All buildings require regular maintenance, but parking garages are in particular need of regular attention because they are subject to harsher conditions than most structures. Parking garages are exposed to vehicular traffic and abuse, seismic stresses, moisture and temperature changes from the weather.

Parking garages in northern climates and along coastal areas also are exposed to salts, which can penetrate into concrete and corrode embedded metal reinforcing.

For these reasons, maintenance and engineering managers should develop sound inspection and maintenance programs to protect and prolong the life of parking structures.

Corrosion - The Enemy. Common problems: Much of the structural deterioration and failure in typical parking garage faces is due to corrosion of reinforcing and embedded metals. This corrosion results from long-term exposure of the concrete to moisture and chlorides from deicing salts or airborne salt spray. When water and chlorides penetrate into the concrete in sufficient concentrations, embedded steel or other metal begins to corrode.

Since corrosion by-products are much larger than the original volume of the steel, they cause expansive forces which results in internal cracking of the concrete. This condition then causes delamination, or loosening of the surface concrete from the concrete below (spalling), Eventually the concrete cracks and loosens to the point where surface concrete falls off or creates surface potholes and exposed rebar.

Cracks: Another significant problem with parking structures is cracking of the concrete. Cracks allow a direct path for moisture and chlorides to enter the concrete floor slabs, resulting in the premature initiation of the corrosion of the embedded reinforcing. Cracking in parking structures can be related to applied loads, seismic conditions, thermal expansion, long-term concrete shrinkage and restraint of structural movement.

Because parking structures are longer than typical structures, structural movement due to thermal changes or long-term shrinkage of the concrete can result in significant internal forces in the structure if such movement is restrained. If forces are large enough, cracking results.

Structural Maintenance: This includes repairing and patching areas of delaminated or spalled concrete on floors and ceilings, corrosion protection, sealing joints and cracks in floors, and maintaining protective waterproof coatings on floors.

Structural Repair Tasks

Concrete and rebar repairs: Repairs are required when surface concrete begins to delaminate from the concrete below, resulting in loose or spalled surface concrete. Typically, repairs should extended at least 3 inches beyond the area of delaminated concrete and should be chipped out to the least ¾ inch below any exposed reinforcing.

Concrete patch edges should be sawcut without damaging embedded reinforcing bars. Exposed concrete and steel surfaces in repair openings then should be sandblasted clean. Then all exposed reinforcing bars and tensioning posts should be painted with a protective coating. Once the coating has cured, the repair opening can be recast using concrete patching material. Modern concrete patch materials cure very quickly to enable traffic.

Crack and joint sealing: Left unsealed, cracks and joints become easy paths for moisture and chlorides to penetrate into garage floor slabs and expansion joints. So it is important to seal these openings and to keep seals intact over the structure's life. Maintenance personnel should check sealed cracks and joints at least annually and repair to assure the crack sealants and joint seals are still effective.

Protective Coatings: Once repairs are made, it is important to apply vehicular grade waterproofing systems to protect the structure and minimize future deterioration. Even garages in good condition benefit from the installation of a vehicular grade waterproofing systems which limit the amount of moisture and chlorides entering the concrete. Building owners and maintenance managers see that vehicular grade waterproofing membrane systems are applied long before concrete deterioration beings, which greatly prolongs the amount of time under repairs are required.

Waterproofing strategies: The choice of a waterproofing system depends somewhat on the condition of the garage and the exposure of the floor. For example, a fairly new garage with minimal chlorides in the concrete can benefit greatly from the application of a penetrating sealer. But this sealer might not be adequate protection for an older garage already experiencing corrosion-related delamination and spalling of the concrete. In a garage having a significant amount of cracking in floor slabs, a traffic-bearing waterproof membrane system probably is appropriate because of its cracking-bridging capability. All top level floors should have waterproof vehicular traffic membranes applied.

When considering long-term cost, waterproof membrane systems typically are better. Properly maintained membranes can provide 15-20 years of service life.

Follow-up Inspections: inspection could be limited to a full visual inspection and localized sounding of the concrete for delamination. A more involved evaluation also might include inspection openings, concrete sampling and testing, and structural analysis. A way to make routine inspection more cost-effective is to use in-house personnel to perform intermediate inspections to look for deterioration and distress. This tactic could delay the frequency of the engineering inspections. But managers still should schedule engineering inspections to be performed every three-to-five years. Inspection to determine whether structural repairs are required by experienced engineer should be as often as every two-three years, depending on the condition and exposure of the structure.

Parking garages are unique structures that require regular inspection, maintenance and repair, Managers can minimize deterioration by scheduling regular maintenance, including structural maintenance repairs, perhaps every three to five years, depending on the structure's condition. If a structure is protected by an effective waterproofing coating, the time between structural repairs increases.