Slabs-On-Ground - Structural Deterioration And Damage

Problem: Cracking of slab - 2.

Cause: Curling of the slab.

As new concrete dries, it shrinks or shortens in all dimensions. In the case of concrete slabs-on-ground, the top surface of the slab is prone to shrink and dry more rapidly than the bottom surface. The tensile strength created in the top of the slab and loads on the unsupported corners can cause the concrete to crack. While in most cases the effect is unnoticeable, in extreme circumstances, bumps, spalling and cracking can result as shown in Figure 39a and 39b.

Figure 39a - Curled Concrete Slab

Figure 39b - Cracked Concrete Slab

Solutions: Minimize shrinkage of the concrete.

• Thicker slabs will tend to curl less than thinner slabs.
• Provide control joints in areas such as penetrations, where cracking is likely to occur.

Problem: Cracking of slab - 3.

Cause: Inadequate structural strength of slab.

Cracking will result where the structural strength of the slab cannot support the applied loads. The Portland Concrete Associations recommends control joints be located at intervals of 16 to 23 feet (5 to 7 m) in both directions.

Solutions: Ensure that the slab is adequately designed.

• When slabs-on-ground are intended as a structural element of a building they need to be designed by an architect or structural engineer skilled in the work concerned.
• Concrete used in slab-on-ground construction should have a minimum strength of 4,350-psi (30 MPa).