Resisting chemical attack on concrete

Softwater, waste water treatment, marine conditions and other reactants hazardous to concrete

Concrete is a very versatile construction material, and as a result is used in almost every working environment.

Some working environments contain substances which are innately harmful for concrete, and actively accelerate the deterioration process. These include soil, sewage and associated treatments, food (particularly sugar and sweet liquids), agricultural chemicals, animal liquids (such as blood and urine), or waste materials.

Further, some moist environments are conducive to invasive plant and algal growth.

This factor itself indicates moisture control is required.

All of this is unhealthy for the concrete matrix, and the moisture is key in this conversation.

Why?

Concrete is like a hard sponge. It's innately porous from the initial cure, where bleed water carved its way through to the surface.

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

Contamination is transported through these porosities - or capillaries - via moisture movement. The 'contamination' could be chlorides from marine environments, harsh cleaning chemicals in mines, bio-fluids in healthcare facilities and meat processing factories, and solids that are soluble - like the sodium from salt in bulk storages, or phosphates and sulphates from agricultural fertilisers.

When this contamination comes in contact with the reinforcing steel, eventually major corrosion will set in. The ions in certain elements corrode steel when they come in contact, as well as the oxygen itself that is carried by the moisture. When the passive layer of rust on the steel surface breaks down, rust develops more rapidly.

This will cause expansive cracking in the concrete due to pressure from within concrete matrix, followed by spalling.

Aside from the reinforcing steel...

The surface of concrete is durable enough to face abrasive elements (including wind and water erosion), but obviously this does wear over time, and the same applies to chemical resistance.

Certain chemicals dissolve cementitious materials, and these are not just artificially formulated (such as concrete cleaning solutions).

For example, sulphate attack (from water containing magnesium sulphate) is a reaction with the calcium silica hydrate formations in concrete, and turns concrete into powdered mass.

This can be found in soil or groundwater.

Soft water attack (from groundwater containing low dissolved ion content) leaches the calcium hydroxide (portlandite, Ca(OH)2) in the hardened cement matrix.

This proves that the concrete itself also suffers, as well as the reinforcing steel.

Can this be prevented?

The next question is, Can the whole concrete structure be protected or remediated cost-effectively?

A pertinent question, considering the amount of concrete under attack in structures like bridges, wharves, and tanks. Huge warehouse slabs face the same difficulty - the area to treat is not just a small patch.

So firstly, treatment that's going to last will give the biggest advantage in maintenance works.

Secondly, quick and effective applications will be needed to ensure minimal downtime.

What treatment will last?

At MARKHAM , we've found that using a very effective treatment for filling the porosities, and increasing the concrete's impermeability, will benefit practically in many ways.

At the same time as making the concrete impermeable, the treatment reacts with the moisture to turn it into a gel and immobilise it. Thus, all contaminants are halted.

This treatment is a colloidal silica hydrogel.

Using a catalytic reaction, the treatment is drawn into the concrete to a depth of up to 150mm. By reacting with the moisture, and uncured calcium, it forms Calcium Silica Hydrate strands in the porosities, just the same as when the concrete cured originally but stronger.

This effectively waterproofs and seals the concrete, preventing all further moisture movement. Corrosion is halted, as well as any further deterioration associated with moisture.

Above: Invercannie Water Treatment Works Supernatant Tank, treated with hydrogels

This system will extend the service life of structures by many years. By the same practise, long-term maintenance is reduced, and associated costs.

Downtime involved

With the AQURON colloidal silica hydrogel treatments MARKHAM uses, these are spray-applied with wet-on-wet coats. This allows us to apply them to entire structures in a relatively short time - and the treatment concrete is trafficable after just 1 hour. It's an efficient means of protecting copious amounts of concrete, rather than requiring a 24-hour shutdown for a small bridge or wharf deck. In the case of operational sites, the quicker the concrete is ready for use, the less the shutdown costs.

Environmentally-friendly?

Obviously over-spray would be a concern, especially in marine environments and water treatment tanks!

The AQURON treatments have been certified as safe for around in potable water. They are also Nil-VOC, and is non-toxic. This makes it ideal for municipal water supply infrastructure.

Bonus, the treatment contains nothing that is not already found in concrete, so it won't have any negative effects on the concrete itself.

The system called CIVIL-TECT® was developed by MARKHAM and utilises the colloidal silica hydrogel treatments - it's aimed at wharves, bridges, tanks, and more... any civil infrastructure with unprotected concrete.

It involves 1 supplier, 1 installer, and 1 project-specific warranty, all organised by 1 team.

Have a look at it for your own project or asset! It definitely saves stress and costs in the long-term.