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Structural Repair PARKING PROBLEMS
A compulsory inspection and maintenance regime is essential to maintain the safety of the UK’s ageing multi -storey car parks, says the Concrete Repair Association
Other issues in these ageing structures can be associated with the form of construction. For example, where precast items are used, movement of the structure may reduce the adequate bearing surfaces. This could potentially lead to failure over time and the need for remedial measures, such as the application of purpose-made metal brackets, designed to pick up the required load, should a failure occur during service.
Car park in need of repair
Poor maintenance and inspection has led to many of the UK’s concrete multi-storey car parks, falling into disrepair. Built in the 1960’s and 1970’s, many are showing significant signs of deterioration and some could even be in danger of structural failure.
To improve the situation, the Concrete Repair Association is supporting a call from the British Parking Association for the introduction of a compulsory inspection regime for these structures.
Car park structures are expected to undertake similar duties and withstand similar exposures to bridge structures, and yet they are designed to a less rigorous design code and, unlike bridges, are not subject to a fully-documented inspection regime, laid down in legislation.
While there are owners/operators who take their responsibility seriously and spend considerable amounts of money taking care of their car park assets, there does not appear to be any formal regime in the form of a voluntary code of inspection. And, although guidance is available from the Institution of Civil Engineers (ICE) document, Recommendations for the Inspection, Maintenance and Management of Car Park Structures, it is unclear how many owner/operators have taken on board its recommendations or are even aware of it.
The result is that these structures can develop structural faults which can remain un-noticed.
The problem
Deterioration in concrete car parks is caused, in the main, by chloride based de-icing salts being used in the car park or brought into the structure on vehicle tyres. These chloride salts allow corrosion of the embedded reinforcing steel and, ultimately, significant spalling of the concrete.
Corrosion of reinforcing steel results in the loss of steel cross- section, which may significantly restrict load-bearing capability and may lead to punching shear issues in the area of the columns.
The corrosion problem can sometimes be exacerbated by owners who apply a car decking system to eliminate water from the concrete in an attempt to overcome such issues and limit further corrosion. Where corrosion rates and chloride levels are well advanced, corrosion may continue beneath such coatings, remaining hidden until the point of spalling, or even worse.
New column head
Work to column heads may involve using pre-bagged fluid flow materials to increase column head dimensions. This requires a very exact regime to ensure that the load from the slab is correctly ‘picked up’, through the precise location of new reinforcement and attention to detail in the production of the necessary formwork.
Use of a proprietary fluid-flow concrete, containing various additives including expansive agents, will ensure that the load
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Concrete repair techniques To address punching shear issues and widespread corrosion of the reinforcing steel, work must be conducted to increase the size of columns heads; or remove the concrete to expose the corroded steel and enable its
replacement. Concrete removal may be carried out using the latest concrete cutting techniques, such as very-high-pressure hydro-demolition, or conventionally using hand held breakers.
Breaking out of concrete will continue chasing along the steel reinforcing until a point is located where the cross-sectional area is structurally acceptable. In the case of a waffle slab, this may simply leave a lattice of the ribs, with whole areas of the slab having been removed. In order to replace this concrete homogeneously, it is necessary to have waffle moulds to replicate the original dimensions. New versions will have to be created, if the original construction moulds are no longer available.
is ‘connected’ with the material being introduced into the watertight formwork. Holes accurately cored down through the deck from above allow both the introduction of the material and the venting of any air from the shutter as the concrete is injected.
Once work is completed, the application of a waterproof/ wearing surface to all car park deck surfaces will offer long term protection to the structural integrity of the deck slab and protect the embedded reinforcing steel from the aggressive chloride ion solution. Reference should be made to the European Liquid Waterproofing Association, Specification and use of Liquid Applied Car Park Deck Systems.
Hydro demolition in repair area
Column head reinforcing Spalling under existing coating
To ensure the continued structural integrity of the UK’s car park structures, a more rigid regime of inspection and maintenance is essential. Furthermore, it must be ensured that all inspections and repair works are conducted by competent personnel who have a full understanding of the deterioration mechanisms associated with car park structures and how these may be adequately arrested to ensure a continued service life.
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