End of life carbon and beyond – transitioning to a circular economy

Transitioning the construction sector to a circular economy is not just about reducing emissions today but ensuring our buildings and materials are part of an ongoing cycle that benefits future generations. 

Many of the discussions about carbon and indeed carbon calculation focus on modules A – C life cycle assessment processes. In fact, there is often a lack of robust data about end of life and beyond carbon impacts, which limits meaningful assessment of impacts (or benefits) in these stages of construction. 

We obviously have a need to decarbonise our built environment now in order to meet our national carbon reduction targets and address the challenges of the climate crisis. MBIE’s Building for Climate Change initiatives are a step in the right direction and rightfully focus on whole of life emissions. If we don’t start to think more about circularity of our buildings and their component systems and materials, we risk solving our immediate problem and then deferirng the problem for the next generations to deal with when our building stock being built now comes to the end of its life.  

We need to solve both problems – i.e. how do we get carbon out of the buildings we are constructing now and how do we ensure that we are not then deferring the problem to the end of their life. This is where circular design as a component of Construction 4.0, becomes important. That is, how do we design for reduced end of life carbon too?  

To do this, we need to stop thinking about the lifecycle of a building and think of the lifecycles of a building and its materials – this is circular economy thinking. It takes modules A-D from a linear end-to-end process and converts it into a cog wheel that continually cycles materials through the supply chain. Transitioning the construction sector to a circular economy is like rethinking how we handle our personal belongings: instead of buying and discarding, imagine a wardrobe where every piece of clothing is designed to be easily repaired, reused, or recycled into something new, ensuring nothing ever truly goes to waste.

What do we need to make a circular economy for building materials?

Steel is already a rockstar of Aotearoa New Zealand’s circular economy. In fact, in the HERA Steel Recycling Report undertaken by thinkstep.anz, it was found 85% of our construction steel is already being recycled, providing a net benefit of about 793,000 tonnes of CO2 equivalent each year.  

However, if we look at the hierarchy of waste reduction in the below diagram, recycling is pretty low. We need to get to reduce (which clever design can deliver, and HERA is working on achieving too!) and re-use. 

Material passports are key to creating an effective circular economy

In order to re-use a material, we need to have reliable and transparent data about its fitness for re-use. This is why a material passport is required. A material passport provides a digital inventory of all the materials used in an object (e.g. a building, a structural system or element), along with any data that is important to enable use in a circular economy.  

For steel, the likely considerations required of a material passport are shown below.  A material passport does not currently exist, but HERA is in the process of developing one for steel.  

What does the future look like with material passports?

At HERA, we are re-imaging buildings as banks of materials. The materials that have been used in the building then become available for “withdrawal” at a future point in time.  

This means that: 

• design for re-use will become important – we will need to change the way we design. For example, it may mean less welding and more bolting to make disassembly simpler; 
• building health monitoring will provide valuable data – we will require more data about the events that a building is exposed to, such as earthquakes; and 
• business models will become circular. Wow! The options here are endless but the potential for business model innovation is clear. For example, would fabricators lease out their columns or would they buy them back at end of life and re-purpose them?

How does a material passport and circular design link to Construction 4.0?

It is easy to see how Construction 4.0 technologies will assist the development of material passports. Key enabling technologies, which are all within the wheelhouse of Construction 4.0, would include: 

• AI; 
• digital twins; 
• scanning; 
• blockchain; 
• Construction 4.0; 
• AR; 
• machine learning; 
• BIM; 
• optimisation of circular design; and 
• NDT (these will need to be developed and dealt with in the regulations to faciliate versus hinder re-use). 

A case study: adaptive re-use that could have benefited from a material passport

Auckland’s CAB building is an example of adaptive re-use, whereby retaining its 18-storey structural steel frame saved 6,150 tonnes of carbon.  

When the building was constructed, the details of the steel used would have been documented and known (i.e. “identified”) but through the passage of time, the mechanical and chemical properties would have been lost, leading to an “unidentified status”. This would have required extensive investigation to ensure fitness for retention, estimated to have cost in the vicinity of $60k direct costs and three months delay. Having a steel material passport in play (and the regulatory system in place to work with it) would have greatly assisted.