Question: I understand the effects chlorides have on reinforcing steel in concrete. What effects, if any, do chlorides have on plain, nonreinforced concrete, which is typically used in sidewalks and driveways?

Answer: Properly designed concrete mixes and careful attention to placing and finishing should produce a plain concrete slab that is resistant to chlorides. In some exposed concrete slabs, the chlorides in deicing chemicals have attacked the surface of the concrete and led to surface scaling. In most cases, this situation has been caused by low air content, overfinishing, or finishing with rainwater or bleedwater on the surface. A plain concrete slab with adequate entrained air and a low water-cement ratio at the surface should resist scaling from deicing chemicals. Eliminating birdbaths and low spots in the surface of the slab during placement also contributes to good performance. Allowing concrete to cure thoroughly also can improve resistance to scaling. After the concrete has dried for at least 28 days, apply a sealer to help keep out salt and moisture during service.