We believe that the mast is the most important design element along the road. Others may see masts as a necessary evil to position lighting fixtures, signal heads, or signage at the correct height above ground.
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Disclaimer: The following text, including any references to products and case studies, is based solely on Danish laws, regulations, and standards. Interpretations and applications may differ in other countries.
Written by: Emil Mortensen, Head of the Mast Department at DAV NORDIC A/S
We believe that the mast is the most important design element along the road. Others may see masts as a necessary evil to position lighting fixtures, signal heads, or signage at the correct height above ground. Regardless of perspective, masts are a permanent part of the Danish roads.
In recent years, many older installations using wooden or lattice masts have been replaced. The new masts being installed are primarily made of steel or aluminium, usually surface-treated by galvanisation (steel) or anodisation (aluminium).
Steel is extracted from iron ore through a process in which it is heated to approximately 1,700 degrees Celsius to remove oxygen from the ore. After production, steel is typically galvanised in a bath of molten zinc at 375 degrees.
Aluminium is extracted from bauxite through electrolysis and heated to approximately 650 degrees. Once produced, aluminium can be anodised to extend its lifespan. The anodising process is electrolytic and takes place in an acidic bath between 30–50 degrees. Anodisation strengthens the natural oxide layer of aluminium and changes the appearance of the material. Various colours and finishes can be selected during anodisation. In the photo, the left side shows a natural anodised surface, while the right shows a raw brushed finish. Natural anodising is the most commonly used finish for masts.
Exact figures for the CO2 footprint of the two processes are difficult to specify, as it depends on several factors – such as the energy source, alloy composition, and production methods.
It is generally estimated that 1 kg of steel emits about 1 kg of CO2, while 1 kg of aluminium emits about 2 kg of CO2. However, aluminium weighs only about one-third of steel. Since aluminium often requires greater wall thickness due to its material properties, the total emissions for producing a steel mast and an aluminium mast are roughly comparable. The real difference lies in recyclability and the energy required for surface treatment.
Circular economy is here to stay. Increased political focus is expected to drive demand for recyclable solutions.
In this context, the concept of “cradle to cradle” is often used to describe the full lifecycle from production to use and reuse. In the past, the model was “cradle to grave”, without consideration for recycling. The idea behind the circular economy is to reuse resources and minimise waste and emissions.
Both steel and aluminium can be recycled. Recycling aluminium requires only 5% of the energy needed for primary production, whereas steel recycling requires around 25%. This significant difference means that about 75% of all aluminium ever produced is still in use today.
Aluminium emerged about 50–60 years ago and has grown steadily since. The industry has adapted to evolving technologies. Recycling has been an important focus throughout. Today, recycled aluminium is a standard product and can easily be specified for mast procurement. The cost of recycled aluminium is not significantly higher than that of virgin material, which is why many manufacturers use it as their standard.
Steel has been around longer but has not made it as easy to verify whether recycled materials are used. It is therefore more difficult to source standard products made from recycled steel. At present, recycled steel is a more challenging requirement to fulfil.
To protect masts from corrosion, they are typically surface-treated. Steel is galvanised, and aluminium is anodised.
Steel is manufactured in various strength classes, with S235 and S355 being the most common. Aluminium is available in many different alloys, each with varying corrosion resistance.
Some aluminium alloys are designed to last over 50 years in coastal environments, while others are intended for indoor use. Alloys must therefore be carefully selected according to the application. The main selection parameters are corrosion resistance, strength, and cost. Additionally, it must be verified whether the chosen alloy is suitable for anodisation, as not all alloys can be anodised. Many aluminium alloys do not require anodisation to meet expected durability in their intended environments.
Most masts are made from aluminium in the 6000 series, which is also widely used in the construction industry. Several alloys in this series have a documented lifespan of at least 25 years without anodisation. Nonetheless, most masts in Denmark are anodised to add extra corrosion protection.
The most critical corrosion area for both steel and aluminium masts is at ground level. In such areas, aluminium is often treated with tape, plastic, bitumen or similar materials to strengthen its corrosion resistance, especially in harsh environments.
A Swedish report has previously highlighted issues with aluminium corrosion at ground level where road salt is used. The report was produced following incidents where masts in Sweden collapsed due to corrosion. However, the tested masts were made from a different alloy than those typically used in Denmark (AW6060, AW6063, and AW6005) and had not been treated at ground level.
Did you know that… The Danish Technological Institute states that by the year 2050, we will need 3.5 Earths if we continue consuming resources for construction and civil works at the current pace. It is therefore necessary to incorporate sustainability into the construction industry.
The Danish Technological Institute states that by the year 2050, we will need 3.5 Earths if we continue consuming resources for construction and civil works at the current pace. It is therefore necessary to incorporate sustainability into the construction industry.
The first aluminium lighting columns appeared in Denmark around the year 2000, when the Danish Road Directorate introduced the MILEWIDE column. For many years, the columns were anodised but left untreated at ground level. These columns can be seen in many places across Denmark, and several have now been standing for almost 20 years. So far, there have been no issues with corrosion on these columns made from the AW6005A alloy. With the correct choice of alloy, we argue that no additional corrosion protection at ground level is necessary. Ground-level corrosion protection can be considered an extra insurance.
There are various sources that provide information on the corrosion resistance of specific alloys in different environments.
Read more about how columns are classified in terms of corrosion resistance here.
As demand for aluminium masts has increased, the price has approached that of steel masts. The price of aluminium masts has decreased in recent years and is now closer to steel when comparing similar volumes. For a typical 4–6 meter embedment mast, the price is approximately 30–35% higher for aluminium than for steel, depending on quantity. The price of aluminium masts is not expected to fall further, as production processes have already been significantly optimised.
Both steel and aluminium masts can be designed to be energy-absorbing. However, the natural material properties of aluminium make it especially well-suited for yielding behaviour. Steel, being stronger, often requires special design features to reduce stiffness and avoid whiplash effects.
Most aluminium masts, when constructed as standard lighting columns without specific yielding design, will still perform as yielding in crash tests. A yielding aluminium mast is therefore often a standard mast. Several are even certified as yielding when embedded directly in the ground (without a foundation).
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