Post-tensioned parking structures can last 60 years or more when designed for durability. Durability design systems control entry of deicing salts and protect reinforcing steel even when chloride ions penetrate the concrete. To achieve these goals, redundant durability systems are needed, that is, if one system fails, a backup system must come into play. The recommended approach incorporates several durability elements:
- The first and most basic durability system is the concrete used in the slab. Low permeability requires a low water-cement ratio.
- The desired drainage slope for floors is 2 percent, but never less than 1.5 percent.
- Surface sealers slow water and chloride entry into the concrete. They are not waterproofers, however, and don't bridge cracks.
- Control joints and construction joints must be sealed with a high-quality traffic-grade polyurethane sealer to prevent deicing salt entry and subsequent deterioration of rebar.
- Increasing concrete cover over the reinforcing steel increases the distance the chlorides must travel in the concrete to cause corrosion.
- Epoxy coated rebar increases the durability of bridge decks by withstanding the deteriorating effects of deicing salts.
- Covering the post-tensioning tendon from anchorage to anchorage prevents contact with the concrete or with migrating water and deicing salts.