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Problem Concrete

What goes wrong? and can we fix it?

Problem Concrete
01 December 2020 Posted in

It’s a dreaded ‘n’ word on any construction site or precast yard … non-conformance!
 
We can’t touch on all the negative possibilities! Human error plays a part in many preventable but random construction issues.
We’d like to talk about several concrete issues which seem to keep happening – and what may be possible to rectify the situation.
 

Early Cracking

There are two leading causes for early cracking in new concrete: shrinkage cracking, which relates to curing and hydration; and plastic settlement, which we’ll discuss under ‘low cover’ later in this article.
Lesser causes include honeycombing and poor compaction.
 
Prevention is better than cure, of course, but what to do when you’re faced with a finished slab or precast element which shows distinct cracking?
You’re going to tell me this is a very common occurrence, and it’s not worth worrying about in 9 out of 10 cases. Not so!
 
Early cracking opens the gates to the entrance of contamination into the concrete. By contamination, we mean reactive substances, carried by moisture, which in turn will trigger failure mechanisms within the concrete such as ASR or steel corrosion. Once those mechanisms are operating, a cycle of deterioration sets in, and the concrete is doomed to premature deterioration and reduced service life.

Pro-active Response

The sooner you take action, the less it will cost in the long run and the better the outcome.
Genuine hydrogel treatments for concrete, induced by catalytic silica, can seal cracks up to 0.5mm, and enhance the concrete’s self-healing qualities.
Penetrating deep into the concrete itself, they use the existing moisture within the concrete, generating more of the C-S-H which naturally gives the concrete its strength. Aquron hydrogel treatments boost durability!
 

Low Cover

This just isn’t supposed to happen, is it? Whole bridge beams or structural elements rejected due to insufficient cover of the reinforcing – what went wrong?
 
It’s not necessarily raw human error in the placement or pouring. Things do move around as the mix is introduced and compacted, and the reinforcing sometimes simply doesn’t stay exactly where it is put. Combine this with small error margins, and you’re faced with a reject.
Plastic settlement cracking can be an obvious early sign of this issue.
 
Honeycombing is somewhat related to this same problem.

Aquron concrete hydrogel treatments can remediate low cover issues

It’s All About Impermeability

The reason minimum coverage limits are set is to ensure maximum protection of the steel by the concrete. This comes back to moisture-borne contamination again, where shallow placed reinforcing is put at risk of corrosion due to moisture entrance.
The answer to the quandary, then, is to make the concrete more impermeable. If you can prevent the entrance or movement of moisture in the concrete itself, you are protecting the steel as if it were covered with more concrete.
 
Hydrogel treatments to the rescue! Close the porosity, immobilise the moisture, increase the impermeability – and you’re doing the work of the missing concrete.
Aquron hydrogel treatments can actually double the effective cover of the concrete, and that’s a conservative estimate.
This can be a major save in the rushed schedules of a precast yard – no need to discard large and expensive concrete elements due to low cover issues, they can be deemed conforming.
 

Hidden Threats

Occasionally a high-volume precast element will be rejected because its internal curing temperatures exceeded 70°C, or a similar given limit.
 
The reason for this is that while the concrete itself is generating heat while curing, these high temperatures prevent even hydration. The result is that unused cement and lime remain within the concrete.
Later in the life of the structure, and triggered by ambient moisture, these substances can re-start a fake curing process, forming clusters of ettringite within the concrete.
This is called Delayed Ettringite Formation (DEF) and can induce significant cracking of the concrete as it works it way through the element.
 
Another built-in failure mechanism is called Alkali Silica Reactivity (ASR) and is caused by contaminants brought in with the aggregate. Later introduction of moisture generates a deleterious expansive gel which opens up cracking from within.
This is rarely identified at the construction stage, but may be discovered by testing the aggregates used.

Did You Notice We Mentioned Moisture?

There it is again. Moisture movement into and through the concrete will trigger these internal reactions.
The answer is to close the porosity and immobilise the moisture – turn it into a hydrogel using Aquron concrete treatment.
 
Intrigued?
Like to talk about your own particular concrete issues?
Get in touch with our friendly team! We’re experienced and practical, and may well be able to save a situation for you.

A Couple of Caveats

1: Hydrogel treatments may not be the sole answer.
You may be experiencing advanced corrosion or spalling. Hydrogels can be a valuable part of an overall repair approach, but they are not a substitute for cementitious fillers or replacement steel if those are needed.
 
2: Every project is different and must be assessed as such.
And part of our team experience is that we are risk-averse. If we can’t help you, we’ll be honest and say so, and do our best to direct you to someone who can.
 

Markham concrete durability treatments

Header photo by Inny Kwak on Unsplash



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