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Structural strengthening of corrosion-damaged reinforced concrete slabs

To restore the load-bearing capacity of a parking garage slab severely damaged by steel corrosion, solidian GRID was applied as an approved supplementary reinforcement solution in combination with cathodic corrosion protection – without shutting down the parking levels below.

Project description

At the Dammstraße parking garage in Ludwigshafen, significant corrosion damage was identified in the upper layer of reinforcement. Severe chloride-induced reinforcement corrosion made structural strengthening of the slab necessary.

A complete replacement of the upper reinforcement layer would have required the closure of the parking levels below and caused significant operational downtime. Therefore, a strengthening solution had to be found that required the removal of as little chloride-contaminated concrete cover as possible.

The strengthening solution had to be implemented while allowing the structure to remain in use.

Technical challenge

• Chloride-contaminated concrete in near-surface areas
• Severe corrosion of the upper steel reinforcement layer
• The lower reinforcement layer was intact and needed to remain so permanently
• Ongoing building operation had to be restricted as little as possible
• A complete replacement of the upper reinforcement layer would have taken several levels out of service
• The structural strengthening had to be verifiable and suitable for inspection

Solution

For the first time, approved solidian GRID carbon reinforcement was used as supplementary reinforcement for strengthening an existing load-bearing structure. Based on the general building authority approval of solidian GRID carbon grids, the reinforcement could be designed and statically assessed in accordance with the DAfStb guideline for concrete components with non-metallic reinforcement.

After removing the chloride-contaminated concrete cover, a 4 cm thick concrete overlay made of C30/37, reinforced with up to two layers of solidian GRID Q95-C-EP-s38, was applied. In addition, a cathodic corrosion protection system (CCP) with titanium mixed oxide mesh anodes was installed to permanently secure the remaining load-bearing capacity of the existing steel reinforcement.

The compatibility of the carbon reinforcement with the cathodic corrosion protection system was verified – no impairment of the CCP system by the carbon layer occurred.