Burgess COMMENTARY

Peter Burgess

What's more sustainable: Concrete or steel? And can life cycle assessment help you to make an informed decision? Daniella Abreu takes a deeper look. Concrete How many times have you seen people trying to argue that either concrete or steel are better materials, less carbon intense or ‘greener’? Yes, many. And yet there's rarely a clear, definitive answer. The problem is there is no clear definitive answer to this question. So, what are the environmental, capital cost and lifetime cost of these two materials? As with everything related to sustainability, the answer is: 'It depends'. It will depend on where the steel or concrete comes from? What is the percentage of raw and recycled content? What source of energy is used during manufacturing? What is the transport used during the entire process? Where is the building or structure going to be located? And so on. So how can you possibly make a sustainable decision between the two materials? LCA is not as complex as it sounds and can help you to understand a lot more about your project Well, I believe that life cycle assessment (LCA) can really help you on this. But before diving into a full LCA calculation there are other things you will need to consider. 1. Have you got an option? Firstly, check if there is any flexibility on the design? If the client wants a steel tower and is not open to negotiation, there is no point trying to calculate anything. (Although I would do the calculation and try to convince the client anyway.) 2. What is the building operational consumption? Okay, so there is flexibility. Let’s check the obvious implications on the operation of the structure. Operational impacts will almost always be more important than construction impacts, so look at these first. If you can easily see that the operational impacts of the two structures are very different, you don’t need to go further. For example, the building might be a school in a hot climate and the concrete frame will obviously help to reduce the need for air conditioning in the next 20 years. However, if you are not sure yet, if it is not so obvious, if you can somehow make the operational consumption similar for both structures - you will need do some more calculations. 3. Carbon footprint for construction Calculating carbon footprints is a simplified way to consider the impact of your materials, as it only gives you some of the environmental impact and not the full sustainability assessment. Today, most of the larger suppliers are able to give you the local carbon footprint of their products. Ask for the local calculation - and not the ‘equivalent calculated in Denmark’. Different countries have different energy mixes and this changes the carbon footprint a lot. With this at hand you can compare the two carbon footprints and see if the differences are significant. Do the calculations only for the ‘bulk of the materials’, and don’t bother with all the smaller quantities. Go for foundations, structure & cladding. But remember: The carbon footprint is just one component of sustainability. It is an important environmental one, so if you do have the carbon footprint details you can (probably) make a more environmentally-friendly decision. However, if you really want to make a more sustainable decision you need to keep digging. 4. Life cycle analysis So, now you are really interested in knowing more about the impacts of your materials. In this case you will need some professional help and you will need to find someone that can help you to calculate the whole LCA of your building or project. This is not as complex as it sounds and can help you to understand a lot more about your project (possibly making considerable changes to the way you design, procure and manage a project). 5. So, what's next? If I have interested you this far - and perhaps convinced you that LCA is a good idea - you probably have a lot more questions. What kind of information can LCA give you? How does it work? Where can you find some help on this? I’ll not attempt to answer all of these questions here, but let me point you to some very useful links: Wikipedia Inventory analysis of LCA on steel- and concrete-construction office buildings Future use of life-cycle assessment in civil engineering Gabi software by PE International Simapro LCA software And check out these two videos on the subject: I hope this post made you think differently about concrete and steel (and other materials). Use the comment boxes below if you'd like to get in touch, make a comment or ask a question. And don't forget to follow me on Twitter @Dr_Sustainable.