Reusing concrete and steel in the construction sector

Prof Dennis Lam from the Faculty of Engineering & Informatics at the University of Bradford describes research reusing steel beams and concrete floor slabs to save energy, avoid waste and reduce carbon emissions. 

How large are CO2 emissions from concrete and steel? 

Worldwide, the steel industry accounts for approximately 5% of global CO2 emissions. On average, 1.9 tonnes of CO2 are emitted for every tonne of steel produced. According to the International Energy Agency, 2.8Mt CO2 per year are solely related to energy use in the steel sector, about 8% of total energy-related emissions. Concrete is the most widely used man-made material in existence. But, while cement - the key ingredient in concrete - has shaped much of our built environment, it also has a massive carbon footprint. Each year, more than 4 billion tonnes of cement are produced, accounting for around 8 per cent of global CO2 emissions.  

Why is it important for the construction industry to move to a circular economy? 

The construction industry in Europe currently consumes over 70,000 million tonnes of materials each year and generates over 250 million tonnes of waste. There is growing recognition that current consumption patterns are unsustainable and a move from linear to circular economy is urgently needed.  Circular economy is an economic business system aimed at minimising waste and making the most of the current resources. This regenerative approach contrasts with the traditional linear economy used by the construction industry. Developing new construction technologies for a resilient society is a top priority for the construction industry throughout the world.  

What negative climate impacts arise from concrete and steel flooring in multi-storey buildings? 

Much of the environmental impact from the construction industry is associated with the consumption of resources and energy, as well as carbon emission and waste. In multi-storey building construction, composite flooring formed by connecting the concrete slabs to the supporting steel beams has been widely used for many years and is well established as one of the most efficient flooring systems.  Although steel construction already has good circular credentials through recycling, this process is energy demanding, while concrete can only be downcycled or reused as recycled aggregates, flooring contributes to a large volume of concrete being used in multi-storey buildings.  If both steel and concrete components can be reused without remanufacturing at the end of life of the structure, this could save significant resources and reduces carbon emissions, and moves up the waste hierarchy from recycling to reuse.  

What did the project aim to do? 

The project explored the design for deconstruction and reuse in commercial and residential buildings using steel-based structural systems, which addressed the conceptual design of demountable, composite structural systems for beams and flooring system. This leads to the use of demountable shear connector systems (see header image) which were investigated in this research. A new composite flooring system that allows for the reuse of the steel beams and composite floor slabs were developed and tested at the University of Bradford to assess its potential and suitability for reuse.  

How did this work show a reduction in carbon emissions could be achieved? 

The result showed that similar load resistances were obtained from the first-use composite beam and the composite beam with reused steel beam and composite slab segments. Testing of the demountability and re-assemblability also showed that the flooring system can be easily reused without additional erection tolerances. Quantification of the benefits of demountable building and reusable steel structures were also made using existing whole life cycle assessment methodologies.  In building construction, because the volume of concrete used for flooring is much higher than the steel counterpart, therefore, if we could reuse both the steel sections and the concrete slabs, it would have huge benefit to the climate change.