Concrete Foundation Walls - Structural Deterioration And Damage

Problem: Deterioration from salt attack.

Cause: Weak, permeable concrete.

After several years of exposure to de-icing salts, some concrete will visibly deteriorate. Spalling and cracking are likely to occur as the salts permeate the concrete.

Solutions: Provide higher-strength concrete which is resistant to salt damage. A comparison of municipal sidewalks with garage and driveway slabs will often show a significant difference in durability - the sidewalk concrete lasts longer and looks better. The better performance results from higher-strength concrete and better placement procedures.

• Use concrete with a higher-strength design mix 4,350-psi (30-MPa), concrete with higher levels of air entrainment - 5% to 8%, or sulphate-resistant concrete. Ensure proper curing of the slab.
• Do not over trowel the slab. Over troweling, especially with a steel trowel, removes the entrained air and increases the water-cement ratio at the surface of the slab. Use a wood float and broomed finish to enhance durability.
• Seal control joints and saw-cuts in garage slabs with a flexible sealant to prevent the penetration into the slab of salts and moisture that is prone to freeze-thaw cycles as shown in Figure 20.

Figure 20 - Minimizing Salt Damage To Concrete Slabs

• Allow at least 30 days of air drying before exposing the driveway and garage slabs to freeze-thaw cycles.