matty01

Will ordinary portland cement with a small amount of sharp sand make a strong concrete ?
Would it be stonger with no sand at all,just plain cement?
Is there a significantly stronger cement on sale generaly?
Cheers

Jap2Scrap

A 100% cement mix will be hard as f*&k and will probably crack as soon as the cold weather sets in.

What's it for? I ask because a 4/1 mix Sand/Cement is suitable for most outdoor applications and internal flooring.

Kyl3cook

If you want a concrete, you'll have to put and aggregate in the mixture, otherwise it's just cement...what's it for?

john_s

iTrader: (1)

If you want a reasonable concrete mix, use 4 parts stone to 2 parts sand to 1 part cement. If you want anything more technical than that or of a guaranteed strength, you will really have to order it from one of the readymix companies.

What are you doing with the concrete? How strong do you need it?

John.

ed_the_duck

If u want it for a drive there is a mix called slab concrete and its rated to 30 newtons.
Bout 300 quid a load.........saves a lot of graft

fast bloke

Concrete gets most of its strength from its thickness (and proper prepatation.) The type of cement used wont make much difference as long as you use decent ratios. As above, premix will be more precise and probably more thoroughly mixed. If you need something super strong get precast slabs. (The things they use for multistory carparks - v v expensive though)

Dunk

iTrader: (1)

Vibrate it if you want a good 'un. (If it's small use a flat bed sander )

D

David Lock

Concrete has super compression strength but very little tensile strength. So for a driveway you might need to think about some mesh to prevent it cracking as soon as something heavy goes over it and slab sinks into subsurface a bit. If you have some hardcore or similar as a base and just light traffic e.g. cars then a 4" - 6" concrete slab (as john s above) will probably be fine. DL

NeilT

best mix for strength is a 1:2:4 mix, tamped or virbrated

Neil

Scoob99

iTrader: (1)

Whilst your their go find that **** Ecclestone and bury him under it

gsm1

As above, use a stone, sand and cement mix. There are also hardening and frostproofing additives you can use as well.

speedking

Also don't add too much water, the water/cement ratio has a great effect on strength. Of course with less water the concrete is much less workable and sets very quickly. As in all things its a balance. 100N/mm² concrete is achievable.

Are you making some boots

Silver Scooby Sport

iTrader: (15)

LMFAO

loony toon

iTrader: (4)

Add fibre mesh into the mix , unless you ever intend on moving it !!! its like fibre glass matting but when it cures with the curing cement it goes as hard as steel. Its used on suspended ceilings etc where strength is important but not thickness, i used it on a driveway and its had a 28 tonne lorry parking on it !!!!!!!!

Kyl3cook

oh, and remeber to cure it (hose it down for a few days to keep it wet)...as it will help prevent shrinkage cracks. The concrete strength is based on 28 days of curing, so in theory you shoudl cure it for this amount of time, however the majority of the strength is gained in the first 7 days (it's an exponential curve)....so once it's gone hard...keep it well watered.

matty01

Thanks guys,long day so no reply earlier.I'm bolting some heavy tall machinery to a concrete floor but the concrete isn't up to the job so i'm chopping out a section and replacing it with some (hopefully) stronger concrete.

NeilT

also, concrete continues to gain in strength up to 28 days, so the longer you leave it the stronger it will become.

(weeks of material science lectures come flooding back like a bad nightmare! )

Neil

edited to say oops - didnt read the last few posts stating the above already

john_s

iTrader: (1)

For a machine base, I'd bit the bullet and order some from a readymix company. There should be companies locally that will do smallish quantities (minimum might be 0.5m3. C35 mix at 50 slump *should* be OK... without getting into exact weights, loadings, etc (need a structural engineer for that). The floor will really need some mesh in, and dowel bars to tie it into the existing floor & stop it moving relative to it. Tamp or vibrate the concrete well to make sure there's no air voids.

As stated above, the concrete will gain about 2/3 of its quoted strength in the first 7 days, and will reach or exceed the 35N/mm2 in 28 days, and just keep getting stronger after that.

John.

speedking

How do you know? How do you know how big a section to cut out and replace. Good advice to tie in to existing but if the existing is really bad then this will not help much.
Hope it's a ground floor slab

David Lock

Just a thought - may be you could use a steel plate over existing concrete. Need to level it first but this would spread the load on existing floor which may be fine?? This would save hacking out and drilling to tie in existing floor with bars. DL