What is ‘Low Cover’, in the Context of Concrete?
“Concrete cover, in reinforced concrete, is the least distance between the surface of embedded reinforcement and the outer surface of the concrete.”
‘Low cover’ refers to the insufficient distance between the concrete surface and the reinforcement. Unfortunately, construction timeframes are shrinking. 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.
Why is Low Cover a Problem?
Critically, the concrete covering the reinforcement protects the steel reinforcement (rebar) from environmental effects, preventing its corrosion.
The flip side to this is, the insufficient cover provides insufficient protection. The inadequate or minimal cover is directly related to premature deterioration of the structure.
Early cracking can be caused by plastic settlement cracking due to the proximity of the steel to the surface, and cracking over time can be caused by corrosion of the steel due to the lack of protection. Either way, concrete cracking sets on an accelerated deterioration cycle leading to premature decay of the structure.
What Possible Solutions Exist?
Rectification of low cover is a real challenge. Remedial efforts need to blend with the existing concrete, and 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 AQURON …
You’ve quite possibly never heard about AQURON 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 AQURON 2000 – Sustainable Internal Concrete Waterproofing Sealer or AQURON 7000 – Sustainable Concrete Corrosion Protection for Existing Structures 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.”
Practical and Cost-Effective
Spray-applied AQURON 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!
