Suspended ground slab and collapsible cardboard voidformer and durability query - AS3600

[geopat69]

Hi There

A concrete suspended ground floor slab (commercial building) is being poured on 150mm cardboard void-formed. The slab has top and bottom reo.

So the slab (even though it is a ground slab) is going to be suspended 150mm above the ground once the concrete cures and the cardboard decays.

In terms of durability for the bottom reo and AS3600 cover requirements, is it still "poured against ground". Clearly it's NEAR the ground but not poured against it.

Thus, could you argue that it is A1 classification (assuming not agressive soil)

 

[Tomfh]

A1 is likely a bit of a stretch for an industrial building. What line of table 4.3 do you think applies?

I’d have thought A2 or B1 more likely...

 

[geopat69]

Hi there Tomfh
A2. It requires only 20mm cover for 40mpa.
I guess the issue is if the 150mm gap classifies as a suspended deck as opposed to being in contact with the ground. If it's treated purely as suspended (exterior above ground and temperate) then it's 20mm. If it's treated as in contact with the ground, then it's 20mm plus 10mm (for against ground with polythene)

 

[hokie66]

Why would you want to use less than 30mm cover?

 

[geopat69]

Because this is an acedemic question based on a code interpretation rather than using it in practice

 

[geopat69]

.

 

[Tomfh]

I don’t think it’s a particularly nice environment under there, and would err on the side of more cover, particularly since you can never see it or repair it when it rusts.

Are you suggesting A1 or A2?

 

[blihpandgeorge]

I would see this as A2 exposure (says a commercial building - so non-residential in standard). I dont consider this as against ground as the cardboard will decay and leave some space there so the underside will not be against any water. Notwithstanding, i dont see any benefits in skimping on cover.