Concrete slabs are reinforced with steel bars. If the bars are exposed to moisture, they begin to rust. This process causes the steel to expand making the material around it brittle. The material around the bars starts to crack, which is a process called spalling. The condition will worsen over time until repair becomes necessary.
Many different things can trigger spalling, including harsh weather conditions and human error during installation. Causes may include stress fractures formed by general wear-and tear, especially in elements that bear a lot of weight. These fractures allow water to penetrate the surface and react with the steel. In heavy rains, if the reinforcing steel is too close to the surface of the slab, water can seep in and cause lime in the steel to oxidize.
Improper installation can cause a variety of problems, including premature spalling. Inadequate steel preparation can compromise the structural integrity of the slab. A poorly poured substrate is something else that can allow moisture to get to the steel through voids and cracks.
Spalling on the exterior of a building looks bad but even worse, it can cause a dangerous situation that could result in grave injuries. With continued exposure to the elements, the material will continue to deteriorate to the point that it will literally start falling apart. Pieces that fall off can cause property damage or personal injury if someone happens to be walking by when the pieces fall.
Signs of concrete cancer can be spotted with periodic visual inspections. Signs of damage include bubbling, also called plating, crazing and cracking of slabs.
Additional signs include any rust stain that appears to be leaking from the slab or leaks in overhead surfaces.
Repairing this problem requires the skill and experience of a professional since the bulk of the cost will be related to labor and access. In most cases, the repair will involve a tailored solution to deliver the most technically sound and cost-effective solution. This process usually involves removing all loose material, replacing the rusted rebar with new steel, and pouring new concrete.
Property owners who want to prevent this problem from occurring in the first place can have waterproofing membranes installed to decrease the likelihood of leaks. Property owners in marine environments should consider painting surfaces with products designed to resist chloride. This lowers the risk of corrosion caused by salt water.
It is never wise to ignore damaged slabs. Small problems will only become worse with time. Prompt attention to problem areas can save a property owner time and money while protecting against lawsuits that can be filed for personal injury or property damage caused by distressed concrete slabs.