Applications

Construction: Stainless rebar for parking structures

Chloride corrosion leads to high repair costs for parking garages and underground car parks. How to optimize your investment with our Top12 steel.

In most countries an extensive use of de-icing agents in winter are not out of the ordinary. In Germany, up to 100,000 tons of de-icing salt are used daily in winter, which corresponds to approximately 0.5 tons of de-icing salt per kilometer in the event of a single ice rain event. With a tendency of increasing weather extremes, these numbers are likely to climb. The chlorides found in splash water and spray mist of these de-icing agents are the enemy of any steel reinforcement. Depending on their concentration, they lead to undesired corrosion on the reinforcing steel and as a result to costly repairs.

A single passenger car can drag along up to 7 liters of chloride-containing snow slush. Assuming the snow slush contains an average of 2M.-% chloride, this results in about 42 grams of chloride with every passenger car entering a car park. When cars are parked in underground garages, the slush thaws and the meltwater with a high chloride concentration can reach the neuralgic components. To protect the components from corrosion, either coatings or stainless reinforcing steel can be used.

Chloride exposure in paved parking garages

65% of paved parking garages have a chloride concentration of more than 0.5 wt%/z in the column base area

Investigations by Prof. Dauberschmidt on paved existing underground garages show that there is a high chloride load both on the rising components and on the foundations. Here are the most important findings on the neuralgic areas (hotspots):

Column feet (above top edge of pavement): chloride contamination exceeded 0.5 wt.%/z in 65% of the components examined, and even exceeded 1.0 wt.%/z in 42%.

Construction joint: In this area, chloride loads of more than 0.5 wt.% were found in 44% of all components examined.

Foundation top: Even in the deeper areas, chloride values greater than 0.5 M.-%/z were found in 28% of all components examined.

28% of paved parking garages have chloride concentrations greater than 0.5 wt%/z even with deeper foundations

Quelle: C. Dauberschmidt, F. Becker: Neue Forschungsergebnisse zum Schutz von Bauteilen unter Pflasterbelägen. Beton- und Stahlbetonbau 113 (2018), Heft 10, Seiten 737-745.

Top12 - Eliminate coatings from parking structures in a cost-neutral manner and reduce life cycle costs by up to 59% compared to standard coatings

The results for paved underground parking garages impressively demonstrate that in practice, corrosion phenomena are to be expected in unprotected supports, walls, foundations or intermediate ceilings of parking structures before the planned service life due to the high chloride exposure. To ensure the durability of parking structures, the designer must provide additional measures for the protection of reinforced concrete components exposed to chloride in accordance with DIN EN 1992-1-1/NA/A1. As a rule, OS systems or waterproofing are used as additional measures.

Cost-neutral replacement of coatings

According to the new DBV Code of Practice "Parking garages and underground parking lots", Top12, for example, can also be used as a stainless steel reinforcement as an alternative to a coating - and at the same manufacturing cost.

Wherever possible, Top12 is selectively used only in areas exposed to chloride. In areas without chloride exposure, B500B is used consistently. This means that Top12 and B500B are often used in mixed reinforcement in the same component, which reduces both the quantities and the costs of Top12 per component. Despite electrical contact between the two steel grades, contact corrosion can be ruled out.

Quelle: F. Becker: Dauerhaftigkeit von Stahlbetonbauteilen unter Pflasterbelägen. Vortrag auf 3. Münchner Bausymposium, 26.09.2018. (German only)

Lowest life cycle costs for parking structures

Source: A. Schießl-Pecka, A. Rausch (2019): Lebenszykluskosten für Parkbauten. Gutachterliche Stellungnahme 18-369/2. Ingenieurbüro Schießl Gehlen Sodeikat GmbH, 24.10.2019 (German only)

The use of Top12 as a stainless steel reinforcement saves considerable costs compared to a coating throughout operating life. If no coating system is available, all associated follow-up costs during operation are also eliminated, i.e. cleaning, maintenance and repair costs due to necessary coating renewals. Comparing different design variants merely on the basis of manufacturing costs is therefore only a very short-sighted focus. In order to consider and compare variants holistically, not only the manufacturing costs but also at least the follow-up costs in use or during operation must be taken into account.

Taking manufacturing and operating costs (= life cycle costs) into account, the use of Top12 is the most economical solution over a service life of 50 years.

Chloride loads in paved parking garages

65% of paved parking garages have a chloride concentration of more than 0.5 wt.%/z in the column foot area

Investigations by Prof. Dauberschmidt on paved existing underground garages show a high chloride load on both the rising components and the foundations. Here are the most important findings concerning the neuralgic hotspots:

Supporting pillars (above the upper edge of the pavement): The chloride load was above 0.5 wt.%/z in 65% of the components investigated, and even above 1.0 wt.%/z in 42%.
Construction joint: In this area, 44% of all examined construction elements were found to be exposed to chloride loads of over 0.5 wt.%.
Top of foundation: Even in the lower areas, chloride values greater than 0.5 wt.%/z were found in 28% of all components examined.

28% of paved parking garages have a chloride concentration of more than 0.5 wt.%/z, even with lower foundations

Source: C. Dauberschmidt, F. Becker: Neue Forschungsergebnisse zum Schutz von Bauteilen unter Pflasterbelägen. Beton- und Stahlbetonbau 113 (2018), Heft 10, Seiten 737-745.

Extreme chloride loads on ramps of underground car parks

In order to protect conventional reinforcing steel from high chloride loads caused by imported de-icing salts, ramps are often coated. The high mechanical loads caused by approaching and braking traffic, lead to high wear and tear on the ramps and thus high maintenance costs for the coating systems. This results in unplanned short maintenance cycles (usually 10-15 years), during which damaged coating systems have to be repaired or completely renewed at great expense.

By selective use of Top12 in the concrete surfaces, coating systems can be completely dispensed with, see variant A2 in the DBV information sheet "Parking garages and underground car parks". With low reinforcement contents, the Top12 variant is even cost-neutral compared to the usual coating. Any higher construction costs caused by Top12 are compensated for in the short term by the maintenance-free nature of the stainless reinforcing steel. Minimal life cycle costs are the result. Furthermore, access to all parking spaces remains guaranteed for the planned service life, as there are no blockages due to otherwise normal maintenance work.

Relevant downloads

Brochures

Top12 and Top700 Application brochure

German only

Technical datasheet

Top12 technical data sheet

Certificates

Top12 Technical approval coils

Top12 Technical approval bars

Certificate of conformity

Stainless reinforcing steel for the construction industry

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