by Daniel Green
Steel. It’s one of the most durable, workable, and abundant minerals on the planet. And with a service life of hundreds of years and a relatively low cost, it is no surprise that this mighty material usage is so common in construction. It’s not all sunshine and rainbows, however. Everything has its foibles. In the case of steel, it is corrosion.
Tarnish. Patina. Abrasion. The dreaded tin worm. Whatever name it goes by it always ends in the same way: disintegration. Interestingly enough there’s actually more than one type. You might want to take a deep breath for this one because; the most common variant is the result of iron and iron derivatives, when they are in exposure to oxygen and moisture, especially in a cyclical or repetitive manner, resulting in an outcome where the base metal becomes oxidised. What a mouthful!
Essentially steel that lives in normal air gets wet, then dry, then wet again and it decays. The air and moisture enter the steel at a cellular level, forming a by-product known as hydrous iron oxide, aka rust. Anyone with a classic car will know it very well! Unfortunately for us construction professionals the entire planet is either humid or oxygenated or both, meaning almost no matter where there’s steel – there’s rust.
Environmental factors can also increase the rate of corrosion exponentially. Some of these are great variances in daily temperature and humidity levels [the cycle of wetting and drying], the presentness of chemicals [both natural and man-made], metallurgic stresses, and fatigue [which can compromise coatings and allow moisture and air into the base material], bacteria, dirt [which holds moisture], coatings or lack thereof, proximity to the ocean and many others.
Slow and Steady
As iron oxide burrows itself in, it causes delamination of the base material, fracturing it off in flakes. Relatively speaking, this occurs extremely slowly meaning there is a good chance to catch it in time. However, if left unchecked, eventually there will be no steel remaining and if that steel is structural – no building. There are many factors that decide the rate of corrosion as well as the extent of it, but delamination via oxidisation is the most common outcome.
Better Than Cure
Yes, this is a remediation article but prevention is the best outcome so let’s start there. Adding other elements during manufacturing can slow or even prevent corrosion by turning the steel into an alloy. Elements such as molybdenum, titanium, chromium-vanadium, manganese, and nickel. In this case, the resultant product is stainless steel. It is an almost flawless solution, however, most of the time this is cost-prohibitive. The more common approach is to coat the steel in other materials to stave off corrosion.
Galvanisation is the process of using a zinc-rich product that attaches itself to the steel. The appearance is that of dull and dirty aluminum, so it won’t win any awards but it is extremely effective at rust prevention. The downside is that at any contact point of mechanical friction the gal will eventually wear away.
Coating with suitable primers and paints will protect iron products for decades. Just take a look at vehicles. They are long-lasting, inexpensive, and easy to apply.
Powder Coating uses a special loose-fill product, blowns it onto the steel and then baked to cure.
Electroplating involves using electrolysis to coat the base metal in another element that will protect from corrosion far better than raw steel. Some of these are chromium, zinc, or even aluminum. It differs from galvanisation in that gal coating is much like battering a piece of fish whereas plating involves electrical fusion.
Oiling is the cheapest solution, though it does require frequent effort. It does not mix with water, so it will repel moisture to the point of corrosion protection. It may not be pretty but it works.
Remember, rust occurs in the presence of oxygen and moisture. If you deny the metal one of those it simply cannot corrode.
This is all well and good if you’re in the construction phase. What if you’re the poor sod dealing with steel construction sins of the past? All is not lost. Steel remediation is an absolutely effective solution to structural members under the influence of corrosion.
The Hard Questions
The first step is to find the impetus for the corrosion. This may not be as straightforward as you might think, especially if:
a] there are numerous factors that could be at work
b] the corrosion is not at the surface level where it can be easily assessed.
Different faults will produce different outcomes and so steel remediation needs the expertise to pinpoint the source.
For example, all signs may point to a leaking water pipe when in reality the nearby ocean caused that moisture. Concrete cancer may be the result of poorly prepped steel reinforcement or it could be because the mix had too high a sand content. In either case, remediation expertise will be able to lock down the cause and then work out the most effective solution.
Once the cause has been pinned down, all damage must be fully exposed. If you, the owner are at the stage of approving remedial works then the damage has already been done and there is no point in half measures. It is an all-or-nothing approach. Sometimes, major construction works need to occur to expose the full extent of the corrosion. Much like surgery, often the entire picture cannot be appreciated until you have ‘gone in’.
Face Your Fears
With the damage fully exposed, the corroded steel must be dealt with. If structural integrity calls for its existence then it must be replaced with equal or stronger material. If the damage is not so deep as to warrant replacement, the steel must be returned to its pre-corrosive state via mechanical or chemical cleaning. It must be what we refer to as ‘bright’ before further remedial works can continue.
Once we repaire and/or replace steel, it must have corrosion prevention measures applied to it or the same damage will simply occur again. There is an entire market dedicated to in situ corrosion prevention via easily applied products. They can be quite expensive but compared to the cost of demolition and reconstruction they’re likely very cheap. Now is the time to apply those coatings.
Once this is complete further remedial works can continue to return the building to its former purpose – concreting, carpentry or cladding, and so on.
Due to the complex ways in which steel has been used, when it goes awry its remediation calls for specialised knowledge and experience. Making the same mistake twice could prove very costly indeed.
For guidance in structural steel remedial works contact Tom at Perfect Remediation and Refurbishment on 0407 491 888.
For more information on our services, take a look at our webpage or request a free quote.contact us today