Concrete floors and roof slabs are common in industrial buildings and parking garage structures.
When not properly maintained, premature deterioration can occur, leading to pieces of concrete on the underside of a slab breaking away from the rest of the slab. This creates a falling object safety hazard and puts the slab at risk for collapse.
Primary Cause of Deterioration
Water infiltration is the primary cause of most concrete slab deterioration. Air voids and cracks in concrete allow moisture to penetrate the concrete and potentially reach the reinforcing steel bars or wires in the concrete, causing them to corrode. As the reinforcing steel corrodes, it expands and exerts a pressure against the surrounding concrete causing the concrete to spall—meaning that pieces of concrete near the slab surface break away from the rest of the slab. Corroded reinforcing steel and spalled concrete reduces the load-carrying capacity of the slab.
Water infiltration can result from a leaking floor or roof finish covering a concrete slab. Parking garage slabs are especially susceptible to deterioration, often lacking a finish to provide an initial line of defense against water infiltration. Road salt mixed into water and snow dripping from parked vehicles during winter months can also accelerate deterioration.
What To Look For
Concrete slab deterioration may be difficult to spot when the slabs are concealed, such as those above suspended ceiling systems. Look for water spots and rust stains on ceiling tiles and other finishes that conceal slabs as a sign that further investigation, such as removing the tiles to expose the slab to view, may be warranted.
Slabs exposed to view from the underside often exhibit signs of deterioration. Efflorescence (white salt deposits on concrete surfaces), rust stains, and spalled pieces of concrete are tell-tale signs that your slab is deteriorating. In addition to repairing a deteriorated slab, it is important to fix any source problems that may have caused the damage, such as leaking floor and roof finishes.
Proactive Protection/Mitigation
There are steps you can take to be proactive and protect concrete floors and roof slabs from premature deterioration, including:
- They can be coated with a hydrophobic sealer or an impermeable membrane, when possible, to keep water from infiltrating the slab. It’s important to maintain the sealer or membrane, especially when directly exposed to the elements and wear.
- Epoxy-coated and other corrosion-resistant reinforcing steel can aid in reducing harmful effects.
- Advanced technologies, such as galvanic corrosion mitigation systems, are available to help keep slabs from deteriorating.
As a structural engineer, I am able to visually survey your concrete floor and roof slabs for signs of deterioration, conduct a sensitivity analysis of deteriorated slabs to determine if repairs are warranted and offer necessary solutions.
