Embodied Carbon of Materials - PART 1

The materials of a site are the most important consideration when thinking about creating a carbon positive landscape. They are the ingredients in the recipe, the bridge between paper and reality and the physical product people interact with.

However..

The carbon cost of almost every site material a Landscape Architect has in their toolkit is almost never neutral, and is far higher than expected. This is due to a few factors - mining of resources/ metals, cement, manufacturing, processing, all likely the largest contributors to the embodied carbon of a material. Then include transport, delivery and maintenance into the mix and the figures keep ticking up.

‘Net Zero’

The push for the UK to be a net zero economy by 2050 means that the materials we procure and implement in schemes SHOULD be ‘net zero’ - so the embodied carbon of 1m2 of paving for example would be 0 (cradle to gate). In theory this will be possible to the renewable energy used instead of fossil fuels and any offset required to manage any excess carbon emitted.

In the production of cement however, CO2 is released as a byproduct of the process. So no renewable energy sources can change that. Added to that, it is a huge percentage of the overall C02 emitted. So to make cement use net zero, we need to:

1. Use less cement in the world (reduce demand / find alternatives)
2. Offset any excess.

Both of which are going to be difficult. However, we’ll explore current cement / concrete alternatives as part of this blog another day

For an easy visual reference:

Credit to

https://pliteq.com/news/building-vs-carbon-footprint/

https://www.materialepyramiden.dk

*NOTE figures vary depending on reference source. There are numerous figures and databases out there.

It can’t be a simple swap of materials to get a better carbon footprint unfortunately. Whilst gram for gram, glass beats steel, steel can be much more efficient at providing a balustrade for example, using less material.

Aggregate:

Is concrete paving or stone paving always necessary? I think the coming years will see a move to softer pathways and lower carbon thinking. Simplifying schemes will do this. Rural schemes (think National Trust ) already do this.

Using aggregate which would go in as the base to paving anyway as the finished material could save a lot of carbon. Approx 5kg carbon per tonne of material. Massively varying depending on source.

Rammed Earth

What is the potential of using rammed earth for low use pathways? Or even retaining walls? We will explore this further in another post as there may be huge potential.

Reused materials

There is virtually no carbon footprint associated with reusing materials on site. Only diesel and energy used on site (still important to reduce..)

Repurpose and reimagine what all of the site elements can do.

Timber

There is a lot of talk within the construction industry around utilising timber for buildings instead of concrete and steel. Timber has been used since time immemorial but not to build skyscrapers. It is warm, natural and importantly - sequesters carbon.

For landscapes, timber can be used in furniture, decking, signage, structures, edging, fencing, and many other applications. It is a beautiful material to work with and products some stunning results. However it’s often seen as the cheap, low cost and high maintenance option which needs to be replaced regularly. As such the ‘off the shelf’ options are often domestic in their aesthetic and not desirable in a public space. Or they are extremely bespoke and therefore cost a lot of money. Maybe the money saved in efficiencies of reusing materials and a creating a low resource landscape could be re-spent on beautiful bespoke timber pieces?

Tactile paving and associated infrastructure for accessibility.

The drive to improve public spaces to provide greater accessibility is a great and highly valuable endeavour, directed by building regulations, and BS8300 among other guidance. However, they are onerous and specific in the application of meeting certain requirements. I.E the use of concrete tactile paving in surfacing for crossings or hazard warning.

How can we reimagine this?:

• Maybe using metal studs embedded in existing site materials?
• Or sawing ridges into existing materials on site?
• If new concrete paving is to be used - use the best EPD rated version around.
• ASK for the EPD certificates from the suppliers. This will prompt them all to become more conscious of their processes.

Lighting

Not sure about this one - Let us come back to this. If steel can be Net zero then we have wires, glass and plastic tubing to worry about.

Paint markings and Signage

Timber signage could work for most applications (with a steel base inserted into the ground). Maybe hempcrete as the concrete substitute base

Having recently visited the David Mellor museum in the Peak District, I enjoyed the simple understated use of green markers to define the parking bays. Maybe this approach could be used in more spaces to demarcate a space (cars or otherwise), and reduce the amount of thermoplastics in the ground.

Foundations

As an alternative to concrete and rebar - can stone be used as foundations? It has a fraction of the embodied carbon and much of the same properties. Plus has been used to build buildings before the invention of concrete..

Let us know what schemes you have seen which employ these techniques already!

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