REPAIRING UHPC ELEMENTS

Is it possible to repair UHPC elements?

REPAIRING ULTRA HIGH PERFORMANCE CONCRETE ELEMENTS

When considering using Ultra High Performance Concrete (UHPC) elements for a project, a recurring concern from contractors is whether it is possible to repair UHPC elements that become damaged or dirty during installation or the subsequent construction process.

This is a legitimate concern because a) it is not realistic to assume that all elements will get through the construction phase without any being damaged, and b) repair mortars and techniques normally used for conventional concrete elements are insufficient to ensure adequate quality of the repairs.

Repairs can be divided into two types: minor (superficial or aesthetic) repairs and major (structural) repairs. In general, minor superficial repairs can be performed by the contractor, while structural repairs require a specialist to ensure that the element's structural performance and durability are preserved (or restored).

HERE ARE SOME INDICATIONS TO CONSIDER

If the repair is less than 1-2 mm deep and covers an area smaller than an A4 sheet of paper, it does not significantly compromise the cover layer and does not require a specialist for structural reasons.
Corners and edges are difficult to repair, especially on stairs with high wear or on railings that are touched with hands. However, in most other places, it is safe to perform minor repairs yourself.
If the cause of the damage is fire, major impact, explosion, or similar, the risk of hidden damage is likely and should be assessed by a specialist before repairs. But "normal" impacts (dropping small equipment or props, elements brushing against each other or other building parts during installation) are usually not a concern.
The function of the damaged part can sometimes be critical. An example could be a corner used to connect two elements using dowels – any damage to that area could compromise the connection and thus overall safety. Another example is damage close to critical inserts or on the inserts themselves.

And of course, when in doubt, ask us for advice – a few pictures via email or mobile phone are typically enough for a quick assessment of whether it is possible to repair it yourself or not.

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PERFORMING MINOR REPAIRS

Minor repairs should be performed with a repair material that is as close to the original mix as possible – the best option is to get a small amount from the supplier, including instructions on how to mix and apply it. For CRC i2®, Hi-Con provides a special pre-mix that is identical to the material used to perform finishing work at our production sites.

This dry mix is combined with water to a consistency similar to chewing gum or clay and applied after thoroughly cleaning the damaged area. Just before application, the surface is moistened with a sponge or a brush. After pressing the repair material firmly into the repair cavity, it is left there for 15-30 minutes until it begins to set, and the surface can then be shaped/smoothed with a damp, firm sponge.

Previous experience with repair or finishing work is, of course, an advantage.

PERFORMING MAJOR REPAIRS

Structural repair work should only be carried out by a specialist with experience in UHPC repairs, following an initial assessment by the responsible project engineer.

For CRC i2®, it is possible to cut, drill, bond, cast, and even replace parts of elements with proper assessment, calculation, planning, and preparation, due to the material’s toughness. It is naturally difficult to perform major repairs without any visual effects, but with skill and experience, much can be achieved.

SUMMARY

All repair work that is possible in conventional concrete is also possible in UHPC – and more – but it requires specialized knowledge and skills.

As a contractor, the primary goal should always be to avoid contamination or damage to elements, but should an accident occur, this should not limit the use of UHPC.