concrete pad 7m x 7m

[Zebsport]

Hi,
Next week i'll be laying a 7m x 7m concrete pad 6" thick for the base of a wooden garage/workshop i'll be buiding.
The area was excavated last Oct, 8" of type1 laid and wacked every so often along with being weathered in.
I'm thinking of laying them as 2 seperate pads as 7x7 seems to large on its own. The concrete guy said its best to pay £5 extra per metre and have fibres added to the mix, anyone had experience with this? Also that rebar is a waste of money? A friends lending me some steel shuttering, which should save time. What gap between the 2 slabs should i leave?

Any advice much appreciated,
Zeb.

 

[PaulJR]

Fibre reinforcing will go some way to stop cracking, but reinforcing steel is NOT a waste of money.

If you want to do it in 2 pours, then set your shutters (roadforms by any chance?) at 7m x3.5m and pour one half. Following morning strip the shutters and refix to pour the remaining slab against yesterday's concrete. if you want to create an expansion joint put some flexible filler board (Flexcel, Korkpak etc.) in the joint and seal the top up with a 12mm deep run of sealant , but its not really that necessary on such a small slab. You might consider setting dowel bars in the joint - to stop differential settlement

If you want to prevent the slabs cracking then fix some steel mesh (A252 if you can get it - Ø8 bars at 200mm centres) so that it is 50mm below the top surface. Don't drop it in after you have concreted - it will sink all the way to the bottom and be useless. You can buy mesh at builder merchants, about £10 per 2.0x1.0m sheet ISTR

 

[Shytalkz]

Should put some dowel bars between the two pours too. Doesn't need an expansion joint.

 

[Zebsport]

Thanks for info. Yes thay are roadforms, seems like a really good idea. Much easier than trying to stake in wooden shuttering.
Do you think its worthwhile to connect the two pads. You mention dowels, is this simpley pieces of rebar fixed into one pad and sticking out into the area to be next poured?

 

[PaulJR]

yes that is exactly what dowels are - usually Ø12mm bars about 600mm long - it will stop one pad lifting relative toi the other - you might get a small step in the slab over time, which would p!ss you off a bit.

Road foirms have holes in them already for just this job

 

[Shytalkz]

As Paul says, Zeb

 

[noseall]

The concrete guy said its best to pay £5 extra per metre and have fibres added to the mix, anyone had experience with this? Also that rebar is a waste of money?

I would be more inclined to say the fibres are a waste of money. A regular C20 mix alone will be ok for a well compacted shed base.

7m x 7m is large but two blokes could manage it. You could have a temporary mid-span shutter or tamping board that could be lifted out and filled before trowel finishing.

Are you having it pumped or shot straight in from the wagon?