Ammonium Nitrate: Used both for growth and sudden destruction

It can also destroy concrete slowly but surely.

Ammonium Nitrate? What is that?

“Ammonium nitrate is a chemical compound with the formula NH₄NO₃. It is a white crystalline salt consisting of ions of ammonium and nitrate. It is highly soluble in water and hygroscopic as a solid, but does not form hydrates. It is predominantly used in agriculture as a high-nitrogen fertilizer.

Its other major use is as a component of explosive mixtures used in mining, quarrying, and civil construction.” – Wikipedia (‘Ammonium nitrate’ entry)

Agriculture. Mining. Quarrying. Civil construction. There must be a lot of this stuff in storage waiting to be used.

What is the threat to concrete?

“As is well known … ammonium nitrate solutions are very corrosive to cementitious materials, which leads to dissolution of cement-based materials…

It is clear from the above-mentioned chemical reaction that the ammonium nitrate decalcifies the hardened cement paste due to removal of calcium hydroxide…

This results in decalcification and dissolution of other products of the hardened cement paste and leads to a reduction of the pH-value. Consequently, steel reinforcement corrosion may occur at an accelerated rate.” – ScienceDirect (‘Deterioration of high-performance concrete subjected to attack by the combination of ammonium nitrate solution and flexure stress’, U.Schneider & S-W. Chen)

So there you have two deterioration mechanisms:

‘Removal’ or leaching of calcium hydroxide, which robs the concrete of parts of its C-S-H molecule.
Steel reinforcement corrosion occurring at an accelerated rate. And that, as we know, leads to major cracking and spalling of the concrete.

What is the answer?

There are a number of suggestions for new construction – in particular, reducing the permeability of the concrete in various ways.

Importantly, chemicals need moisture to enter the concrete, and to facilitate the reactions once inside the concrete.

Ammonium nitrate is used for fertilizer and explosives

Block the carrier.

Concrete is not perfectly waterproof in and of itself. Despite the common addition of flyash or other fines, bleedwater porosities will occur during curing. Unless you have included a self-healing agent in the mix, those porosities guarantee the concrete will still accept moisture ingress. That moisture, as noted, is the carrier of the aggressive reactants – in this case, ammonium nitrate.

And here, for new construction, we submit CONQOR B50 waterproofing admixture. CONQOR B50 admixture is produced from a byproduct of the geothermal industry. It protects against chemical attack by converting the leachable calcium hydroxide into a hydrogel, not allowing it to react with the ions which normally react with the calcium hydroxide and create an expansive force in the concrete.

Removal of calcium hydroxide reduces the risk of attack. Alongside this, because the concrete is waterproof, it limits any attack to the top surface – the internal matrix is protected.

Further, we recommend coupling this together with spray-applied AQURON 7000 as a curing and durability hydrogel treatment. This ensures the critical curing phase is taken care of, and proper hydration takes place giving a higher quality concrete, as well as secondary waterproofing as a belts-and-braces approach against sulphate attack.

Can this approach help existing concrete?

AQURON 7000 is a real friend even for aged concrete. The treatment penetrates around 150mm into the substrate, regardless of gravity, and arrests the reactivity occurring deep inside the matrix. By immobilizing the moisture, the reactions are robbed of their food and drink, and cannot extend. This means effective protection for the reinforcing steel.

Real projects, real answers.

But you’re wondering how all this applies to your concrete – the infrastructure you’re in charge of – not to mention your schedules and budget. You will be pleased to know these treatments are outstandingly practical.