Concrete in mines – and corrosive chemicals.

Concrete just does not get along well with reactive chemicals. As a mining asset manager, how do you protect concrete from harsh chemicals such as acids?

?

Washdown bays and processing areas use a number of acids and cleaning compounds, which by their nature are highly reactive – this suits the purpose at hand, but they are hazardous for concrete service life. Concrete replacement time in mineral processing facilities comes around a lot quicker than most other sites – including the marine sector.

?

Quoting Doug Hamlin from a brilliant Invisible Strength podcast – “There’s many different attack mechanisms, things like that. But I guess in the main, the premature deterioration of concrete structures is really the most expensive in terms of asset management of concrete structures, concrete assets. So that’s their structures that have been designed and constructed with the, you know, 50 or 100 year design life. They’re getting to, you know, maybe half that and starting to show signs of deterioration.”

The need is chemical resistance for concrete.

But how do chemicals actually attack concrete?

Acids and solvents have different ways of eating away at concrete, and even causing reinforcing steel to rust. This then escalates quickly to spalling, where large sections of the concrete fall away, and reduce structural integrity. But whether it’s concrete or steel being attacked by chemicals, one thing is common to both:

"...95% of the issues associated with concrete, can be tied back to the fact that it lets moisture migrate through it."

So what is an effective way to prevent contamination within the concrete matrix?

?

Increasing impermeability is key - preventing movement of moisture through the concrete matrix. But concrete is a solid block – how can you get inside it?

The best time is definitely during construction – when the concrete is being batched, a waterproofing admixture is one of the most beneficial ingredients for increasing durability. (Be careful here - some crystalline admixtures can result in shrinkage issues due to being activated by absorbing moisture that should be used for curing.)

But for concrete that has set – existing concrete, where you don’t have the opportunity of adding an admixture – it is still very achievable to seal the concrete internally. Concrete is like a hard sponge; just as moisture can enter, so can other treatments. Colloidal silica can be spray-applied to the surface, and is drawn in to 150mm deep with catalytic reaction.

See image below, where the colloidal silica (marked in red) surrounds the reinforcing steel – the critical zone of concrete.

The treatment then reacts with the moisture inside the concrete to form a hydrogel – this gel arrests all contamination underway, and blocks moisture from entering. The gel eventually becomes a part of the concrete itself, and the concrete matrix - the hard sponge - becomes denser, more impermeable.

What a great method of keeping the harsh chemicals from reacting with concrete!

Contamination control in concrete is critical. Resisting the aggressive action of acid increases the service life of concrete, and reduces the need for so much maintenance.

This is not a topical sealer – as such, it does not wear away like a topical coating.

?

Have a look at the system that MARKHAM has used for a number of mines, wastewater treatment plants, and marine structures! It’s the CIVIL-TECT system, which can be tailored to the project-specific requirements.

?

This is an effective way to reduce maintenance costs, and lengthen out the replacement time - saving the company on Capital Expenditure long term.

More projects that used the CIVIL-TECT system for extending?the service life of concrete (click the image to go to the project page).