Let’s start at the start!
What causes Concrete Cracking?
Concrete can succumb to cracking in a whole lot of ways. Surprisingly, much of it is related to failure chemically!
Physically, the cracks can be formed by movement of the structure. If the concrete flexes, and is put under unplanned or excessive tensile pressure, then cracks are likely to open up.
However, even without stress from structure 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 corrosions include expansive reactions like DEF and ASR, surface decay such as Carbonation, and ingression such as Chloride attack.
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).1
Atmospheric water and carbon dioxide enter and react with available cement particles that haven’t been used in curing. The reaction creates more C-S-H bond strands in a similar manner to the initial curing of the concrete. This process is limited, extremely slow, and cannot be controlled.
Boosting this process
Applying a nanoparticle silica with a suitable catalyst to the concrete results in a reaction with the moisture and the natural alkalinity of the concrete, and 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 denser than the original concrete itself. Like the process of the concrete healing itself without external treatment, applying MARKHAM colloidal silica also uses available resource within the concrete, but the treatments work much faster than ‘natural’ healing. The colloidal silica which immobilizes the moisture into a gel (“hydrogel”) 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, because it is proven that using MARKHAM colloidal silica hydrogel treatment is much quicker and more assured than waiting for concrete to heal itself.
A notable example of this principle in practical action was a basement at the Canterbury University, Christchurch. Unexpected failure of the existing waterproofing system caused the basement to leak, seeping water through micro-cracks. Hydrogel 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?
The colloidal silica treatments are guaranteed to fill gaps up to 0.5mm in width (note image above). You may think, then, that gaps larger than 0.5mm are unsealable by hydrogel treatment; 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 the micro-cracks and porosities of the existing concrete, and to fix the underlying problem of internal reactions.
Structural Movement
If a structure is not stable, and is actively moving, then the cracks are going to 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 known to be suitable remediation for all concrete types and uses, because the treatment does not add any property to the structure that is not already found within concrete. This means that after treatment has been applied, you will still be able to apply any other treatment as you normally would, such as anti-graffiti, tinting, render, etc. because the colloidal silica is fully compatible with concrete.
What this also means for the safety of the structure is that treating the concrete with hydrogels is not introducing any foreign contaminant which would corrode the reinforcing steel.
Interested in speeding up the healing process? Talk to one of our team!
1 https://www.sciencedirect.com/topics/engineering/self-healing-concrete
