MODERN CONCRETE AND DURABILITY ISSUES
There’s a lot of research on the ancient Roman concrete, solid examples of which stand to this day. During 2017 there was a good deal of excitement at the newly-published discovery that Roman concrete actually grows stronger as it ages, and it withstands seawater naturally. These effects are apparently caused by specific volcanic materials included in the mix – substances which are not commercially available to most of us.
The other rare commodity in the modern world of construction is time. Time is money, and this results in schedules being squeezed to a minimum wherever possible. For concrete, this often means that curing time is minimal. Unfortunately it also means that placement may be rushed, resulting in uneven cover and other issues.
(Low cover is something the Romans never needed to worry about … steel hadn’t been invented, and their concrete did not use internal reinforcing)
KEY POINT: There’s a clear link between cracks in concrete, and the deterioration cycle.
More on this later – but here’s something to think about.
One major Australian premix company lists four main factors as causes of concrete cracking at construction:
- Construction and supervision problems – approx. 36%.
- Design defects – approx. 27%.
- Ambient conditions (temperature, humidity, etc.) – approx. 21%.
- Quality of materials – approx 17%.
Is it any wonder modern concrete isn’t lasting as long as the Roman experience?!
OKAY, SO WHAT CAN WE DO ABOUT IT?
Concrete needs protection.
For risk mitigation, and to preserve the intended service life, concrete needs treatment over and above its mix design.
Early hairline cracking is commonplace, and becomes a gateway to reactive contaminants.
Exposure to the weather can also lead to the entrance of contaminants, due to the porosity of the concrete.
There’s a lot of valid discussion on impermeability in this connection, but the bottom line is that it’s impossible for commonly used mix elements to provide total impermeability. The process of curing itself will open up bleedlines in the slab as excess moisture rises. These leave cavities which become avenues for moisture ingress later.
These contaminants can induce deterioration of the concrete itself, but more commonly invade the reinforcing zone and set up conditions for corrosion of the steel. Corrosion is expansive and causes greatly increased cracking. This in turn becomes a cycle of deterioration, with more contamination entering the concrete. Delamination and spalling result, ultimately contributing to structural weakness or failure.
KEY POINT: Reactive contaminants are carried by moisture.
Chlorides, nitrates and other contaminants cannot ‘travel’ in dry form – they are transported when dissolved in water (including water vapour).
IMMOBILISE THE MOISTURE – PROTECT THE CONCRETE
The solution is so simple, it’s hard to believe. If you can stop moisture entering the concrete, or moving about within it, you rob any deterioration of the elements it feeds on.
This touches on the point of permeability, as noted above. To truly make the concrete impermeable, its internal porosity matrix must be blocked.
The moisture immobilization stars … concrete hydrogel treatments! A hydrogel formation can be induced in concrete by introducing colloidal nano-particle silicate. This reacts with free limes and moisture within the concrete to form a gel which occupies the porosity and closes the bleedlines.
If applied early, the hydrogel can form during the curing process, greatly enhancing curing quality and minimizing shrinkage.
Immobilizing moisture prevents contamination moving about in the reinforcing zone, protecting the steel.
Closing the micro-cracking helps arrest the whole deterioration cycle.
HYDROGELS ARE BENEFICIAL FOR –
- Enhanced curing with minimized cracking.
- Deep sealing, with anti-dusting hardening.
- Proactive maintenance – both protection and remediation.
Looking at the long-term maintenance costs of a given structure – hydrogel treatments are extremely cost effective, helping reduce maintenance which would otherwise be required due to deterioration, and helping to maximise the planned service life of the structure.
CONCRETE NEEDS PROTECTION!
With apologies to all engineers and mix designers up front – unprotected concrete is unlikely to achieve its planned service life by itself. The dice are loaded against it.
Cost-effective long-term protection is possible – and should be included!