What was the mix for this? Concrete

[Tigercubrider]

I want to cast a shape in concrete. It needs to be tough, but smooth on the outside.
An example of what I think would be suitable is in the pictures. There is a small amount of rebar in it but it looks to me to be mainly sand and cement? I was going to add the chopped fibre to the mix as well.

for scale, the concrete looks to be approx 4” thick.
Mine would be more rugby ball shaped and a bit bigger than a rugby ball.

TIA.

 

[scbk]

Is it something structural? Or just decorative?

 

[Tigercubrider]

It’s (hopefully) a Buck for a fuel tank.
I have made a plaster mould of the outside shape that I want (ie a negative) to fill with a concrete mix.
I started with a fibreglass cover intended to fit over a now no longer available fuel tank.

The idea is to come up with a solid concrete positive that I can use to shape aluminium on.
I would mainly shape the metal on a tree stump or similar but it would be good to be able to hit it sometimes
I would mostly use it to compare shapes but need solidity if possible.

 

[Mike13]

You need a 3:1 mix, and dont forget to give it a month to harden, sharp sand, not builders sand, and use a febmix or similar so you dont need too much water.

 

[Tigercubrider]

Thanks

yes, loads of time to cure.
I won't be bashing it too much but may be pushing down on it to bed reluctant (annealed) aluminium.