Can MOT be used for concrete?

ThisIsWeird

Apart from not having actual sand in it, its make-up looks pretty similar - chippings to dust.

Silly Q?!

MikeJXE

It depends what the intended use is 

ThisIsWeird

MikeJXE said:

It depends what the intended use is 

Thanks.

I guess not for structural stuff - founds and that. Possibly paths?

Section62

ThisIsWeird said:

Apart from not having actual sand in it, its make-up looks pretty similar - chippings to dust.

The difference is in the distribution of particle size - the grading curve.

MOT sub-bases have a grading curve which makes them ideal for compaction, there's a defined range of particle sizes from dust through to approx 60mm.  The %age amount passing through each grading sieve is the key part of the specification, and there should be some in each.

Sand/ballast used for concrete is usually gap-graded.  You aim to have a %age of fines (sand) and then a %age of coarse aggregate, usually in the 10mm to 20mm range. The quantity of stone in the 2mm - 10mm range is usually* minimised for general construction work, the "gap". (*but when designing a mix for special purposes this can be varied)

There's no specific reason why you couldn't use MOT for making concrete, but you'd need to increase the cement content to suit the grading and to achieve adequate strength.  For workability you'd probably also want to remove most of the stone >20mm as otherwise it will be difficult to lay.

Given the cement is the most expensive ingredient in most cases it is cheaper using a standard sand/ballast mix (optimised for cement economy), rather than using a possibly cheaper but not ideal aggregate supply.

P.s. Concrete above ground (like paths) generally needs to be made and laid more carefully than below ground concrete (like foundations) due to weathering (esp. frost) and ground movement due to changes in water content.  A path is usually 'structural' in the sense it transmits loads from the surface into the ground below, and has to resist ground movement.

stuart45

It really clogs up the mixer.

ThisIsWeird

Two absolutely brilliant answers, gents - each in their own way!

Love it And thanks.

FreeBear

A bulk bag (800Kg) of either MOT1 or an all in one ballast is £70 from the likes of B&Q, so no savings to be had on the price front. Use the right aggregate for the job, and you won't have to worry about doing it again in 10-15 years time.

ThisIsWeird

Thanks FreeBear.

The real reason I asked is that I have a half-bulk bag left over, and stuck it on Fb along with a quarter bag of Aggie and ditto of sand. The latter two went quickly, but no-one wants the MOT. :-(

The guy who collected the Aggregate began by mistakenly shovelling the MOT into his smaller bags for taking away...

Section62

ThisIsWeird said:

The guy who collected the Aggregate began by mistakenly shovelling the MOT into his smaller bags for taking away...

You didn't let him finish the job off?

ThisIsWeird

I wish I had now...

stuart45

Are you selling it, or giving it away?