Spalled describes concrete whose surface has cracked and broken away in fragments. In parking structures, spalling is most often caused by corrosion of reinforcing steel, although freeze-thaw damage, impact and poor construction can also cause it.
Deicing salts carried in on vehicles soak into the deck. When chlorides reach the reinforcing, the steel corrodes, and rust occupies several times the volume of the steel it replaces. The expansion cracks the concrete, a hollow layer forms (delamination), and eventually pieces break away. Spalls on soffits and beams can fall onto people and cars below. See chloride-ion contamination.
Finding and fixing it
- Condition surveys. Visual inspection plus sounding with a hammer or chain drag to find delaminations before they fall.
- Immediate safety. Remove loose concrete overhead and protect areas below.
- Repair. Remove deteriorated concrete to sound material, clean or replace corroded steel, and patch with suitable repair mortar or concrete.
- Protection. Sealers, traffic membranes and corrosion protection to slow the next round. See expansion joints for related leak paths.
The Parkonomics view
Spalling is the visible end of a process that started years earlier. Regular condition surveys and timely sealing cost a fraction of the structural repairs that follow neglect, and they keep concrete from falling on customers.
Related terms: Chloride-Ion Contamination, Expansion Joint, Post-Tensioned Concrete, Concrete, Life Cycle Cost