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In 2018, the British Precast Drainage Association (BPDA) sought the services of Circular Ecology, the consultancy behind the ICE carbon footprinting database, to help them quantify the true whole-life carbon emissions associated with concrete and plastic pipeline systems. What Circular Ecology came up with (see report here) did not only help BPDA plans to improve their concrete pipeline products; it also revealed a wide range of hidden factors that can significantly change how the industry perceives embodied carbon and generic products’ carbon footprints.

How generic carbon footprints are used

The last five years saw a significant increase in the number of carbon calculators developed by Water Companies and asset operators to help them assess and manage carbon emissions from their infrastructure projects. Asset operators generally prefer to use generic values to assess the embodied carbon of different construction products. By multiplying the quantities of construction products (tonnage, m 3 , etc) within bills of quantity by the generic carbon footprint values, it is possible to come up with a very quick estimate of the embodied carbon emissions of entire projects. This is why such generic carbon footprints are highly valued by the industry. For the last 15 years, the most used and trusted source for generic carbon footprints in the UK has been the ICE Database (known previously as the Bath University database).

But questions remain on whether such generic footprint values are always reliable and sufficient. The model developed for us by Circular Ecology, and the subsequent work we did to make up for a few missing pieces within that model, was specifically to help answer this question. More information on that study can be found here.

Circular Ecology’s assessment/ Model

The British concrete pipe sector has long claimed that concrete pipes have a significantly lower carbon footprint compared to HDPE alternatives. We published two studies in 2002 and 2010 to prove this. However, due to lack of any certified carbon footprints for UK- produced HDPE pipes, such comparisons have always been difficult. The only publicly available carbon footprint for HDPE pipes was published by Plastics Europe almost 15 years ago. It was updated only once in the last few years. That carbon footprint is based on European plastic resin and extrusion factors, using a methodology which is not fully compliant yet to the main footprinting standard, EN 15804. We asked authors of the ICE Database, Circular Ecology, to come up with a new HDPE pipe footprint which can enable comparisons in accordance with EN 15804. Circular Ecology was also asked to oversee the comparison to ensure that the main functional equivalence elements are accounted for.

Circular Ecology came up with a multi-scenario model to enable a viable whole-life comparison between concrete and plastic pipeline systems. The model accounted for different options for GWP factors, sources of HDPE resin, steam cracker allocation methods, raw material shipping scenarios, “Design Life” and a number of other elements. Circular Ecology left out some elements where they felt sufficient data may not be available to enable a viable comparison. Extra work not covered by the original contract (such as extra work to account for realistic factory waste or road transport) was also not added.

BPDA made a couple of corrections to account for realistic factory waste and transport (factory to site) impacts for both concrete and plastic pipes. In both cases we used published industry figures. BPDA also sought help from Professor Göran Finnveden, an academic from the KTH Royal Institute of Technology in Sweden, to help build up the End-of-Life impacts of HDPE pipes, which were missing from the Circular Ecology model. Prof. Finnveden worked on GHG emissions associated with the degradation of plastics in the past and he suggested a CO 2 / CH 4 degradation factor which we can use for buried HDPE within its first 100 years of installation, running into post End-of-Life. We used the most conservative degradation factor (within 100 years only) to ensure that such GHG emissions are not over-estimated.

So, what did the study unearth?

Where to start? Based on the most-realistic scenario we developed using the Circular Ecology’s model, and Prof Finnveden’s E-o-L factors, we found the following:

  • The choice of characterisation factors for Global Warming Potential (GWP) can make a noticeable difference. Using a methane GWP which accounts for carbon feedbacks (as recommended by latest standards such as EN 15804 +A2 and ISO 14067) can lead to a 2% increase in the resin’s embodied carbon.
  • Aligning the allocation method within steam cracker production (the process which produces raw material ethylene) to EN 15804 rules roughly adds an extra 7-8% uplift to the carbon footprint of HDPE resin.
  • The source of HDPE resin can make a significant difference. An HDPE pipe manufactured from Middle Eastern HDPE resin can have a carbon footprint 33% higher than one made of resin imported from a European country like Norway.
  • Including pipes’ bedding in the carbon assessment can add up to 33% to the carbon footprint of an installed concrete pipe compared to 72% for the carbon footprint of an HDPE pipe.
  • The End-of-Life carbon emissions of HDPE pipes are so significant, it can increase the final carbon footprint by around 14-17%.
  • Accounting for Whole-life as recommended in EN 15978, where the Design Life of pipes are primarily considered, will lead to a 100% increase in HDPE pipes’ embodied carbon emissions as pipe replacement would be needed to cover a service life of 120 years.
  • There could be further environmental impacts (including GWP emissions) from the use of plastic pipes. Plastic pipes degradation beyond the service life (over 100s or 1000s of years) was not accounted for. This is despite the availability of viable figures from the KTH Institute research. We also decided not to include carbon emissions associated with pre-production HDPE resin pellets finding their way into the ocean, as we couldn’t find a reliable way to estimate such impacts.

Over the next few weeks, we will be publishing a number of detailed blogs demonstrating the significance of each of these findings.

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