Low Cover, High Risk

What is it, why does it, and how to fix?

“Concrete cover, in reinforced concrete, is the least distance between the surface of embedded reinforcement and the outer surface of the concrete.” You can check out Wikipedia if you’re not sure.

If there’s not enough distance – that’s called ‘low cover’.

Despite the general improvement in quality control measures, inadequate cover on new work is still all too common.

Inadequate cover can be caused by the improper or careless placement of the steel; or by formwork or steel movement during construction. Despite the general improvement in quality control measures, low cover on new work is still all too common.

Why is Low Cover a Problem?

In a nutshell, the concrete covering the reinforcement protects it from the weather, and helps prevent the steel corroding too severely.

The flip side to this is, the insufficient cover provides insufficient protection. Moisture and reactants reach the steel reinforcing, hastening corrosion. Corroding reinforcement, of course, drives cracking and a cycle of deterioration which leads to ‘concrete cancer’ and the associated expensive repairs.

This is a bit simplistic. There are often several factors working together to bring concrete down – environmental conditions, usage and so on.

Well, can we fix it?

Remediating low cover is a real challenge.

  • Remedial efforts need to blend with the existing concrete.
  • The repair work needs to have the same durability as the rest of the structure.
  • Surface coatings are rarely effective in the long term.
  • Rebuilding or adding concrete cover is usually impractical and costly.

For civil structures with large precast elements, the entire element may be rejected – a very expensive replacement exercise!

And then there’s nanosilica hydrogel treatment …

You’ve quite possibly never heard about nanosilica hydrogel treatment in the context of low cover remediation.

An independent study has shown that reducing the permeability of the concrete by means of spray-applied hydrogel treatment, can effectively double the equivalent cover of the concrete. This is because moisture-borne contamination cannot reach the reinforcing, thus restoring the concrete’s protection.

For example:
If the real cover is 20mm, applying the correct nanoparticle silica treatment will render the concrete’s protection equivalent to 40mm cover.

You can see how significant this is, for remediating issues in the field.

Penetrating hydrogel treatment for inadequate or minimal cover concrete will increase the durability by:

Reducing the permeability (moisture movement) by greater than 100%

This can be equated to an effective doubling of untreated concrete equivalence

Reductions in permeability by hydrogels appear to be significantly greater on concretes of 30MPa compressive strength compared to 50Mpa concrete.

An equivalence factor of 2.0 is recommended as being conservative where cover concrete is insufficient depth and is then treated with a penetrating hydrogel.”

– Murray Gilbertson, G-Group Consulting

This means that hydrogel treatments will make the concrete less permeable, and therefore increase its protective value over the steel.

To be quite clear: This treatment is not a replacement for literal concrete cover in the first place. Low cover is exactly that and can’t be gainsaid. You cannot ‘engineer’ double cover from new, by use of hydrogel treatments. However the treatment can greatly compensate as protection, in the event of a non-conformance.

Practical and Cost-Effective

Spray-applied waterproofing hydrogel treatment is a practical and cost-effective solution to low cover in concrete.

  • Cheaper than other repair methods – and definitely cheaper than replacement!
  • Leaves the appearance of the concrete unchanged.
  • Restores and enhances the planned service life of the structure.
  • Minimal interruption to construction schedules (typical downtime 1 hour).

Faced with low cover issues? Get in touch!

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