Concrete is a ubiquitous construction material, but it is vital that we reduce its carbon emissions. This requires the industry to embrace a less rigid approach to innovation and specification, says Paul Astle of Ramboll

Paul Astle

Standards and specification documentation are an incredibly important part of the design process within the built environment, providing a common framework around which design is executed and information produced. This in turn builds trust and reliability and improves the exchange of information. 

The standards underpinning structural design and concrete use have been crafted over decades; indeed, the earliest national code for reinforced concrete structures was published in 1934. Today, we use an extensive suite of sophisticated and harmonised design and material codes.

There are standards for almost every aspect of construction. When it comes to the use of concrete, a British Standard Institute search returns 1,903 construction standards. It is a material that has been thoroughly codified, which has no doubt encouraged the adoption of concrete as the ubiquitous material that it is today; a standard can be found for every aspect of its use. 

However, it is the extensive nature of these standards – which have been established over decades often following the discovery of a problem –that has led to inherent conservatism in their embrace of new approaches and a glacial pace of change. This is not compatible with the urgent need to tackle the climate emergency, and particularly the embodied carbon associated with concrete, by unlocking new approaches, technologies or materials.

New concrete technologies can be used with current standards, but appropriate testing is needed to demonstrate compatible performance for a given project. This can be both costly and time-consuming – a problem when there is little time in the programme. 

We must either change the formal standards more quickly, which can be costly, or the industry needs to be able to embrace non-standard approaches without fear of increased risk

Some in the industry have sought to assist potential specifiers with the development of their own Publicly Available Specification (PAS) to accelerate the potential adoption and formal standardisation of one type of non-conventional cement known as alkali activated cementitious materials (AACMs). However, the insurance industry, building inspectors and indeed clients often mandate the reassurance and perceived protection that comes with being able to state that an asset has been designed and constructed in accordance with a tried and tested formal standard. 

We must either change the formal standards more quickly, which can be costly, or the industry needs to be able to embrace non-standard approaches without fear of increased risk.

Specification documentation also plays an important role in how standards are used. They translate the technical requirements of multiple standards into the project-specific requirements, which typically form the contractual information, meaning the requirements of a specification become contractually binding. As such, this can also lock in the use of specific standards and preclude the adoption of novel approaches. 

This is not to suggest that this is the intention of specifications or their authors; like standards, they have been developed and crafted to protect all parties by clearly setting out the necessary works.

As a result of the slow pace of change in standards and specification approaches, we find ourselves in a position where concrete is being specified in accordance with best practice, but could easily have lower carbon if there were more options and/or flexibility in how the concrete could be specified.

One example of this relates to composite cements, a class of material which permits multiple cement replacements to be used in a combination with Portland cement. This allows us to reduce embodied carbon while using often limited cement replacements more efficiently. 

Composite cements were codified in BS EN 197-5 published in May 2021. However they are currently not included in the concrete code, BS 8500-2 Specification for constituent materials and concrete.

Of course, we need to carry out the necessary validation, but once completed we rapidly need to be able to adopt new technology

The Mineral Products Association has carried out tests on a range of low-carbon EN 197-5 cements and their performance was successfully validated and characterised against reference cements. Proposals to include the new cements as general-purpose cements in BS 8500 were accepted by the British Standards committee, and a revision of BS 8500 is currently underway, though this is unlikely to be published until 2023. 

Given that this timeframe was for familiar cement replacement materials used in new proportions, for entirely new cements the timeframe would clearly be even longer. Of course, we need to carry out the necessary validation, but once completed we rapidly need to be able to adopt new technology.

Work is underway in the industry to embrace an alternative approach. Following its launch of the low carbon concrete routemap, the Green Construction Board’s low carbon concrete group has progressed with the potential development of a “flex standard” for concrete. This would make it easier to adopt non-conventional approaches while still providing a rigorous framework for performance in which clients and specifiers can have confidence. 

Such a standard will probably not be published until 2024. However, if this is coupled with a more open form of specification – one based on performance rather than being prescriptive – these complementary strategies could unlock the potential to make immediate carbon savings and accelerate the adoption of new technologies.

As with all the challenges we face in the climate emergency, the solutions to reducing carbon in concrete are complex and multi-faceted. The evolution of our approach to standards and specification is certainly an important element, but so too is the need to change our attitude as an industry and how we deal with risk for those who pioneer new technologies to reduce carbon.

Paul Astle is building structures sustainability lead at Ramboll