The O’Hare Airport parking garage has capacity of 12,000 cars and generates over $75,000,000 in annual revenue. The six level structure features cast-in-place, lightweight concrete slabs with mesh reinforcement and post-tensioned beams and joists. The garage operates 24 hours per day and renovation work was needed to accommodate continued operation. In addition to its normal parking function, the garage had been used for temporary offices.

Over the years, the concrete parking decks had deteriorated significantly. The penetration of water and deicing salts through cracks, joints and trench drains had caused extensive corrosion of the wire mesh, reinforcing bars, post tension cables and buried electrical conduit within the slabs.

Previous preventative maintenance efforts, which included annual linseed oil treatment, isolated deck and drainage repairs, and some cathodic protection on the exit ramp had not stopped the continued cracking, spalling, delamination and general deterioration of this parking structure.

A major renovation program ($90 million over 4 years) was initiated in 1995 by the owner which included complete structural restoration and waterproofing of the six parking levels, as well as replacement of all trench drains, electrical conduit and fixtures, plumbing improvements, new approach bridges, exit ramp overlays, attendant booths, ticket machines, painting and signage. Design engineering services including plans and specifications were prepared by McDonough Associates. Inspection engineering was provided by Gilbane.

The parking repair contract, awarded National Restoration, Inc., consisted of approximately one million square feet on levels 3 and 4, plus additional areas on levels 5 and 6. Work was scheduled in separate phases to minimize lost parking spaces and revenue. The partial depth slab repairs utilized polymer concrete and epoxy mortar (TPMŌ 77 FM) while the full depth repair concrete was 5000 psi Ready Mix with DCI additive and superplasticizer. All replacement reinforcing steel was epoxy coated. Concrete repair patches were tied into the existing slab using General Polymers EPO-FLEX Ō over the “cold” joints to accommodate minor movement differential.

Considerations for selecting EPO-FLEX Traffic Deck System as the traffic bearing system included the following:

• A system that would take continuous traffic, especially in turn radii.
• A system that could be installed relatively quickly and effectively bridge a significant number of stress cracks around the elevator centers.
• A system that would not have a high odor interfering with the operation of the other parking areas.

One of the critical benefits of EPO-FLEX technology over the traditional urethane systems is the ability of the epoxy to bond strongly to the substrate, as well as, the aggregate. This feature allows for simple repairs when needed, unlike urethanes, which tend to disbond in sheets once the system has been breached.

The installed system is comprised of EPO-FLEX, an internally flexibilized epoxy membrane, followed by an epoxy based wearcourse and tie coat. All of these materials are 100% solids and zero VOC. The system includes:

• A 25 mil EPO-FLEX basecoat membrane,
• 3550P Stress Relieving Epoxy wearcoat of 15 mils in parking stalls and 25 mils in drive lanes and turn radii, broadcast with nonskid aggregate, and
• A final topcoat of 3550P Stress Relieving Epoxy to lock the aggregate and provide ease of cleaning

The installation was accomplished on time and on budget. National Restoration Inc. was awarded additional contracts for subsequent phases due to the success of both the system and the efficiency of the installation.