UKRI SBE0084

Written evidence submitted by the UKRI Interdisciplinary Circular Economy Centre for Mineral-based Construction Materials

About us

The UKRI Interdisciplinary Circular Economy Centre for Mineral-based Construction Materials (ICEC-MCM) is an academic research centre hosted jointly by UCL, the University of Leeds, Loughborough University, University of Sheffield, Lancaster University, Imperial College and the British Geological Survey.  It is supported by 25 world-class investigators and more than 40 industry partners. With a focus on built environment infrastructure, the ICEC-MCM aims to develop a better understanding of materials flows and impacts, and systems and technologies for more efficient use and recovery of mineral resources, to reduce UK construction minerals extraction and the generation of mineral waste.

The ICEC-MCM is funded by UKRI and EPSRC through the Strategic Priorities fund and is led by Prof Julia Stegemann (UCL).

Contributors to this submission

The following individuals contributed to this submission:

• Prof Julia Stegemann (UCL)
• Dr Rachel Capon (Mineral Products Association)
• Prof John Provis (University of Sheffield)
• Dr Ornella Luorio (University of Leeds)

Summary of key points

Our management of the built environment has major social and economic impacts.  Sustainability is not limited to concerns with climate change, and the built environment is associated, for example, with significant destruction of natural habitats[1]. The government’s net zero commitment provides an opportunity to change the way we build, use, repurpose and deconstruct the built environment to better meet the joint needs of the diverse aspects of the environment, economy and society, focussing not only on the materials consumed but also whole life performance. Such an approach could embed systems thinking, circular economy approaches.

Decisions about the sustainability of different options are difficult to make intuitively, but life cycle assessment (LCA), which considers “cradle-to-grave" environmental impacts, is a quantitative tool that can be used to compare the sustainability of different options.  The Committee on Climate Change Sixth Carbon Budget recommends that government should work towards introducing a mandatory minimum whole-life carbon standard for both buildings and infrastructure.[2]

It is important that LCA is conducted in a transparent, auditable manner, so that impacts of any assumptions, e.g., about the underlying data, or aspects that have been included, are clearly apparent.

Response the Committee’s questions

2.      How can materials be employed to reduce the carbon impact of new buildings, including efficient heating and cooling, and which materials are most effective at reducing embodied carbon?

It is tempting to categorise different materials as more or less sustainable, but it is important to also consider the performance of materials in different circumstances and their suitability for different applications as well as the materials themselves. For example, using timber in small buildings may lead to lower overall embodied carbon, but for larger structures, much greater quantities of timber are required to achieve the same levels of strength provided by other materials (such as steel or concrete). Comparison of the CO2eq emissions and other aspects of sustainability of materials in a particular application requires transparent, systematic, quantitative assessment, e.g., through the use of Life Cycle Assessment (LCA).

It is difficult to envisage a built environment that doesn’t use substantial quantities of concrete.  Concrete contains around 10-15% by mass of cement. Cement production is currently carbon-intensive, accounting for ~7% of global carbon dioxide emissions[3], but UK cement production has a already delivered a 53% reduction in absolute carbon dioxide emissions since 1990 – decarbonising faster than the UK economy as a whole. The decarbonisation in UK cement production is due to a combination of actions by industry, to use more energy efficient kilns, switch fuels from traditional coal and petcoke, and use pulverised fuel ash (PFA) and ground granulated blast furnace slag (GGBS), whose emissions are attributable to the energy and steel industries, as supplementary cementitious materials as a replacement for cement clinker. The UK concrete and cement industry has a roadmap to beyond net zero where the Mineral Products Association outlines seven decarbonisation levers for reaching net zero[4] .

Reduction of embodied carbon thus depends not only on material choice, but also on use of lower-carbon manufacturing and transport processes, lean building design to reduce material use (as well as operational energy), and enable reuse of structures and components at high value (Design for Deconstruction and Reuse, DfDR), at end of service life.  These strategies apply to all materials.  Going beyond “passive” buildings with net zero energy consumption, there is a vast potential for “active” buildings, with integrated energy generation, which could also support biodiversity.

Compared to other construction materials concrete is low maintenance and has a long in-use lifetime. Internal concrete frames designed to achieve 50 years durability, require no additional resource or design requirements to achieve a predicted durability of 100 years.[5] Retaining and reusing existing concrete frames offers an immediate opportunity to significantly reducing the carbon expenditure of construction. There are numerous examples of new life being breathed into existing concrete framed buildings with associated carbon savings, such as Centre Point and Elizabeth Court, Winchester.

Concrete can be highly durable but is not always designed for durability.  Concrete mix design can be optimised to increase durability, reduce carbon footprint, resource demand and waste generation by considering cement composition and content, aggregate grading and durability. As described above, replacing clinker with PFA and GGBS has led to reductions in the carbon emissions associated with cement production/reduced the need for mining minerals for clinker and uses otherwise waste materials. However, UK supplies of PFA and GGBS are limited[6]. Wastes (for example from mining or construction, demolition and excavation) are potential alternatives with large stockpiles and continuing generation in the UK and worldwide. Utilisation of wastes as binders and aggregates to make more resource-efficient concrete can also have technical performance benefits, if the mineral wastes are pre-processed and blended to result in features to enhance long-term concrete performance.

3.      What role can nature-based materials play in achieving the Government’s net zero ambition?

The most obvious nature-based material in the built environment is arguably timber, and there have been significant technical advances to develop engineered timber products of high strength.  Since each material processing step increases associated CO2 emissions, there may be significant emissions associated with these products, as well as environmental impacts associated with the glue used in them.  Furthermore, timber harvesting, even with replanting, can have extremely damaging impacts on natural capital (biodiversity) , and it is not clear to what extent our planet’s forests can meet the many demands placed on them (also for other purposes, such as replacement of plastic packaging).[7],[8]

Again, decisions about materials choices need to be backed up by rigorous and transparent evidence, and systematic quantitative comparison of the options, e.g, through life cycle assessment (LCA) of “cradle-to-grave" environmental impacts.

In any use of materials, it is important to enable their cycling at high value.  In the example of timber, waste from construction and demolition is usually down-cycled for use at low value (e.g., as single-use animal bedding, or for energy recovery).  Greater value could be recovered from timber waste by using it in place of virgin timber to make engineered timber products, such as cross-laminated secondary timber (CLST)[9]

4.      What methods account for embodied carbon in buildings and how can this be consistently applied across the sector

In general, the problem with including embodied carbon in standards is the lack of commonly agreed upon carbon calculation methodology, large enough databases of buildings, and finally realistic assessments of what is feasible given design constraints.

There have been moves in that direction, for example the data-gathering efforts by researchers at MIT[10] and more recently by the IStructE.[11]  Once there is a consensus on those aspects, it will be relatively easy to set targets and rate buildings.

Several organisations have already developed methodologies for measuring embodied emissions. These include:

•              UK Green Business Council[12]
•              RIBA[13]
•              London Energy Transformation Initiative[14]
•              GLA[15]

Relevant standards include:

•              PAS 2080 is a global standard for managing infrastructure carbon
•              BS EN 15804 provides core product category rules relating to Environmental Product Declarations for construction products and services. Importantly, EN 15804 was amended in 2019 and now requires most construction products, and all timber products, to declare carbon emissions through the whole life cycle. It is no longer permissible to report only the embodied carbon during the manufacturing and construction phase.

The biggest issues with the standards tend to be allocation rules, system boundaries and transparency, so there is a need for clear product category rules (PCR). It is also important that construction professionals are trained and skilled in use of LCA and that they understand the characteristics of and use up to date data for each material, to enable a reasonable comparison of materials.

5.      Should the embodied carbon impact of alternative building materials take into account the carbon cost of manufacture and delivery to site, enabling customers to assess the relative impact of imported versus domestically sourced materials?

Yes, accounting of impacts across all life cycle stages, including the supply chain, is necessary for informed comparison of products (which may be materials or buildings).

The embodied greenhouse gas emissions related to construction materials are significant, in some cases accounting for 50% of whole-life emissions (excluding internal fit-out).[16] It is clearly important that these are taken into account. However, it is also important that whole life-cycle emissions are considered too. The data for carbon associated with maintenance, long life and realistic end of life scenarios requires further development.

Conventional Life Cycle Assessment (LCA) takes a static systems approach when assessing impacts. A consequential LCA can help to better understand changing practices in moving to a circular economy approach (for example factoring in service life extension, closed-loop recycling of materials and industrial symbiosis). Consequential LCA can be used to gain insights into the trade-offs associated with different circular life cycle options for materials that may facilitated better informed decision making.

May 2021