Gen3 concrete - recipe?

[hj]

Hello. I've got a coupe of pads to pour for some steel posts. The pads are 1000x1000mm and about 800-900mm deep.

I've got loads of 25kg bags of cement, tons of builders sand, and a cement mixer. So, I thought I might DIY mix it myself. I can pick up aggregate as required.

Has anyone got a recipe for Gen3 mix (which was specificed by Structural Engineer)?

I've never mixed concrete before, so has anyone got any tips for me?

 

[theprinceofdarkness]

Try :- //www.diynot.com/diy/threads/casting-a-concrete-padstone-in-situ.58527/
Frank

 

[theprinceofdarkness]

Tips? I lay my bag of cement on its back and cut it in half using 1/2 bag cement and 14 slightly heaped large shovel fulls of all in ballast is meant to make 1:2:4 mix. Problem is that really is the max for a 90l mixer and you want more sand and gravel 18 shovel fulls? A better way would be to use a domestic sized bucket, I suspect a builders bucket may be too big. If you keep your sand dry, then you can just heap everything including the water into the mixer and let it mix knowing it will come out right. if the sand is wet,it will take longer and you will end up adding water to taste. Do gauge everything out, including the water ( about 50% of cement volume)
Frank

 

[hj]

Thanks Frank Much appreciated.

 

[^woody^]

builders sand

What is "builders sand"? You cant use building sand in concrete.

 

[hj]

Yeah thx Woody. Not soft/builders sand but sharp sand.

 

[tony1851]

Gen 3 will be something like 1:3:6 cement/fine agg/coarse agg.

 

[hj]

Thanks. So how long would it take to mix a cubic meter of concrete? Remember, I've never done this before so appreciate it's a novice question. Would there be any issue of concrete setting at the bottom of the pad before the top is mixed and poured?

 

[tony1851]

That's a lot of concrete - prob. over 2 tons; don't know how long to mix.

It doesn't matter in practice if it's done in layers and the lower layers go off first.

 

[noseall]

Just get two tonne bags of ballast and 14 x 25 kg bags of dust.
Chuck 3/4 of a bucket of water and six shovels of ballast into the drum and add half a bag of dust. Then chuck another six shovels in and add a bit more water.

It ain't rocket. Two tonne is a mornings work.

 

[tomfe]

Just to complicate things (and make me sound cleaver) the general purpose cement you get in 25kg bags has more fillters in it compared to mix companies about 50 compared to 33%. So a gen 3 mix would have to be altered to reflect this.

 

[hj]

Just to complicate things (and make me sound cleaver) the general purpose cement you get in 25kg bags has more fillters in it compared to mix companies about 50 compared to 33%. So a gen 3 mix would have to be altered to reflect this.

So I should add 20% more cement?

 

[tomfe]

Just looking again and thats quite a large pad, how many are you doing?
if it's more than one then it might be cheaper to get ready mix.

Re mixes, I am just being a dick, if you mix it yourself do as others do and 1:6 or 1:5 to be on the safe side but it's still not a gen3 mix:

This is a commercial mix not for gen3
Cement 52.5 - 400 kg/m3
10mm aggregate - 1000 kg/m3
Sharp sand - 800 kg/m3
Water (mains) - 200 litres/m3 (same as kg/m3)

The cement is graded at 53.2% CEM I general purpose cement is about 30% CEM II/L or LL, white cement is around 45%. Gen 3 has 4-20mm aggregate

 

[hj]

Just looking again and thats quite a large pad, how many are you doing?

3 in total. 2 of them are partly filled already with existing foundations, so I'll be using rebar rods to tie the existing and new concrete together. All spec'ed by the SE.

I've got a load of cement that I need using up, so self-mix is fine. Am plannng on doing them one at a time over a weekend.

 

[noseall]

Ive gotta laugh.

We are talking about large lumps of concrete here. Just crack on and chuck in a 6:1 mix with enough water to make it sloppy. Over-engineering and over-thinking getting in the way of common sense.