"I am just running a few numbers, and could use some expertise from anyone who has ever poured large volumes of concrete.

I have a price for 50kg cement bags. I am looking to work out cost per cuft. So if I use a standard recipe of 1 part cement, 2.5 sand, 2.5 gravel, 0.5 water, I have 325kg of concrete. So how many cuft do I have?

Second, is there a stronger recipe to use? Something that can hold up to more punishment? Something that lasts longer in/near salt water?"

"Financially building the fortress of deathitude?
P.s. Using Rebar?"

"while drilling holes in a bank vault (don't ask!) "

"There are lots of things that make concrete harder but if you push that to it's extreme you can pour it like glass. There is gear called advancer, likewise you can get retarders. They are mostly used for quick setting or long pours, a twenty meter shaft can't be filled instantly so you add retarder, see? The advancer has the side effect of making the mix harder. Generally speaking the more dust (actual cement powder) you add the 'harder' your muck but that's not necessarily stronger. Unless it's a padstone for a column for instance.

(God, I'm crap at explaining things)

I was told the Romans invented 'Marine' saltwater setting concrete by adding volcanic pumice, and the secret was lost until the wily Japanese re-invented a process in the 1970s. There are a shedload of plasticizers and things to make the concrete waterproof but they are expensive! Otherwise no one would bother doing tanking, they'd just use waterproof concrete wouldn't they?

I've been on Ministry of Defence jobs that use full on waterproof concrete and it stinks. it smells of resin, like the mix the use for swimming pools and boatbuilding. So that's the hardness of the concrete and the water resistance. Neither of those is the strength which normally comes from the steel."

"Meters mate, concrete comes in cubic meters. Even in Britain, anything smaller than a cubic meter isn't worth counting, except in Polish labourer hours.

There are lots of things that make concrete harder but if you push that to it's extreme you can pour it like glass. There is gear called advancer, likewise you can get retarders. They are mostly used for quick setting or long pours, a twenty meter shaft can't be filled instantly so you add retarder, see? The advancer has the side effect of making the mix harder. Generally speaking the more dust (actual cement powder) you add the 'harder' your muck but that's not necessarily stronger. Unless it's a padstone for a column for instance.

(God, I'm crap at explaining things)

I was told the Romans invented 'Marine' saltwater setting concrete by adding volcanic pumice, and the secret was lost until the wily Japanese re-invented a process in the 1970s. There are a shedload of plasticizers and things to make the concrete waterproof but they are expensive! Otherwise no one would bother doing tanking, they'd just use waterproof concrete wouldn't they?

I've been on Ministry of Defence jobs that use full on waterproof concrete and it stinks. it smells of resin, like the mix the use for swimming pools and boatbuilding. So that's the hardness of the concrete and the water resistance. Neither of those is the strength which normally comes from the steel but while drilling holes in a bank vault (don't ask!) you will find metal disks mixed with the concrete as well as the rebar, that's to deflect the force of explosions so there's different kinds of strength as well. . .

Big old topic ain't it?
_"

" Last UK job I did was high security prison cells (don't ask) "

"For what you're wanting to improve in the "cement", harder isn't exactly better. I think you would want a bit more resistance, and disbursement of force."

"Wait, I'm confused. Are you asking about what sort of concrete to use for the house or for the retaining walls for each of the field steps?"