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<< Facilities Management
By Simon Bustow, LEED® AP O+M, RPA
The reinforced concrete slabs which are used to construct an underground parking structures crack over time. Those cracks can be nearly invisible or as wide as 1/8” to 1/4” and they occur naturally as the concrete structures expand and contract with the changing seasons or under the stresses of changing and moving loads. During inclement weather, water and road salts are brought into the garage by the cars parking there and the salty mixture penetrates the concrete slabs through the cracks and attacks the reinforcing steel embedded in the slab. These salts are unavoidable unless you wash the bottom of each car as it enters the garage. The reinforcing steel corrodes and as it corrodes it expands. The expansion of the reinforcing steel then widens the cracks further and accelerates the penetration of more water and road salts. Eventually the combination of the expanding reinforcing steel and the widening surface cracks causes chunks or layers of the concrete to break away from the slab leaving pot holes that may become tripping hazards. Left unchecked, the corrosion of the reinforcing steel can structurally weaken the parking structure.
Several steps can be taken to slow the process as much as possible.
First, regularly wash down the garage trying to wash as much of the road salts down the drains as possible (this includes at least one annual complete power washing and monthly regular hose washing during the winter months).
Second, every year rout and grout the cracks that have developed since the year before. If possible complete rout and grout during the summer months to capitalize on lower occupancy and the fact that it is easier to identify the cracks when the concrete is expanded due to warm weather. Rout and grout can also be labeled grind and seal. The practice is such that wherever a new crack is found, its top surface is enlarged or opened up with grinders and an epoxy or latex grout is installed. This helps keep the crack from being another avenue for salty water to reach the steel.
Third, a penetrating corrosion inhibitor/sealer is applied every five to eight years or so to the concrete surface. This liquid acts as a sealer preventing some of the water penetration and it acts as a corrosion inhibitor that penetrates the concrete and inhibits or slows the corrosion of the steel.
Finally, in some garages, a flexible traffic bearing membrane is installed over the high traffic areas of the garage. This membrane is a flexible rubber coating that bridges over any cracks the slab the might develop and acts like a waterproof barrier.
As always, it is important to share this information with the parking garage population to help them better understand the minor inconveniences that main be experienced. The entire repair job length will vary depending on the size of the garage and extent of corrosion.