The project I’m about to show you started from this question.A literature review of only Cradle to Site studies of buildings throws up huge variation. Yet we are being sold simple absolute answersSteel is better than concrete as its recyclableConcrete is better than steel as it has thermal massTimber is renewableEmbodied impacts are smaller than operational impacts so why are we considering it?We have a big database in arup containing a number of hundred published embodied energy and co2 studies and we felt that we should be able to extract some benchmarks from these studies for our design. But to do that we need to understand how to deal with the variation.
For me -its all about responsibility. I don’t believe there is one big answer to solve climate change. It is a collective effort. What is interesting about sustainability for me as an engineer is that it is all about how we make things. We know that some of the materials we specify exhibit a genuine variation in embodied co2. This piece of work shows how the impact of concrete varies with strength and composition. We wanted to investigate this.AN EXAMPLE is PT CONCRETE – We had noticed that the ECO2 of PT mixes on our projects was consistently high. So we embarked on a project with Arup/ExpandedLtd/Stanhope plc which has just won the CONSTRUCT 2010 Award for Innovation and its Adoption at Chiswick Park which involved a 30% reduction in embedded carbon levels in post tensioned concrete. We need to be aware of how our materials vary and for PT we need to make sure that the material saved more than offsets for the higher impact of the raw material. We also know that there are lots of different impact values published for our structural materials. Its confusing ! - Different boundaries for studies of embodied impacts can throw up really different results. We wanted to investigate that too.We are very thankful that the Concrete Centre provided us with a fantastic dataset with 20 buildings typical of UK construction designed to only 3 different specifications. This has allowed us to do a detailed piece of work looking in depth at one piece of the jigsaw. (Summer - 380 total cementitious with 28% of pfa )
Using the cost models that Jenny has shown you we were able to create a large data set of embodied carbon values for typical UK buildings. With each of the 20 solutions we can create 5 variants. -Typical-Upper and lower bound of impacts that we can control through specification-Upper and lower bound of results that would be generated with different methodologies. These were based on different values used in studies in the public domain that used the same time boundaries. An example of a different methodology for concrete would be to use a particular process (such as a wet kiln for cement) rather than the average process mix for the UK. An example for steel would be to report only on a particular production process for steel (BOF or EAF) or to use a higher recycling index. We have used the average world recycled content across all products for our typical values for steel. We completely agree with the advice from eth steel industry that specifying recycled content of steel for a project can be counter-productive to the efficiency of the supply chain.This is the summary of some of the results. We have since added this to our large database of published papers and our own projects in order to be able to extract benchmarks which are relevant to particular projects. The results fit fairly consistently with other findings. We find that splitting out structural scheme is much more informative than looking at material choice. This graph shows…You may think it tells you that there is not much difference between schemes. Well this is the average of many examples. When we do calculations on projects we usually find more variation between schemes. We can use this to set benchmarks for structures. We can use it watch out for situations when we may be comparing upper bound of one solution with the lower bound of another. We can use this to see the potential for reduction in impacts
This graph shows the whole building impact for a collection of different schemes and structural specifications of the office example. The grey bars are the non-structural impacts. The yellow ones are the structure. The changes in the grey bars are only due to changes in the structure – eg floor to ceiling height saving façade etc. This shows that the knock on effect of the structure is pretty small. It is worth investigating all possible savings in the structural frame impacts and it Is likely that the effect on other impacts will be small. The same can be said of the operational impacts. MOST of the schemes could include exposed thermal mass. So we feel en-boldened to take the eco2 of structure seriously & look to reduce impacts where we can through specification and optimisation of design.
Because we were a bit shocked by the variation in our literature search we investigated the variation in impacts.If I were a client who commissioned co2 footprints of projects from different consultants I would take some care about comparing them. If we are comparing two different studies and the difference between structural impacts Is less than 30kgco2/m2 we don’t think this is necessarily a significant difference. Although the guidance and standardisation around EC02 calculation will improve we feel that there are circumstances where for each project decision a different boundary may be appropriate. What is important is to use a consistent measure when comparing schemes & to investigate sensitivity around key decisions. We need standardisation in approach but we also need to allow for innovation.
As structural engineers we are used to being told that we have no contribution to make –to co2 reduction, to breeam etc. But – the difference between the best decision and the worst decision of design and specification was ~1000tonnes of co2. Making the best decision did not negatively impact on other disciplines.The window of opportunity to mitigate climate change is NOW not in 60 years. So this is something that we should be doing.400 journeys from London to 500 return flights from London 80 years of goods and Manufacture / useJohn O’Groats for a 20t truck to Hong Kong for one person services for a UK citizen of 20,000 iPhones Equivalent value of 1000 tCO2
Cost Model Studies & Embodied CO2 Study
Cost Model Studies&Embodied CO2 Study<br />Jenny Burridge<br />The Concrete Centre<br />