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Pittsburgh Parking Garage Coating

The building in Pittsburgh was built in about 1920 and the parking garage needed to be renovated in order to refinance the building. Mild deterioration of some concrete required treatment with a more generalized protection coating applied for long term, low-maintenance of the garaging area which is exposed to residues left by automobiles during winter driving conditions.

Problem.

One of the most important causes of deterioration of concrete structures such as parking structures is corrosion of the reinforcing steel (rebar). Corrosion activity is caused by the elimination of the passive, naturally-occurring, oxide layer on the reinforcing steel. This is typically due to exposure to chlorides in the environment such as de-icing salts or saltwater along the coastline which is brought in by the vehicular traffic. It drips onto the floors and readily works its way into the tiny cracks and joints in the concrete structure where it encounters the rebar.

Rebar in new concrete undergoes a natural process whereby the steel exposed to concrete’s high alkalinity and forms a thin, passive film on its surface that resists corrosion. It’s the failure of that film that leads to corrosion and deterioration in not only car parks, but also bridges, buildings, platforms, tunnels and concrete pipes.

The protective layer is nano-scale layer and made up primarily of iron hydroxides and measures between one and 10 nanometres thick. The smallest human viruses measure 20 nanometres across.
The rate of corrosion is reduced to as little as one micrometre per year when reinforcing steel is protected by this passive layer.

However, corrosion accelerates when the film is attacked by chlorides from road salts, de-icers, or sea water. Concrete is weakened not only by the deterioration of the steel, but also by the growth of oxides on the steel surface. Rust can represent as much as six times the volume of the steel itself and can create enormous pressure that fractures the concrete surrounding it, leading to major cracking, delamination and spalling. Over time this can seriously affect the structure’s integrity.

Over 50 per cent of bridges in North America are made of reinforced or pre-stressed concrete, about 40 per cent of which have severe deterioration problems. Corrosion of steel is one of the main causes of this deterioration.

Solution.
The applicator coated the side walls with 30 mils of Ecodur (White) and treated spalled concrete on the first floor ceiling to prevent exposed rebar from rusting and stop further deterioration. A 40 mil membrane was also laid down on the second floor to prevent any additional future damage from occurring on the first floor.

The Ecodur forms a very long lasting, impermeable membrane that retains its flexibility while coping with extremes of temperature, acid and alkaline environments. Being non-toxic and biologically inert, it also zeros any risk from demolition or removal at some future time.

Application results
The coatings went on quickly and effectively and, with a cure time measured in seconds, and no noxious solvents involved, the structure was ready for use the next day.