The UK government has commissioned the trade body representing the concrete industry to determine the amount of atmospheric carbon dioxide captured in concrete buildings and infrastructure in a move critics have described as "like the fox guarding the henhouse."

The project, announced last month, will determine how much CO2 is reabsorbed into concrete and the impact this has on the UK's overall carbon emissions.

The Department for Business, Energy and Industrial Strategy (BEIS) has awarded a tender for the work to the Mineral Products Association (MPA), a body that represents manufacturers of materials including concrete, cement and asphalt.

"The project will create a methodology that will inform the UK’s greenhouse gas inventory and the UK’s national and international reporting obligations on climate change," said the MPA.

The news was greeted with concern by some observers with professor Michael Ramage, director of the Centre for Natural Material Innovation at Cambridge University, describing the project as a "red herring".

"We’re concerned about the MPA modelling the carbonation of concrete for BEIS as they are not an independent body," said Ramage. "It is like the fox guarding the henhouse."

"If the UK are to produce a robust model it must be subject to fully independent external peer review by academics, as a minimum," Ramage said. "We don’t much like the idea of BEIS taking advice from MPA on this topic."

Appointing the MPA was akin to "the NHS commissioning British American Tobacco to conduct cancer research," Ramage added. "They can’t possibly be independent."

Cement industry responsible for eight per cent of global CO2 emissions

The cement industry, which produces a key ingredient for concrete, is the world's biggest single emitter of CO2. A landmark 2018 report by Chatham House found that it is responsible for around eight per cent of global emissions.

However, some of the carbon emitted during cement production is later reabsorbed by cement and concrete used in construction projects. The surface of the material draws in CO2 over time via a process known as carbonation.

"Carbonation is a process that occurs naturally in concrete where hydrated minerals react with carbon dioxide from the air to form calcium carbonate," explained the MPA.

This "cement carbonation sink" absorbs an estimated 200 million tonnes of carbon worldwide every year, according to the IPCC climate report published last summer ahead of the Cop26 climate conference.

New project to help calculate impact of cement carbonation

This was the first time that concrete's potential as a carbon sink was acknowledged by the IPCC. However, there is no internationally recognised way of calculating cement carbonation or working out its impact on a nation's carbon emissions. BEIS and MPA hope their project will help fill this knowledge gap.

The tender for the project was issued last May. According to the brief, the project "aims to improve our understanding and the quality of historic emissions, reduce uncertainties in emissions estimates, and improve our ability to assess progress towards international and national targets".

The UK cement industry has released a roadmap setting out how it could become net-zero by 2050. But doctor Richard Leese, director of industrial policy, energy and climate change at the MPA, said that this plan does not rely on using carbonation figures to offset emissions.

“Delivering net zero concrete and cement production in the UK is not reliant on carbonation," said Leese.

"This natural carbonation has previously been overlooked by national and international carbon accounting but can undoubtedly contribute to helping the industry remove more CO2 from the atmosphere than it emits, especially when carbonation can be enhanced or accelerated."

“By assessing exposed concrete used in buildings to bridges, this important research will help improve UK carbon accounting and provide an accurate assessment of carbonation across the lifecycle of the built environment," Leese added.

"It could also shape how future buildings and infrastructure are designed, used and improve the subsequent use of demolition material to act as carbon sinks and accelerate the C02 uptake process.”

IPCC report estimated around half of cement CO2 emissions are reabsorbed

Mikaela DeRousseau, programme manager at US nonprofit Building Transparency, welcomed the project but pointed out that carbonation only recaptures a "small fraction" of emissions caused by concrete.

"MPA’s efforts to develop a better way to model carbonation are exciting and will help improve estimates of carbon sequestration in concrete infrastructure from a national inventory perspective," said DeRousseau, whose organisation aims to help the construction industry reduce embodied carbon in buildings.

Last year's IPCC report estimated that around half of the carbonate emissions from cement production are reabsorbed by the material when used in buildings and infrastructure.

However, carbon emitted when limestone is burned to make cement only accounts for a portion of total emissions from the industry.

"This research will likely confirm that the sequestration of carbon dioxide in concrete is a small fraction of the total carbon dioxide emitted during the life cycle of concrete," DeRousseau said.

Speaking to Dezeen last summer, Cambridge University materials scientist Darshil Shah said that the IPCC's recognition of concrete as a potential carbon sink meant that climate change is "is worse than we thought".

"Cement and concrete are not carbon sinks," Shah said. "They are net sources [of CO2]. Carbonate emissions, or process emissions, are only a fraction of the emissions related to cement production and use."

"They exclude the more substantial fossil-fuel energy emissions associated with cement production, they ignore CO2 emissions from the manufacturing of concrete and mortar and construction of buildings, and exclude any fossil-fuel emissions associated with deconstruction of the concrete structures."

Shah also said that "cement carbonation requires very specific conditions" including humidity of between 40 and 80 per cent and open-air conditions.

"Submerged or buried concrete or concrete will not undergo carbonation," he said, adding that "concrete carbonation happens at an extremely slow rate: an average of one to two millimetres per year."