It’s well known that strengthening concrete with steel bars results in a combination stronger than either material alone.
It’s also commonly understood that concrete’s high pH (alkalinity) normally provides protection for the steel against moisture-induced corrosion. Concrete’s high pH levels – typically pH 12-13 – will produce a thin oxide layer on the steel, preventing the reaction of the metal atoms. This thin zone is known as a passivity layer or film. It does not actually prevent corrosion, but greatly reduces it. This protective passivity layer can be destroyed, either by reduction of the alkalinity or by an increase in chloride ions.
Alkalinity can be decreased by carbonation of the concrete. This is a very slow process, commonly seen as surface whitening in ageing structures.
Chloride is the better-known cause of concrete corrosion and is a serious issue with marine structures. For reasons not fully understood, chloride ions will penetrate the passivity layer, leaving the steel vulnerable to corrosion. Significantly, only water-soluble ions have this effect.
Key point 1: Reactive contaminants are carried to the steel by moisture.
This is why minor cracking and micro-cracking in concrete, whether by movement, low cover shrinkage, or conditions such as ASR or DEF, is a very real threat.
Key point 2: Minor cracks encourage the penetration of moisture vapour and moisture-borne contaminants.
Here’s where Markham can help.
The application of a penetrating catalytic hydrogel can close the porosity and micro-cracking of the concrete, to a crack width of up to 0.5 mm, and to a treatment depth of up to 150mm!
This depth of treatment ensures the rebar zone is encapsulated. Moisture, moisture vapour, and moisture-borne contaminants, are immobilised.
This is a seriously effective treatment. By capturing the movement of moisture in the concrete, and particularly by treating the concrete early in the deterioration process, corrosion can be arrested or even totally prevented.
If you are in charge of budgeting for the maintenance of a structure, you will see the significance of this at once.
This treatment will help prevent major concrete decay and reduction of the structure’s service life. Think of the savings in maintenance and replacement costs!
Talk to Markham today about adding life to the concrete structures in your care.