Advice on galvanizing
Hot dip galvanizing applications
Hot dip galvanizing in Italy and Europe
The construction market represents the largest share of production of hot-dip galvanized material. Alone it represents more than 40% of the total. The range of hot dip galvanizing applications in both public and private buildings is almost infinite. All structural components can be galvanized, from steel beams of all types to rods for reinforced concrete. In this way, galvanizing can be used in the construction of all residential and non-residential buildings, bridges, airport structures, railway stations, subways, car parks, stadiums and sports facilities, hotels etc.
In addition to the aforementioned applications, galvanizing is also carried out on finishing items such as balconies, railings, steel balustrades, gates, iron shutters, external stairs and fire exits, gratings, gutters, curtain walls, the ornamental steel used for the construction of certain fences or gazebos and roofing of terraces, pergolas and articles of aesthetic value such as certain lanterns, tables and chairs, benches … valuable protection.
Even in the industrial building sector, where one opts for the lightness and versatility of steel structures, protection is very often entrusted to galvanizing, except in those cases in which there is high aggressiveness due to the presence of pollutants in considerable concentrations, in especially acids. Generally, it is possible to deal with aggressive environments with the application of the duplex system, galvanizing and painting, with an appropriate choice of the chemical qualities of the paint in relation to the type of atmosphere. However, there are environments in which galvanizing is not recommended, such as with structures exposed to the risk of acid condensation or contact with strongly alkaline substances. Moreover, in those cases, the use of carbon steel itself is highly risky. The construction sector is both the main galvanizing market but also the field in which there are the greatest opportunities for expansion. In fact, every year, only a small percentage of the structures and artifacts intended for construction that could be effectively protected from corrosion with galvanizing, are actually galvanized.
Research conducted in recent years in Italy has estimated the galvanizable steel that actually reaches galvanizing at around 8%. The rest is protected with alternative methods which unfortunately do not guarantee the same performance. This is essentially due to two fundamental reasons, poor knowledge of the characteristics of the treatment, which require specific knowledge in the functioning of anti-corrosion systems and poor economic evaluation. The following chapter is aimed at debunking certain unfounded convictions in the evaluation of the economic convenience of galvanizing.
The galvanizing of the rod
A particular application of galvanizing in the construction field is the protection of reinforcements for reinforced concrete. The high alkalinity of the cement present in the concrete leads the steel to form a thin oxide film, passivating itself and, therefore, preventing rust from attacking it. This happens for a young concrete, which retains its characteristics for a few years after casting. However, there are frequent conditions in which this corrosion protection loses its effectiveness over time or cannot be established to an adequate extent (see also chapter 3).
This is the case, for example, of the presence of defects in the cement, such as cracks, tears, gravel nests, excessively reduced or missing cement coatings, of the carbonation of the cement or of the effect of chlorides due to the spreading of salt or in the presence of marine atmospheres. Alongside these situations, the simple presence of carbon dioxide in the air alongside the pollutants usually present, contributes to causing damage to the reinforced concrete structures. The repair of the damage suffered is often extremely difficult and expensive and sometimes technically imperfect.
One of the most effective methods of protecting armor against corrosion consists in applying surface coatings. As for other steel structures, the protections used can be metallic and non-metallic. Non-metallic systems, such as those of the epoxy type, can have some disadvantages. The protective layer can be easily damaged during the phases of shipping, transport, folding and assembly of the cages, storage on site and pouring the concrete. In addition, the bond between the surface of the coating and the concrete is rather weak. Due to this lack of adhesion, these coatings have even been banned in some US states.
Among the metal coatings available, hot dip galvanizing offers the greatest advantages from both a technical and economic point of view. The coating obtained, as described, creates an inseparable union with steel that bears, within certain limits, even deformations without being damaged. We have discussed extensively in chapter 3 of the phenomena that cause corrosion of reinforced concrete structures and of the effectiveness of galvanizing protection.
Hot dip galvanizing for reinforced concrete structures has been widely tested in many countries, unfortunately some preconceptions about its use still persist in Italy. Indeed, even in critical conditions (delicate structures subjected to high corrosive levels) hot dip galvanizing has proven its worth. It has in fact been used in the construction of port facilities with excellent results. Studies and experiments carried out in different parts of the world in a coordinated manner between specific research centers, universities, sector operators and users have encouraged the use of this protective method.
In the event that the coating is damaged by bending with too narrow angles, cuts, welding or, in any case, there are uncovered areas, the zinc layer guarantees, as has been mentioned several times, a sacrificial protection. The cohesiveness of the bond between concrete and reinforcement remains preserved (indeed it is improved) and the risk of concrete flaking is greatly reduced, even with low excess thicknesses. In addition, the annoying reddish color typical of reinforced concrete with unprotected reinforcements is avoided, the sealing capacity is increased even in aggressive environments and any mixing errors are better tolerated.
It goes without saying that steel rods for reinforced concrete should be galvanized in accordance with the general regulations on hot-dip galvanizing (UNI EN ISO 1461), or according to the recent UNI 10622.
By correctly analyzing the costs and risks of unprotected reinforcements, it becomes clear that the additional expenditure allocated for galvanizing is certainly sustainable, since it is of the same amount as the cost of the steel (unmachined rod) that makes up the reinforcement. The amount is, therefore, modest compared to the total value of the building. In a certain sense, it can be considered as a very convenient insurance premium, payable in a single installment. When a balance is made between the costs and the consequences deriving from the damage caused by corrosion, in the context of an entire reinforced concrete construction, the investment required by galvanizing appears fully justified.
>Applications in agriculture
On farms, tools and technical equipment are predominantly made of steel: fences, nets, gates, atria, stable structures, farm buildings, tools, containers and so on. The old buildings made of masonry are, in fact, more and more often replaced by modern large steel structures that allow to use the available space in a more rational way.
In the field of intensive cultivation, galvanized steel greenhouses have been used for decades since they allow for buildings with large spans without the need for intermediate supports, whose internal spaces are fully exploitable for the use of cultivation equipment. Galvanized steel, in addition to meeting these needs, resists the corrosive conditions generated by humidity, temperature and chemicals, as well as the natural stresses of the external atmosphere. For the conservation of the products, the most suitable equipment were the steel silos, cylindrical and with a square section, since this material allows the creation of low weight structures, with high loading possibilities, at low costs.
Agricultural machinery requires the largest investments, but they are indispensable for carrying out agricultural activities. Typical examples are represented by tractors, trailers, fertilizer spreaders, mixers for liquids and solids, tools for working the soil, threshing machines, rainwater collectors and so on. Parts of these machines can be galvanized. Likewise on farms and stables there are automatic feed distributors, straw choppers, milking machines, etc. with a widespread use of galvanizing.
The substantially little polluted atmosphere of rural areas certainly generates reduced risks of corrosion. However, there are many solid, liquid and gaseous substances with high corrosivity. Inside the stables, for example, highly corrosive environments are created due to the presence of manure, urine and various residues, which are accompanied by high temperatures, humidity and ammonia fumes produced by the animal excrements themselves. Furthermore, mechanical removals may occur caused by the rubbing or trampling of animals, which however do not aggravate the problem of corrosion.
In addition, the equipment is frequently covered by dirt and deposits, which in the presence of humidity can increase the corrosive load, especially in areas that are difficult to access for cleaning operations. In such conditions it is clear that only the intervention of an adequate protection system can counteract the corrosive attack. It must be tough, durable, resistant to wear and, of course, economically advantageous. In the stables, in the event that protection by hot galvanizing is used, the most dangerous attack for the zinc layer concerns the areas close to the ground and, above all, the points where thresholds and jambs are inserted into the concrete of the flooring. . The high percentages of humidity and the consequent formation of condensation prevent the formation of the upper protective layer typical of galvanizing. A simple preventive measure consists in applying a layer of bituminous paint to the structures, for a height of 25 – 30cm from the ground, before drowning them in the poured concrete. Easy to implement, this system guarantees a long life to the galvanized structure.
>Services, roads and street furniture
A wide field of application is that of galvanized structures in services, in street furniture and on the roads.
The large operators of the transport and production of electricity, telephony and railway lines have for some time now almost immemorial have chosen galvanizing as the main option for the protection of structures in the atmosphere. In these important sectors, the quality controls of the creations are particularly strict, due to the importance of the function and safety requirements. Electricity companies have developed an in-house testing facility for protection systems with very stringent specifications and tests.
For these applications, there is no lack of evidence regarding the validity of hot dip galvanizing. With a study conducted in 2001 by the University of Ancona on low voltage pylons installed in the Ancona and Parma area for about 30 years, the researchers found residual thicknesses of the galvanizing layer still in line with the requirements of today’s tender specifications. . This means that the protection, even in terms of thickness, would still pass the testing tests today.
The network of roads and highways is also littered with galvanized material consisting of metal safety barriers, guardrails and new jersey, but also soundproofing fences, delimiting grids and lighting poles. While in the streets and squares of the city the use of galvanized steel involves not only all fences, poles and grids, but also bins and waste bins, equipment for gardens, kiosks, gates, road sign supports and everything else. which is made of steel and iron.
In the last period, we are witnessing the growth of an interesting market which consists of the protection of means of transport: galvanizing of chassis and bodies, parts of boats and railway wagons. Major car manufacturers, especially in France, have decided to take advantage of the properties of galvanizing, managing to ensure that the bodies are free from corrosion for long periods.
For these applications, the search for zinc alloys is being developed which will allow easier control of the growth and uniformity of the layer. In fact, especially for the components of the means of transport, the tolerances to be respected are much more stringent. Alloys with a high aluminum content (up to 5%) are currently being tested to allow the use of hot dip galvanizing even for coatings that cannot exceed the size of a few microns. In these cases, the high thicknesses which constitute the value of hot dip galvanizing for other applications cannot be accepted.