Inspection of post-tensioned parking structures shows that expansion joints in parking floors are subject to a number of problems including inadequate sealing, spalled slab bearings and insufficient concrete cover over tendon anchors. If the sealant does not accommodate the movement of the slab due to creep, shrinkage and temperature changes, then water may intrude into the joint and freeze. Debris may also accumulate in the joint. When rising temperature causes expansion of the slab, the pressure of the ice or debris against the free slab end can cause cracking.
Also, inadequately sealed expansion joints leak chloride-laden water onto adjacent slabs, beams and columns. The water causes deterioration due to corrosion of reinforcement and freeze-thaw damage to water-saturated concrete. Mineral deposits and spalling on surfaces below joints are early signs of potential distress. Unless bearing surfaces are protected, for example with steel angles, there may be distress at slab bearing points. Spalling may develop due to excessive forces exerted at edges and corners. And fluorocarbon or other polymer slip bearings, used to facilitate slab movement, must be installed with care or they will tend to work out of position and tear.
At slab ends, at least 2 inches of concrete cover over anchors for post-tensioning tendons is needed for protection against corrosion-causing drainage. Generous cover is particularly important in case spalling develops at bearing points. Such spalling has been found actually to expose anchors in one structure where cover was skimpy. Designers must make careful estimates of slab movement over the seasons due to creep, shrinkage and thermal effects. It is usually desirable to isolate stairways at the ends of parking structures, and to rely on the concrete frame for resistance against lateral loads.