Opportunities for Material Efficiency

Until recently, much of the research and innovation on sustainable construction has been focused on the operational emissions associated with the building, particularly on improving thermal performance. However, there is increasing recognition that capital emissions, those emitted during the manufacture of construction materials and those embodied in the materials themselves, are of similar importance. As heating systems are electrified and countries decarbonise, their electricity generation and the emissions associated with heating and lighting decrease. This in turn increases the relative importance of capital emissions¹. In addition, the lifetime of a building determines the split between operational and capital. Operational emissions are often calculated over the entire design life, however many buildings end up being demolished sooner than planned². Concrete and Steel are the main source of capital emissions, and these industries are working towards decarbonisation, but rely heavily on carbon capture and storage to reach their targets^3,4. Other sources recognise the need for material efficiency measures, but do not predict that they will be implemented in time to meet 2050 net zero targets⁵.

Early research by the ACORN team has highlighted the importance of categorising the opportunities for material efficiency in construction to avoid double-counting wherever possible. Areas where there are opportunities to reduce waste and improve efficiency in concrete construction are:

• Choice of Structural Form: Choice of grid size, length of span etc greater than required
• Overdesign: Design specifying more material than required for structural purpose (e.g. prismatic beams)
• Overspecification of Structure: Structure designed for loads greater than actually experienced
• Overspecification of Materials: Choice of materials with greater strength than required
• Over-Ordering: Ordering materials in excess quantity than required for construction (e.g. to avoid running out)
• Over-Delivery: Delivery of materials in excess quantity or specification than ordered (e.g. overstrength concrete)
• Onsite Waste: Materials delivered to site but not used for construction
• Over-binding: Concrete delivered with same strength performance but excess binder index
• Excess Clinker: Concrete delivered with same binder index, but a greater proportion of clinker than required
• Efficiency of Clinker Plant: Clinker produced at a plant below the best-available-technology
• Efficiency of Clinker Production: Clinker produced while plant is operating below best-observed performance
• End of Life Recovery: Emissions resulting from (or mitigated by) treatment of waste at end-of-life

The estimated improvements achievable varies depending on material source, construction stage, and construction process. One of the biggest opportunities is in the Overdesign category, where waste can be as high as 50%. It is here that the ACORN project can deliver substantial advantages over conventional processes and designs.

The research team are not alone in seeing the huge opportunities for cost and carbon reduction, and productivity increase, that an ACORN approach can deliver. The project is working closely with its 12 Industry Steering Partners and another 12 Industry Project Affiliates, companies of all sizes spanning the entire AEC industry who have pledged active support for the project’s vision. If your company would be interested in signing up (for free) as an ACORN Affiliate, please get in touch via acorn@automated.construction or check out the rest of our website.

Don't Ignore Process-based Carbon Dioxide Emissions

One of the key questions when it comes to sustainability and the construction industry is what proportion of the emissions associated with a building can be ascribed to the materials used in its construction versus the energy used to heat and light the building during its life.

Many factors and assumptions can affect the conclusion one comes to when trying to tackle this question, including the lifetime of the building itself, the future state of our electricity grid, and whether it matters when during a building’s life the emissions are generated.

In this post, we examine a statement in the recent CEMBUREAU roadmap (2020) shown in Figure 1 below that “72% of CO2 total emissions related to an average building come from the energy used during its working life”. This seems to suggest that embodied carbon makes up a proportion of the impact than other reports might suggest (Material Economics, RICS, LETI).

Figure 1: CEMBUREAU Cementing the European Green Deal p. 31

The source quoted by CEMBUREAU is a World Green Building Council report from 2019, which states:

“Currently, buildings account for 39% of energy related global CO2 emissions2, demonstrating the importance of the building and construction sector in fulfilling these ambitions [to deliver the Paris Agreement]. Of this sector contribution, 28% comes from operational carbon with 11%3 arising from the energy used to produce building and construction materials, usually referred to as embodied carbon”

The WGBC report states that buildings account for 39% of energy related global CO2 emissions, and that of this contribution 28% comes from operational carbon, and 11% from the energy used to produce construction materials. Twenty-eight percent out of 39% gives the 72% operational emissions quoted by CEMBUREAU.

However, the key phrase is that these are energy-related CO2 emissions. As a footnote to the WGBC article states, this does not include any process–related emissions. In the case of cement, emissions from the chemical process of clinker production make up approximately half of total emissions. Excluding these from the embodied emissions of the building is misleading, particularly as the CEMBUREAU report refers to “total emissions”.

The reader of the CEMBUREAU report is left with the impression that embodied carbon is much less important than operational carbon, because the numbers used are not telling the whole story. When examining the operational to embodied carbon split of construction using concrete, we must not ignore the process-based carbon dioxide emissions.

Figure 2: World Green Building Council 2019: Bringing embodied carbon upfrontp16.