UKC

Quick question for the builders and engineers of the forum...

I know concrete doesn't really like getting hot and the surface can break up, but is there anything you can do to stop it? My wife wants a fire pit in the garden and as the surround will be concrete it makes sense to cast the bowl at the same time. Is there anything I can mix in to improve the thermal stability; I'd avoid any aggregate in the top layer as I know some rocks can shatter impressively when heated. I want to avoid going down the route of using refractory cement as it isn't normally very weather proof and works out pretty pricey! 

Thanks!

Make it oversize and line it with clay or firebricks perhaps.

Clay is a good idea, also cheap

If I had a load of fire bricks lying about I could find a few more interesting things to make:

https://hackaday.com/2016/12/05/insanely-hot-oven-makes-pizza-in-45-seconds...

Be careful 

youtube.com/watch?v=OeUqjYwhEik&

Fire clay is one option but even better you can use a castable cement for furnaces. Build the oven from refractory bricks. Make sure you take the time to bed it in, the cracking is the change of temperature and particularly the contraction from loss of water during first use.

Your firepit won't get near my 1600C furnace I'm planning to build my wood fired oven from same material.

Is the surround made from concrete because there is already concrete on the ground around where the fire pit will be?

When you use the cement in stoves and furnaces mentioned above, it is often mixed with iron filings and swarf (spelling). It makes the cement expand and contract at the same rate as the stove and doesn't crack etc..