Site Visit 5 - Concrete Pour for Raft Slab (House)

The following photos show the preparation of and concrete pour for a raft slab (house). The site is for a two storey dwelling at the rear of a subdivided property in Parkdale, Melbourne.

Foundations and blinding can be seen in this photo. The blinding, which requires a weaker grade of concrete, has been poured at 600mm deep as the site is at a low point on a flood plain and therefore the slab needs to be raised above flood level. Apparently there is a lot more concrete needed for this job than their would normally be due to the location of the flood plain.





Plumbing lines which have been raised above the top of the floor slab and string guides can be also be seen. Pads which are built ip with soil between the strengthening beams have a 150mm thick layer of sand on top and have been prepared with guides for screeding.
The vapour barrier, bar chairs, and reinforcement have been laid. Square reinforcement has been laid on the top of the pads and rectangular between the pads (on top of the strengthening beams). The site has now been prepared and is ready for pouring (At this point it was 7:05am and we were waiting for the concrete trucks to arrive…)






Polystyrene blocks were put in place for the later application of brickwork and a rebate will be formed underneath the polystyrene blocks for the brickwork to sit on. The blocks have been tied back to rough but very sturdy formwork with pins as indicated in the photo.















There are some site specific issues on this job. A telegraph pole and lines are located very close to the property which can be seen in this photo, therefore a boom cannot be used and the concrete has to be pumped through a horizontal line.














The concrete pour is about to begin....

The external channel has been poured first and so far the concrete truck has been replaced just the once.

This photo shows the concrete being pushed into the rebate below the polystyrene blocks.

As a boom can’t be used the concrete hose line has to be moved manually. As concrete is incredibly heavy when wet, the hose needs to be dragged over pegs with a hook.

Unfortunately I was unable to stay for the whole process, and did not get to witness the screeding and the final finished slab, but I now understand how a slab is prepared and poured.