Slab Design
Floor Construction Methods
A ground-supported floor slab is made up of layers of materials and components. The construction method has a bearing on a number of aspects of the performance of the floor.
Large area construction - jointed
Large floors up to several thousand square meters in area can be laid in a continuous operation. Fixed forms are used only at the edges of the construction at intervals of typically 50m. Concrete is discharged into the floor area and spread either manually or by machine. After the floor has been laid and finished, it is sub-divided into panels by sawn restrained-movement joints to relieve shrinkage-induced stresses, typically on a 6m grid in both directions. Typically, these free-movement joints open by 4-5mm.
Large area construction - jointless
Jointless floors are built using large area construction methods. No joints are sawn, but steel fibres incorporated into the concrete mix control the width and distribution of cracks caused by shrinkage. However, the formed free-movement joints at the edges of each area will be wider than in floors with multiple sawn joints and will typically open by 20mm.
Long strip construction
The floor is laid in a series of strips typically 4 to 6m wide, with forms along each side. Strips can be laid alternately, with infill strips placed later. They can also be laid consecutively or between 'leave-in-place' screed rails. With the latter method, large areas can be poured in a method similar to large area construction. Strips are laid in a continuous operation and joints are sawn transversely across each strip about 6m apart to accommodate longitudinal shrinkage. Formed free-movement joints are provided at intervals similar to those in large area jointed construction.
Pile-supported Floors
If geotechnical investigation indicate that ground conditions are inadequate for a ground-supported floor, the floor may be constructed on piles. In principle, any of the construction methods discussed earlier can be used, but most such floors are built with a jointless method.
(extract from Concrete Society Technical Report No.34 Third Edition)