Let’s start at the start!
What causes Concrete Cracking?
Concrete can crack in a whole lot of ways. Surprisingly, much of it is related to chemical failure!
Physically, cracks can form due to structural movement. If the concrete flexes and is subjected to unplanned or excessive tensile pressure, cracks are likely to open.
However, even without stress from structural instability, unless the concrete is sealed internally and externally, corrosion is almost always active. This is because moisture is actively moving within the slab/structure, transporting foreign contaminants that are harmful to the reinforcing steel.
These corrosion mechanisms include expansive reactions such as DEF and ASR, surface decay such as carbonation, and ingression such as chloride attack.
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With all of these examples, the worse they get, the faster they get worse, so deterioration increases in a rapidly accelerating cycle. They are progressive, though, and generally aren’t noticed in the early stages.
Concrete Heals Naturally
Through a slow and unguaranteed process, most concrete can heal itself ‘naturally’, due to ongoing hydration of clinker minerals such as free lime, or carbonation of calcium hydroxide (Ca(OH)2).
Atmospheric water and carbon dioxide enter and react with available cement particles that haven’t been used in curing. The reaction forms additional C-S-H bond strands, similar to the initial curing of concrete. This process is limited, extremely slow, and uncontrollable.
Boosting this process
Applying nanoparticle silica with a suitable catalyst to concrete results in a reaction with the concrete’s moisture and natural alkalinity, creating C-S-H in a hydrogel form.
A catalyst in the treatment reacts with the opposite polarity of concrete, so it is drawn into the concrete very effectively in any direction, not by gravitational means. More about that in this article.
This hydrogel eventually becomes part of the concrete, but it is denser than the original concrete. Like the process of concrete healing itself without external treatment, applying AQURON colloidal silica uses the concrete’s available resources, but AQURON treatments work much faster than ‘natural’ healing. The colloidal silica, which immobilises the moisture into a gel, prevents water movement in structures, even before the C-S-H strands have been duplicated.
This is why hydrogel treatments are utilised for concrete remediation: it has been proven that using AQURON is much quicker and more reliable than waiting for the concrete to heal itself.
A notable example of this principle in practical action was a basement at Canterbury University, Christchurch, NZ. An unexpected failure of the existing waterproofing system caused the basement to leak, with water seeping through microcracks. AQURON treatments were applied to seal and heal these cracks, thereby waterproofing the concrete. The basement is in active use 20 years later.
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Crack size
So what are the capabilities of hydrogels in filling cracks?
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The colloidal silica treatments are guaranteed to fill gaps up to 0.5mm wide (see the image above). You may think, then, that gaps larger than 0.5mm are unsealable by AQURON; however, this is not the case. Because the crack tapers, somewhere in its depths, the width of the crack will get down to half a millimetre; the crack up to this depth will be filled (see image below).
Larger cracks can be sealed by silicone injection. Hydrogel treatment is still recommended to fill microcracks and porosities in the existing concrete and to address the underlying problem of internal reactions.
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Structural Movement
If a structure is unstable and actively moving, cracks will continue to grow. Physical force being exerted on the infrastructure by movement indicates a more serious problem, and the structural integrity of the infrastructure should be assessed.
Completely compatible
Colloidal silica hydrogels are suitable for the remediation of all concrete types and uses, as the treatment does not add properties to the structure that are not already present in concrete. This means that after AQURON has been applied, you will still be able to apply any treatment as you normally would, such as anti-graffiti, tinting, render, and so on, because the colloidal silica is fully compatible with concrete.
What this also means for the structure’s safety is that treating the concrete with hydrogels does not introduce any foreign contaminants that could corrode the reinforcing steel.
Interested in speeding up the healing process? Talk to one of our team!
