Slab-on-ground construction is the simplest type of slab, yet the most durable, it provides an excellent "earth coupling", enabling the floor slab to achieve the same temperature as the earth a few metres below the ground surface where temperatures are more stable ie cooler in summer and warmer in winter.
A typical stiffened raft slabs consist of:
- 100 mm thick concrete slab
- edge beams
- internal beams (except Class A and Class S sites)
- steel reinforcement.
Waffle Raft Slabs
Reactive soil sites can be difficult to build on, but 'floating' stiffened concrete raft slabs cope well with these conditions. Waffle raft slabs use void formers at regular intervals, forming closely spaced deep reinforced beams criss-crossing the slab underside. These void formers are mostly expanded foam boxes
Features of waffle raft slabs
- they are used on flat sites
- they are wholly above ground
- no beam excavation is required
- no controlled or rolled fill is used
- slab panel/void formers are used
- slab panels are on 1 metre grids (approximately)
- trench mesh or individual bars can be used
- slab thickness is 85 mm
- internal beams are 110 mm wide
- there is minimal concrete volume
- no beam down drag from clay (above ground slab) occurs
- shrinkage of slab is lower than stiffened rafts and footing slabs
- they use 30% less concrete than a stiffened raft
- they use 20% less steel than a stiffened raft.