Notice: This blog piece was created prior to the formation of the British Precast Drainage Association.

Posted by & filed under Sustainability.

Will there ever be an end to the relentless series of claims by product manufacturers that their product has superior carbon footprint credentials compared with competitors’, only to be followed by those same competitors claiming superiority based on yet another set of studies?

And how do specifiers decide who to believe?

By way of an example, the concrete pipeline industry is fighting its own battle with plastic. In 2010 CPSA published a detailed report based on the most comprehensive study of its type ever undertaken, providing embodied carbon footprints for precast concrete pipes, manhole rings and cover slabs. This study was then used to produce two further reports providing carbon footprint comparisons between concrete pipes and plastic pipes and between alternative manhole construction methods.

The pipe comparison study indicates that concrete pipes have up to 35% lower cradle-to-site embodied carbon when compared with HDPE pipe using the same full granular (Class S) bedding design. However, rigid concrete pipes can often be used with alternative bedding designs using less imported granular material, whereas standard stiffness plastic pipes will invariably require Class S. The result of which is that the potential carbon (and installed cost) saving with concrete pipes can be even higher.

After several years silence, the plastic pipe industry responded. Using the embodied carbon values for concrete pipes from the CPSA study, an alternative set of values were presented for plastic pipes. These values were based on a much older “generic” study using Bath University’s Inventory of Carbon and Energy, taking an average across a wide spectrum of products and geographical sources; unlike the CPSA study for precast concrete pipes, there was no new study based specifically on the manufacturer’s own plastic pipe products. And the comparison did not include impacts for alternative bedding designs.

Using this generic data, the results of the study indicated a lower carbon footprint for plastic pipes.

But is this riposte valid? Is it right to use data specific to a single product type (CPSA concrete pipe study) and compare it with generic data across a wide spectrum that does not represent the manufacturer’s own product? Different accounting methods will lead to different results. Does it make sense to make a comparison where the results were derived by separate methodologies with different rules and boundary conditions?

Almost all UK carbon databases and calculators use data for plastic pipes that trail back to data for resins from a study in 2005 by TNO for Plastics Europe. Recently, the integrity of this data has been questioned as the allocations to distillate products used in the Plastics Europe study do not appear to comply with the rules set out in the construction industry’s most recognised methodology, EN 15804. The Plastics Europe study assumes that the plastic pipe manufacturer is located 100km from the source of the resin. For a UK plastic pipe manufacturer, this is extremely unlikely. Resin supplied from further afield, such as the Middle East and Asia will significantly increase the carbon footprint of plastic pipes manufactured in the UK due to higher emissions from grid electricity plus emissions associated with transport.

Be aware. The plastic pipe industry has not embraced EN15804, the main Standard for carbon accounting in Europe for construction products. Instead, they have elected to follow an alternative route via Product Environmental Footprints (PEFs). Maybe the numbers work out more favourable for plastic using PEF rather than EN15804?

Concrete pipes Vs Plastic Pipes. Which has the lower carbon footprint? Whose claims do you believe?

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