positioned in such a way to allow the new concrete dust to get in the spaces between the old pieces and they I pour water. The result will be that the old concrete will be set in the new one when the new one solidifies – MiniMe May 19 '18 at 19:15

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