reusing barn shop slab as base layer

[Wave_Existence]

Lost my barn/shop in a fire, demo is done, and now I'm staring at the old slab. It's 35 years old, about 4–6" thick, with one frost heave crack. Budget's already tight from cleanup, so I'm wondering: can I break up the old slab, compact it, put down 4–6" of 2B stone, and then pour 6" of new concrete over that?

Never thought about doing "concrete over concrete" until now, but hauling off the old slab is money and labor I'd rather not burn if there's a workable alternative. Anyone here tried this approach? Did it hold up long-term, or does it end up moving/cracking worse than starting fresh?

 

[El VMX]

Sorry to hear about the fire. About the slab, a lot of people try to reuse old concrete to save money and labor. It can work as a base layer for your new slab but you have to be careful. The key is to break it up into smaller pieces, maybe three to five inches in size. And you need to make sure the base is compacted really well before you add the new stone and concrete. The biggest risk is that the old cracks will show up in your new slab if you don't prepare the base correctly. It's a gamble for sure, but some have had success. What are you planning on using the new barn and shop for?

 

[stev3njr]

Lost my barn/shop in a fire, demo is done, and now I'm staring at the old slab. It's 35 years old, about 4–6" thick, with one frost heave crack. Budget's already tight from cleanup, so I'm wondering: can I break up the old slab, compact it, put down 4–6" of 2B stone, and then pour 6" of new concrete over that?

Never thought about doing "concrete over concrete" until now, but hauling off the old slab is money and labor I'd rather not burn if there's a workable alternative. Anyone here tried this approach? Did it hold up long-term, or does it end up moving/cracking worse than starting fresh?

yeah, reusing the old concrete can work, but it's all about how well you process it. You can't just break it up into big chunks. you need to crush it down to something that resembles crushed aggregate or 2B stone itself.
you might need to rent a specific concrete crusher or an attachment for your excavator to get it to that 2 inch minus size.
If you don't crush it small enough and compact it incredibly well, those larger pieces will settle unevenly and you'll get reflective cracking right through your new 6 inch slab. If the old slab has rebar or mesh, you also have to deal with that mess, it can ruin your compaction effort