Nobody doubts the strength of steel as a construction material, but its qualities in the field of sustainability may be less immediately obvious, says Russell Ager from Crittall Windows
It’s steel’s strength that makes the key contribution to steel’s credentials as a sustainable, environmentally sound and cost-effective choice. Quite simply, it can be recycled or re-used without deterioration of its fundamental properties. This translates into high value over the product’s long life.
Steel components have been recovered for many years and the process for recycling is therefore highly developed. Current rates of recovery from demolition sites in Great Britain are 99% for structural steel and 94% for all types of steel construction. These percentages leave other types of building material in their wake.
Currently some 86% of the steel gathered as scrap is returned to the furnace while 13% is dismantled for direct re-use. This leaves just 1% that is lost to rust or landfill.
On a worldwide basis some 40% of all steel produced is based on the use of recycled scrap, that’s 500 million tonnes per year or the equivalent of 180 Eiffel Towers per day. For the UK market, that could be translated into 25 Forth Rail Bridges!
Of course, sustainability is more than just re-use and recycling – other important considerations include the environmental cost of manufacture. Produced using iron, the most abundant element on the planet, steel manufacturing’s impact is calculated by the World Steel Association using what is called the ‘system expansion’ method of life cycle assessment. This sees steel as part of a global system of supply and demand and takes account of co-products used in the manufacturing processes that save energy or reduce emissions. One example is waste gases being re-used to generate electricity for the process.
The full life calculation, which also takes account of steel’s high strength-to-weight ratio (meaning less achieves more) means that overall CO2 emissions associated with a steel building – from component manufacture through its life in use – will be lower than for other materials.
Beyond mathematics, the nature of steel and its construction also augments its sustainability tally. All of its fabrication, testing and certification takes place in a controlled and monitored factory environment. This approach means adherence to consistently high standards and quality, leading to safer and more predictable outcomes onsite. Construction processes can therefore be more efficient, not to mention more cost-effective.
A key element in the use of steel as a building material is galvanising providing protection against corrosion. In this process the steel is coated with zinc to prevent it from rusting. The cleaned steel is dipped into molten zinc at around 450°C and a series of zinc-iron alloy layers are built up by a metallurgical reaction between the iron and zinc, creating a strong bond between steel and the coating.
The galvanising process is energy efficient taken as part of a whole life cycle which is the only meaningful way of calculating the impact on such a long-lasting material. It prolongs the life of an already long-life product, and it does not affect recyclability or re-use. Galvanised steel can be thrown into the scrap furnace and steel can easily be re-galvanised. One particular building element that emphasises the sustainability plusses of steel material is the window frame. Manufactured under controlled conditions to reap the benefits already enumerated for steel as a material, Crittall Windows operates within the constraints of ISO 14001:2004; the international environmental management standard that sets targets for solids, liquids, gaseous emissions and waste generation.
But the finished product itself, which is galvanised for enhanced longevity, offers other benefits because of the nature of the material. Because of their inherent strength, steel windows have much thinner frames than is possible with other window materials. This lets in more daylight thus reducing the use of artificial lighting in the buildings in which they are installed. Taken over the elevations of a large commercial building this could lead to impressive savings in both energy usage and cost.
Supreme strength and matchless elegance are unusual partners, but they sit side by side in the world’s most recyclable building material. And who said sustainability and good looks could not go hand in hand?
Russell Ager is managing director of Crittall Windows