Extending a concrete slab

[princhester]

I had a slab put in by our landscaper for a watertank . Naturally, since then I've realised I want a slightly bigger tank. I need to extend the slab by about 300mm or so.

The slab will have about 5.5 tonnes of water sitting on it, and not only that but we have clayey soils, which I know are hard work for slabs.

Is there any way of strongly joining the slab extension into the original slab? I suppose I could drill into the existing slab horizontally so that I can have reo that goes into the old slab and forms part of the new. Though the reo wouldn't be tightly held into the old slab.

Hmmm.

Any ideas?

[goat]

drill the holes for the reo on a angle( / \ / \ / \ <--imagine that 6 pieces of reo going in to the slab) this will tie the extension to the main slab and won't move as it won't have a direct pull on the reo m hope that makes sence

[Ian007]

Is there any way of strongly joining the slab extension into the original slab? I suppose I could drill into the existing slab horizontally so that I can have reo that goes into the old slab and forms part of the new. Though the reo wouldn't be tightly held into the old slab.

Hmmm.

Any ideas?

if you get the drill bit for these horizontal holes as close to the size of the reo their should be no slop or you could epoxy the rods in place if their is any slop in the fit.
Use larger reo than normal as the edge strip is only small, if you are buying the concrete get a higher slump than normal because of the same reason, or if your mixing the stuff yourself use more cement in the mix.
remember concrete is close to its max strength after 28 days but will still get stonger after that but at a much slower rate.

hope that helped
Cheers Ian

[Lucas]

When doing concrete on drives of servos we use 16 mm bar (round not reo) 12"-18" long to pin
these are about a foot apart and no expantion joint stuff is used
we also use a high MGP concrete (buy the concrete mixed dont do it yourself .... much stronger)
this is left dry for 5 days before driven on

[princhester]

Thanks very much for your answers guys. The only bit I didn't quite get was this:

Use larger reo than normal as the edge stip is only small...

What's edge stip? Why does this mean I should use larger reo than normal?

Thanks again.

[Arron]

Though the reo wouldn't be tightly held into the old slab.

From my limited experience, I dont think this is true. I've just had to do this with 10mm round reo into 10mm holes. The reo had to bashed in with force and is held in so tight nothing will get it out.

I was also told to use lots of bondcrete on the join, though I have no idea whether it really helps or not.

Arron

[Pulpo]

When I have had an expansion joint in concrete I use some sort of steel locking key, assuming the first slab has not been poured.

This locks the first slab to the second, I know its no good to you for the first slab has been poured but you could look at one of these to see if you could adapt, some how securing it to the first slab.

I have not used one of these steel locking expansion joints for sometime and cannot remember much detail about them, but its just an idea.

Even with the reo drilled into the first slab [epoxy the 16mm reo] I would want some sort of expansion joint between the old and new concrete, I have seen cracks otherwise.

As for the clay soil, you could put down some crusher dust first, also you could dig some holes for concrete piers in which the slab sits on.

I would be inclined to have ready mix concrete delivered.

Pulpo

[Ian007]

Thanks very much for your answers guys. The only bit I didn't quite get was this:


What's edge stip? Why does this mean I should use larger reo than normal?

Thanks again.

Whats an edge stip?
its a typo thats what :eek:

Cheers Ian

[princhester]

OK, thought it might be, but still why does the edge strip being small mean use large reo?