Foundation extension for terrace with "used" sand?

Dear forum,

I am new here and hope for some good advice from you so that I can successfully carry out my current project. It is about renovating an old terrace. I have several questions about it, but I will post them in separate threads so that the answers will hopefully be helpful to others as well.

Currently, paving slabs lie on sand on a concrete foundation. I want to extend the concrete foundation by 65 cm. Now the question arises whether I could use the sand for the concrete. Normally, you would either use ready-mix concrete or mix cement with concrete gravel (1:4), but I thought that I would otherwise have to dispose of the sand and could kill two birds with one stone. That would save effort and costs. As far as I understand, cement with sand is less load-bearing, but I think in this case it might not necessarily be significant. On the other hand, I do not want to do a poor job. The sand is not mixed with soil because it lies on the foundation slab.

What is your recommendation on this topic?

Best regards, Pivi

Recommendation: Give away sand via classifieds so that children can enjoy it and then do it properly :)

The smaller the grain size, the less stable the concrete is. With sand, you will more likely get mortar with correspondingly lower load-bearing capacity. A professional probably wouldn’t do that; as an amateur, of course, you can botch it as much as you want. For a few garden chairs, it will probably be enough, but 2 trailers of gravel aren’t that expensive.

The smaller the grain size, the less stable the concrete is. With sand, you tend to get mortar with correspondingly lower load-bearing capacity. A professional wouldn’t do that, but as an amateur you can of course botch it however you like. For a few garden chairs it will probably be enough, but 2 trailers of gravel are not that expensive.

It’s more about the effort than the cost, but I see both previous answers go in the same direction, so get rid of it. Thanks in advance!

I am new here and hope for a few good tips from you so that I can successfully implement my current project. It is about renewing an old terrace. I have several questions about this, but I will post them in separate threads so that the answers will hopefully be helpful to others as well.

Sorry, I had to help a friend finish his birthday cake last week, otherwise I would have definitely answered you right away: if your project discussion is to be helpful for others (and not least for you), then do NOT scatter it across fragmented threads where it drives you crazy to keep the facts clear! It is best to close the metastasis threads, not without referring to this one with a link.

So, I also do not consider your scattering with your threads to be meaningful!
Regarding the question: I miss the word "Kies"! Is it really sand like, for example, the Baltic Sea beach or is it rather coarse gravel?