The raft foundation slab

THE HARDCORE BED

The purpose of the hardcore bed is to:

1) provide a 1) _____ bed that will keep the concrete slab warm and dry;

2) resist the growth of vegetation;

3) provide a level base for the oversite concrete.

The hardcore bed consists of material that resists 2) _____, such as broken brick, stone or rock.

The pieces should be large enough to ensure plenty of space so that 3) _____ isn’t trapped within the hardcore, the layers should be put down about 150-200 mm thick and flattened by hand with a tool called a 4) _____ to consolidate them. Also the machine called a plate vibrator can be used for large areas of hardcore.

The blinding

The finished hardcore has a rough, 5) _____ surface that should be smooth before laying the damp-proof membrane. It is done by laying about 50 mm of sand, ashes or weak, dry concrete slurry called blinding over the surface of the hardcore. The surface should be carefully leveled and there are no sharp 6) _____.

The damp-proof membrane

The membrane’s purpose is to prevent 7) _____ entering the building through the concrete slab. It is usually a heavy-duty polythene sheet that is tough enough to be handled on a building site without 8) _____ or puncturing. The material should stay intact even when workers walk over it while they fix 9) _____ in the floors and lay concrete. The dpm should be laid so that the edges 10) _____ the joints.

rammer, dampness, overlap, projections, moisture, open-textured, tearing, reinforcement, crushing, free-draining

10 Put the steps of making a simple raft foundation slab into the correct order:

Ground-floor slabs that are also raft foundation may have steel mesh reinforcement in the slab and the edge beams. The following steps show how to make a simple raft foundation slab.

1. Support the reinforcement 25 mm above the dpm by fixing cement spacers underneath the bars so that the concrete can flow all around them.

2. Build vertical formwork on struts along the outside position of the edge beams to contain the concrete.

3. Pour the concrete so that it fills all the spaces on the slab.

4. Spread hardcore and blinding in the measured area.

5. Divide the area into 3 metre by 3 metre bays (Figure 11.4)

6. Lay the reinforcement, the mesh for the slab and the bars in the edge beams in position.

7. Lay the dpm over the blinding.

8. Fix boards over the reinforcement to prevent the concrete leaking out.

Figure 11.4 Laying the Oversite Concrete into Bays

11 Fill in the gaps in the following passage with a suitable preposition given below:

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