TABLE OF CONTENTS Slabs on grade, also called floors on ground, are different from other structural members. First, they are supported directly by soil, and their success or failure may depend more on the soil qualities than on the slab construction. Second, floors on ground are among the few structural members that are open to the owner's eagle eye, and any crack or other perceived problem tends to be noticed and sometimes magnified beyond reason. And last, they carry equipment and floor finishes, and any defect in the slab's integrity or moisture resistance affects those elements. A floor slab undergoing drying shrinkage may not only crack, but also break the brittle ceramic tile it carries.
A typical floor on ground consists of a concrete slab of uniform or varying thickness with reinforcing, joints, and finish; a subbase of gravel or crushed stone; and a compacted subgrade. A vapor barrier, with or without a sand layer, may also be present in some circumstances. (The question of whether they are needed is debated in Sec. 6.7.) The reinforcement can be deformed steel bars, post-tensioning tendons, welded wire fabric, mixed-in fibers, or nothing at all. The typical components of a slab on grade are shown in Fig. 6.1.
Contractors often question the need for a subbase an added cost item for them. The function of a subbase is to provide drainage under the slab and to act as a cushion to help the slab span over weak...
