Corrosion Matters

At CSI we have growing concerns about the country-wide checks that are being conducted for corrosion on concrete elements in buildings and infrastructure.  While we are sure there are some operators undertaking some very thorough investigations, we do come across buildings and infrastructure that are given ‘visual inspections’ only. In these instances, we have been convinced more testing is necessary, as it is a highly specialised field.

CSI Ltd recently had the opportunity not only to talk with Australian infrastructure owners about their programs for corrosion control (particularly in respect to marine structures),  we also attended a presentation by the Australasian Corrosion Association and received the same message from both groups.  Here in New Zealand, we should be taking it very seriously and comprehensive checks and testing should be employed.  If corrosion is left undetected and unmanaged it will eventually weaken a structure until it is seriously compromised in terms of strength, and therefore a danger to users.  No repair methodologies should be considered or recommended until it is fully understood what is causing corrosion

CSI offers a six-point testing plan to establish the cause of corrosion:

1. Visual inspection – looking for obvious signs of delamination, spalling, honey-combing and discolouration from steel corrosion.
2. Acoustic sounding – using a hammer we listen for a hollow sound from the concrete, indicating delamination and checking for voids.
3. Concrete reinforcement cover – using scanners we can check the amount of concrete that is covering the reinforcing steel.
4. Chloride content test – checks for depth of chloride contamination in the concrete (chloride puts the steel at greater risk of corrosion).
5. Carbonation of concrete – depth of carbonation in the concrete identifies the amount of risk of steel corroding.
6. Rebar corrosion determination – this is half-cell potential testing (which identifies the corrosion potential of the steel).

While all of these tests are not required all of the time, it is worth moving from visual inspection to at least one other ‘backstop’ test to ensure what you are seeing can actually be verified.  In general, as you move through the testing, you will discover whether the other tests will be necessary.  Please see our Services page for a description of CSI Corrosion Surveys.

The Australasian Corrosion Association have the following blog post on their website encouraging infrastructure owners and engineers to promote: “Proactive asset management of concrete infrastructure”.

Monitoring the impact of corrosion on concrete infrastructure such as storage sheds, wharves and bridges is a critical aspect of ensuring structural integrity and durability performance.  Their blog discusses key ways to minimise corrosion and the impact it can have, we’d encourage you to read their full blog post here.

In NZ there are examples of infrastructure being urgently closed because when long overdue corrosion surveys were undertaken it was evident the bridges were a great risk to users.  Eventually this infrastructure will have to be condemned or rebuilt at great expense.  The extent of the inconvenience and cost could have been greatly mitigated by early corrosion detection.

Harsh environments — especially coastal (like New Zealand), tropical or desert areas with high salt levels or extreme temperatures — can accelerate the rate of corrosion of steel in concrete. Usually, the most exposed elements deteriorate first but it may take 5 to 15 years for the effects of reinforcing steel corrosion to become visibly noticeable.

This is supported by the paper below, of which we have presented a snippet from The Australian Corrosion Association blog and the full paper is well worth a read.

“Corrosion losses are measured for a variety of research, safety, and economic reasons. The techniques employed may be classified in many ways although the most basic distinction is between physical measurements of material present and the monitoring of reaction dates. The former is typified by ultrasonic of radiographic techniques or possibly direct measurements of weight loss or pit depth. Less direct methods may utilise a change in vibration frequency of a corroding reed, count rate variation of a corroding layer, change in resistance of a corroding wire, strip or tube, measurement of evolved gas or even concentration of corrosion-produced ions“.

1991 Paper: Corrosion Monitoring For All Or Why Should I Measure Rust?

There is plenty of research and evidence available to show that the ‘silent cancer’ of corrosion should not be left ignored or brushed over.  Corrosion can often be stopped in its tracks if caught at every site it exists and early on in the process.  There are also now a large range of corrosion control techniques, one of which can be found on our website.

If you’re concerned about corrosion then call in an expert.  CSI can assist you with independent, accurate and nondestructive corrosion analysis testing of your building or structure. Drop us a line directly via email or phone 0800 33 7767.