Concrete Protection – Act Early!

There is a relatively modern-day tension between costs, construction times, and long-term durability. Structural engineers and mix designers are actively pursuing the ideal concrete mix, to maximise durability and service life, while keeping costs down and not impeding construction schedules.

However, given the broad range of environments, variations in mix ingredients in different areas, and project-specific deadlines and working conditions, there is no simplistic solution which guarantees against premature concrete deterioration in every case.

Concrete deterioration happens whether the concrete is in harsh conditions or not. Even when the structure has a 100-year design life, deterioration still starts from Day 1 – the level of protection you have on the structure determines how rapidly the damage comes about.

Maintenance

Concrete maintenance often gets put off until deterioration is evident. This is a reactive approach to maintenance, and it goes hand-in-hand with the traditional method of doing patch repairs over major damage sites, where the concrete has started spalling and the reinforcing steel is exposed.

Topical maintenance

Maintenance and remediation done on the concrete surface, such as silanes, siloxanes, and even epoxy coatings, are really just a band aid on the structure.

You see, the main reason concrete deterioration happens, and maintenance is required, is because of its inherent permeability.

Concrete is full of pores from the initial cure, when bleed water barged its way to the surface, breaking apart the strands of CSH (calcium silicate hydrates, the bonds between cement particles).

Consequently, moisture that is still within the concrete from curing will move around the structure from these openings, via capillary action. Likewise, water from outside the structure can enter, bringing with it soluble contamination, such as chlorides. This corrodes the reinforcing steel, which in turn causes expansive forces on the concrete around it.

Topical treatments may prevent moisture and contamination from entering, but won’t stop any that is already in the structure from moving around, spreading corrosion to the reinforcing steel or weakening the concrete matrix.

Silanes can penetrate up to 30mm into the concrete, but the depth of steel can be up to 70mm, particularly in marine infrastructure – this means the reinforcing steel would not be protected by that treatment.

And usually, these topical treatments will need reapplication within a few years, and this is costly. Epoxies break down after about 10-20 years, depending on traffic and similar wear. Silanes need to be retreated every 5 – 10 years. They are organic and gradually decompose.

(Side note to both examples of topical coatings mentioned, they can be hazardous to workers applying them, when inhaled or ignited.)

Patch repairs

We might put concrete patch repairs into this category too, except they’re more like skin grafts, and do have a more useful place long-term.

They are still an example of reactive maintenance, when spalling occurs and sections of concrete need replacing. What can go wrong in this case is caused by changes in the anode zones in the parent concrete, due to new concrete being highly alkaline. This is called Incipient Anode Formation (IAF), or Incipient Anode Effect, and it causes the old concrete to start breaking away where the new concrete and old concrete meet.

A mention to Galvanic Anode, or Sacrificial Anode Protection – it can be very effective in preventing corrosion on the surface of steel; however, it can also be troublesome to install in concrete structures, and it doesn’t prevent deterioration through wet-dry cycles via concrete’s porosities. Its application is more useful for large metal surfaces such as found on ships.

Acting Early

Being ‘naturally’ durable, hence the reason it is so widely used, concrete is treated as though maintenance is low priority. And true enough, it can go for many years before corrosion or other deterioration is noticed. However, by the time it has got to this stage, it is a lot more expensive to remediate than protection would have cost initially.

We like to use W. R. De Sitter’s Law of Fives, which outlines that the life of a concrete structure, with respect to durability, can be divided into four phases:

Phase A: Design, construction and concrete curing

Phase B: Corrosion initiation processes are under way, but propagation of damage has not yet begun

Phase C: Propagating deterioration has just begun

Phase D: Propagation of corrosion is advanced, with extensive damage manifesting

$1 extra spent at Phase A is equivalent to saving $5 at Phase B, $25 at Phase C, or $125 at Phase D.

Another way of looking at it is:

$1 not spent on proactive protection turns into

$5 spent on halting corrosion, and minor maintenance,

$25 spent on repairs for major damage, or

$125 spent on replacement.

This is why it is so crucial to have protection, or proactive maintenance, approved and organised for the new structure.

And if you didn't get the opportunity to have protection installed / applied to your asset or infrastructure, now is the next best time.

Effective Protection

Making use of the chance to apply protection proactively? Or even getting in at the early stages of corrosion?

This section applies to both.

Keeping in mind the need to have concrete protected down to the critical zone, the reinforcing steel, you need a treatment that penetrates deep into the concrete.

This is where hydrogel treatments come in – colloidal silica hydrogels, such as the AQURON range, form new, stronger CSH bonds within the pores of concrete. AQURON treatments in particular contain a unique catalyst that is a negative polarity to concrete’s alkalinity. This results in the treatment being literally drawn in to a depth of up to 150mm, protecting the reinforcing steel.

The way the treatment reacts with all available moisture, it becomes a gel in the porosities, the moisture is immobilised, and contamination is halted. By taking away moisture and contamination from the reaction equation, corrosion is also prevented. This treatment is permanent and requires no reapplication. As well as waterproofing the concrete, it results in a harder concrete matrix, along with anti-dust sealing.95% of deterioration in concrete can be attributed to moisture movement within, so you can see how effectively halting moisture movement protects concrete.

This treatment is spray-applied to existing infrastructure, over the entire concrete surface.

However, in new concrete, the treatment can be used as an admixture. This will ensure the concrete is waterproof right through, and even increases mix rheology to make it easier to finish.

AQURON treatments can also be spray-applied to new infrastructure – doing this within the first 72 hours actually achieves the 90% moisture retention required for curing, eliminating any need for a curing compound.

It’s part of the CIVIL-TECT? system for civil infrastructure, although it can be used for warehouse slabs, basements, floor slabs, and more, besides bridges, wharves, and tanks.

Bonus: It prevents Incipient Anode Formation on concrete that has had patch repairs! The whole area should be sprayed with AQURON treatment before and after repairs have been completed.

But remember – maintenance should be done as early as possible. Not just when deterioration is noticed!