In PART 1 we explored the highest emitters and the biggest challenges (hint: cement..), along with some alternatives to start thinking about. This section will further explore low carbon alternatives to start employing now, and how we can begin convincing clients and contractors to a new way of thinking.
Reminder of Key Terms:
Whole life carbon - the C02 equivalent of greenhouse gases (carbon footprint) emitted during the whole life of a material, or combination of materials. From raw material extraction, processing, transport and end of life (recycling / demolition / waste).
The aim is to have the amount of C02 associated with a material as low as possible so we reduce emissions in the atmosphere.
STONE
As stone is a natural product, the carbon footprint comes solely from the extraction (quarries), processing (cutting / shaping) and transport.
It is too easy these days to specify a specific product from a big stone supplier, not be aware of the location, and easily rack up a huge carbon bill due to the shipping costs of many tonnes of stone. But you can see why this happens -stone in the UK is expensive!
👉 A starting point would be to source reclaimed stone (from the site or nearby).
Next would be to then use UK quarries, and balance the financial cost by using less and thinking carefully about exactly why and where it is needed.
👉 European stone can be also an option and also from further afield, but again - think carefully about why this is needed and does it bring a net benefit to society? Modern Slavery checks should also be undertaken by suppliers to ensure their quarries are adhering to adequate human rights.
Example footprints:
Stone sourced in the UK (Aberdeen, and shipped to London) would have a footprint of 107kgc02 per tonne. 1m2 at 60mm thick granite this equates to 17kgc02/m2 (https://www.sciencedirect.com/science/article/abs/pii/S0921344911001406#:~:text=From a survey of eight,to the impact of transport.)
Chinese granite would have 96kgc02 per m2. (Marshalls, Callisto granite)
How does this stack up to concrete paving?
Tobermore concrete paving 50mm thick = 32C02eq./ m2 https://www.tobermore.co.uk/professional/products/paving-flags/braemar-flags/
Marshalls concrete paving 50mm thick = 20kg C02 / m2 https://www.marshalls.co.uk/commercial/product/conservation-x-paving
It’s clear there is a huge impact from stone from abroad.
LOW CARBON CONCRETES / ALTERNATIVE FOUNDATIONS
As a landscape architect, I am forever specifying materials and furniture which require a structural foundation. The standard approach is to annotate these elements ‘to engineer’s specification’. This is correct in that we are not structural experts, however we then lose control over what that solution is. With a little more guidance we can impose a lower carbon alternative for the engineer to review.
Collaborating and communicating with co-consultants os necessary to being able to do this well.
- Less cement content - a post foundation doesn’t need the same cement content as the foundations for a building.
- Hempcrete alternatives - Hempcrete blocks can be used in low-structure situations. Potential use for landscapes could be as blockwork for low walls, clad in lime render and site won stone.
- A certified low-carbon concrete which uses waste slag material instead of cement Can reduce up to 780kg of embodied carbon in 1 tonne of concrete. This is unlikely to be a useful long term solution as the waste is from energy intensive steel processes which are ever improving.
- Cement / Binder alternatives - alternatives to waste slags that replace cement as a binder
- Stone (see above section)
- Concrete foundation to engineer’s design. Low-cement concrete to be used and minimum size for stability to be adhered to.
- Hempcrete foundation to engineer’s specification
- Foundation to engineer’s specification to meet embodied carbon requirement of x CO2 eq. Per m3.
Furthermore, products like metal screw piles could be used to create foundations for larger elements if necessary. SEE - (LINK)
RECYCLED MATERIALS
Site won materials are the easiest way to save excess carbon use on a site. The majority of current practices unfortunately take a blanket sweep approach and clear the site to replace old with new. In many cases, the old isn’t actually that old and with a little TLC can be reused or repurposed.
This will involve a shift in skills and procurement processes for contractors. We need to simplify the process of quantifying, specifying, refurbishing and reusing this site material. That will be a big ask for clients and contractors.
Other techniques like crushing site concrete for hardcore can also be carbon beneficial.
The current model for new materials goes something like this:
Design > quantify drawings > price drawings > buy material > manufacture > deliver > install
This needs to look something like:
Quantify site material > review how much can be reused > design > confirm process with contractor > price > install
Add in a couple of steps around site clearance / storage / processing material etc then there is roughly the same number of steps, but inevitably a little more time in carefully understanding what can and can’t be reused. Ensuring contractor buy-in is also necessary so the process is understood and material not wasted.
The cost of storage / refurbishment and relaying will be higher than buying new. However there is no material cost, so this should balance out. Then there is the consideration of liability for failure. This onus would need to land on the designer / the contractor or specialists who have advised on the reuse, instead of say the manufacturer of new paving.
The skills to revitalise stone and metalwork may not be as freely available as the skills to lay new paving, so clients will need to understand this and see the balance of money will shift as we move away from buying so much new stuff.
SPECIFICATION
Similar to above the current specification and procurement process in creating a new landscape is smooth. We design a site, pick a material, write a clause in an NBS and your QS is happy as Larry.
There could also be a lot more specification of salvaged materials from reclamation yards (i.e the Reclaimed Brick Company in Sheffield). However, the guarantee of having the exact material in the required quantity less reliable than going through a big stone supplier. Long term jobs need long term commitment to price and contractual obligations.
Specification clauses need to be less focussed on installing new materials and refocussed on to the standards of workmanship, repair, and reinstatement that are required for site recycle materials. Including:
- Removal from site or it’s current location (if necessary)
- Storage (ensuring it is safe, adequately stored and not prone to damage or vandalism) - This will be a big convincing factor, particularly on smaller sites where on site storage is difficult.
- Repair
- Reinstalling back on the site - ensuring modern techniques don’t damage them long term - i.e using a lime based cement with reused stone
- Cleaning and maintenance
Naturally using reclaimed materials will create more character in sites, and landscapes which are embedded in their context and history. The time for perfect clean lines and square edges on concrete paving is disappearing in lieu of the charming materiality of the past.
Hello@carbonpositivelandscapes.com
More posts like this
