Cast-in-Place Concrete Structure Repair
Cast-in-place (CIP) is one of the most common construction methods for concrete structures. Most problems with CIP structures are related to rebar corrosion caused by improper cover, cracking construction joints, and permeable concrete. Corrosion of this reinforcing steel leads to “spalling” of the surrounding concrete.
Slab deterioration is caused by corrosion of reinforcing steel and the resulting expansion of the oxide. On top surfaces of slabs, in areas of negative moments, flexural cracks create a quick and direct path for water, oxygen, and salts to reach the reinforcing steel. Where negative steel moment or top mat steel is too close to the surface, permeable concrete allows these deterioration mechanisms to oxidize the steel. The bottoms of slabs often exhibit similar issues as the top surfaces.
The bottoms of beams are most often affected by the intrusion of salts and by water that flows through expansion or construction joints. Heavily reinforced with large diameter reinforcing steel, successful repairs should fully expose the rebar and adjacent stirrups. After coating the reinforcing steel, forms are constructed to pump in concrete under pressure and leaking joints are repaired to prevent future deterioration.
The connection of slabs and columns often exhibit punching shear which can be an extremely dangerous structural condition. Failure occurs when the connection between the slab and column can no longer withstand the shear stress. This lack of capacity can be related to design flaws, construction error, or overloading of a structure.