Concrete technology tracker

Authors: Paul Astle (Ramboll), Tom Dillon (Ramboll), Will Arnold (IStructE), Tim Forman (University of Cambridge)
Specialist technical contributor: Dr Fragkoulis Kanavaris (Arup)
Reviewers: Niamh McCloskey (Curtins), Duncan Cox (Thornton Tomasetti)

1.  Introduction

Many current and emerging lower carbon concrete technologies available in the UK market have lower embodied carbon associated with them than Portland cement (PC)-based concrete, which will be referred to as ‘conventional concrete’. These technologies have been assessed with a focus on embodied carbon, without considering wider technical and sustainability benefits (eg resistance to extreme temperatures, revalorisation of construction waste, etc).

Behind drinking water, concrete is the most used man-made material on earth, with 14 billion m³ produced each year. As a result, the production of cement, the active binding agent in concrete, accounts for around 7% of global CO₂ emissions. While concrete production emissions arise from a range of sources, cement production is responsible for almost 60% of the embodied carbon in reinforced concrete. Thus, with 2050 rapidly approaching, action must be taken to reduce emissions and realise net-zero commitments. To address this, many companies are developing lower carbon concrete technologies. However, publicly available information about these technologies is often limited and inconsistent, making it difficult to draw comparisons with conventional concrete.

To address this knowledge gap, more than 20 companies marketing lower carbon concrete technologies have been contacted to gain an understanding of their current maturity and expected developments by 2030. The authors have sought to assess each technology objectively based on the information provided by the individual companies, though it should be noted that this information has not been independently verified.

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Figure 1: Lower carbon concrete is a rapidly growing field of research

While the study focusses on the deployment of technologies in the UK market, many technologies are expected to be at a similar level of readiness in other regions. Engineers outside the UK are encouraged to make enquiries within their local market. Additionally, while many of the technologies are intended for use in building structures, a broad range of technologies has been considered, with applications in civil engineering, mass concrete, or other non-structural contexts such as paving and blockwork.

Based on the companies’ feedback, 13 technology streams have been identified as alternatives to conventional concrete which are expected to reach market deployment (if they have not already) between now and 2030. The terminology used to describe each technology stream is aligned where possible with research from the University of Cambridge.  Each technology stream has been assessed in terms of:

• Expected embodied carbon of a concrete produced using that technology compared to conventional concrete
• Its current state of technological/ commercial maturity and expected development to 2030 in relation to the UK market (as with all forecasting, this is indicative based on available data)
• Additionally, a summary of key issues for designers to consider has been included, covering code compliance, applications, and links to example products/ companies. Follow the links for more information and case study project examples where available

Given the range in technology/ commercial readiness of these technologies, it is not practical to provide a detailed assessment of cost at this stage. It is expected that most technologies will be initially more expensive than conventional concrete as, for example, they require different raw materials without existing supply chains at scale or demonstration by testing for use on a project. However, it is assumed that as use of these technologies becomes more widespread, economies of scale will reduce this premium. Additionally, the expected implementation of government/ industry regulation limiting embodied carbon will improve the viability of schemes using these technologies.

The list of technology streams and companies/ products presented is far from exhaustive – this is a fast-moving space with constant developments. However, this webpage aims to provide a representative snapshot of current and emerging lower carbon concrete technologies, and how they are expected to develop 2030. The page will be maintained and reviewed in response to further innovation and information.

If you would like to suggest additions to the page, please contact us.

 

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Figure 2: Understanding the possible uses of new concrete technologies is critical

2.  The technology streams

This section provides a summary of the 13 technology streams, including a brief description for each, with key issues that should be considered by designers wanting to specify these technologies and example products/ companies. Where the products are not available in the UK, their country of origin has been noted.
 
Table 1, and Figures 3 and 4, show an overview of the technology streams, summarising their expected embodied carbon and UK technology/ commercial readiness. See Section 3 for details about how these assessment criteria have been defined.
 
There is no single technology stream – “silver bullet” – that is sufficiently scalable to eliminate global concrete production emissions. This sentiment is well summarised in the following quote from The 3Cs of Innovation in Low-Carbon Concrete, a report from the RMI examining decarbonising solutions across the clinker, cement and concrete production stages:

“Note that these innovations do not represent mutually exclusive decarbonisation pathways. A 1.5°C-aligned transition will likely rely on most or all of them. Given that carbon capture technologies thus far typically have high energy requirements, high up-front capital investment, large-scale infrastructure network requirements, and long permitting times, it is important to leverage all other technology solutions across the value chain before deploying carbon capture to eliminate the remaining emissions.”

As noted in the quote above, the technologies are not mutually exclusive and it may be possible, and advantageous, to combine multiple technologies. For example, it would be sensible to adopt both technology A1: optimised conventional concrete, alongside the use of B4: SCM – calcined clay. However, any combination of technologies would need to be assessed on a case-by-case basis and advice from the supplier and respective technology companies should be sought.

Additionally, note that these technology streams should be implemented alongside lean design principles, in which engineers maximise material efficiency to reduce concrete volumes as far as possible. Lower carbon material specification is no substitute for efficient structural design.

NB: The term "binder" corresponds to the material or substance that holds together the particles of aggregates (such as sand and gravel) to form a cohesive mass. For example, the typical binder in conventional concrete is portland cement which can be partially or fully replaced with other binders.

 

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Figure 3: Expected embodied carbon of each technology stream

Figure 4 UK technology commercial readiness of each technology stream

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Figure 4: UK technology/ commercial readiness of each technology stream

Figure 5: Concrete being poured in-situ on a building site

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Figure 5: Concrete being poured in-situ on a building site

2.1.  Group A: Conventional concrete

The technologies in this group aim to produce clinker (the active binding ingredient in cement) identical to that used in conventional concrete, using alternative materials or production methods to reduce embodied carbon.
 

2.1.1.  A1: Optimised conventional concrete

This ‘technology’ stream refers to the need to ensure that best practices are undertaken to optimise conventional concrete mix design for embodied carbon. It is not related to a specific technology but is a combination of approaches that can be taken by the supplier. It is not expected, or recommended, that engineers should try to provide detailed specification clauses to optimise concrete for carbon. Rather, this optimisation should be delivered by the supplier following collaboration and discussion with the engineer and contractor as early as possible. It will not be possible to achieve carbon savings in all concretes but, based on the authors' experience, discussions with concrete suppliers to optimise carbon of conventional concrete can lead to immediate savings of between 5-15%.

Reference should also be made to the following guidance:

• Practical specification of lower-carbon concrete
• How can we reduce the embodied carbon of structural concrete?
• Low Carbon Concrete Routemap

2.1.2.  A2: Alternative raw materials

These technologies aim to produce conventional clinker using alternative raw materials that release substantially less carbon during processing than limestone and clay. The two most promising technologies are:

• Calcium silicate: a mineral 100 times more abundant than limestone which can be used to produce clinker without process emissions (60% of total clinker emissions) as there is no carbon to be calcined, unlike the calcium carbonate derived from limestone used to produce conventional clinker. Calcium silicate can be used to produce a binder that is chemically and physically identical to PC
• Recycled cement paste: cement paste is separated from crushed concrete (derived from demolition waste) and processed to make clinker for reuse in new concrete. This method avoids the process and combustion emissions of producing primary clinker, thus substantially reducing embodied carbon. While limited demolition volumes prohibit all concrete being produced via this method, there is scope for significant implementation and global emissions reductions

2.1.3.  A3: Carbon capture, utilisation and storage (CCUS)

The cement and concrete industry have ambitious plans to decarbonise PC production via the use of CCUS technologies. This involves capturing the process and combustion emissions of clinker production at source, resulting in lower carbon PC. The captured CO₂ my then be utilised for chemical processes or permanently stored, typically underground in depleted oil and gas fields. While these technologies are not yet available at scale, there are some pilot facilities, most notably Brevik CCS in Norway. This technology stream involves the capture and storage of emissions from conventional PC production, differing from the technologies in Group C which sequester CO₂ within the concrete itself.

Figure 6: Concrete structures could be used as a form of large-scale carbon storage in the future

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Figure 6: Concrete structures could be used as a form of large-scale carbon storage in the future
 

2.2.  Group B: Clinker replacement

The technologies in this group replace clinker (the main source of carbon in concrete) either partially using SCMs, or entirely using non-Portland cements.

2.2.1.  B1: Traditional supplementary cementitious materials (SCMs)

It is common UK practice for ground granulated blast-furnace slag (GGBS), fly ash (FA) and limestone fines to be used as SCMs to replace the PC in concrete. Silica fume is also used in high strength applications. Typical replacement rates are up to 50% in superstructure elements and up to 80% in buried concrete elements, as per the maximum GGBS allowed for CEMIII/B according to BS 8500. As these materials are industrial co-products and/ or require less processing than PC, they have significantly lower associated embodied carbon. The revisions in BS 8500:2023 allow the increased use of limestone fines, which have very low embodied carbon, as part of a multi-component “ternary” blend, up to a maximum of 20%. This replaces up to 20% of the cement which would otherwise have been either PC or GGBS/FA, reducing carbon without relying on constrained materials¹.
 

2.2.2.  B2: Non-Portland Cement – Alkali activated binders (AABs)

AABs can replace the PC in concrete and are derived from precursors (either industrial co-products such as GGBS and FA, or natural minerals) which are added to an alkaline medium to produce cementitious material, which like conventional concrete is cured via hydration. Unlike SCMs, AABs can be used to entirely replace PC, however their embodied carbon can vary drastically depending on the precursor used.

2.2.3.  B3: Non-Portland Cement – Alternative binders

These technologies include alternative binders such as belite-rich PC clinkers, calcium sulfoaluminate cements (CSAs), magnesium oxide cements, etc. More information can be found in Section 7 – Cements Made from “Alternative Clinkers” – of the UN’s Eco-efficient cements report.
 

2.2.4.  B4: SCM – Calcined clay

Clays are abundant globally and many are suitable for calcination. Kaolinitic clays are most favourable, which when heated and processed form a reactive material known as calcined clay.  Whilst they cannot fully replace clinker, they have the potential to displace huge quantities of PC at a global scale. Historically in the UK, calcined clays have not been as widely utilised as GGBS and FA, however they have had extensive use in other markets such as Brazil and it is possible to buy bagged calcined clay cements in parts of Central and South America. It should be noted that BS 8500 allows a calcined clay-limestone ternary blend within (CEM II/B-M(Q-L)), but the minimum clinker level will be 65%. Future changes to BS 8500 may permit combinations with less clinker.
 

2.2.5.  B5: SCM – Olivine-based SCMs

These technologies utilise olivine, a globally abundant magnesium iron silicate mineral, which through carbon sequestration, can be transformed into silica and magnesium carbonate. Silica can be used as an SCM to replace clinker up to 40%, and as the silica sequesters carbon, a carbon neutral cement can potentially be achieved.   
 

Figure 7: Engineers should expect to specify new cements and concretes this decade

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2.3.  Group C: Carbon sequestration within concrete

The technologies in this group sequester CO₂ within concrete in various ways.
 

2.3.1.  C1: Carbon-sequestering aggregates

This technology does not affect cement, but instead sequesters carbon in the aggregate used in concrete. They are typically sourced from waste streams and given the large volume of aggregate (65-75%) compared to cement (10-15%) in concrete there is scope to produce low or even negative embodied carbon, compared to conventional concrete. 
 

2.3.2.  C2: Carbon injection

This technology involves injecting small amounts of CO₂ into concrete during mixing to increase its strength via CO₂ mineralisation, allowing the cementitious content (and thus embodied carbon) to be reduced for a given concrete strength. These concretes cure via hydration (ie can be cast in-situ) and the injected carbon is sufficiently diffuse that the alkalinity is not reduced significantly, allowing reinforced structural applications. The CO₂ is injected either directly in liquid form, or using a carrier derived from waste streams.
 

2.3.3. C3: Carbonation curing

These alternative binders (ie non-PC based) use minerals or waste products which cure via CO₂ mineralisation in specialised curing chambers. As CO₂ is absorbed during curing, the resultant concrete has low or even negative embodied carbon, compared to conventional concrete.  
 

Figure 8: R&D funding must accelerate cement decarbonisation

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Figure 8: R&D funding must accelerate cement decarbonisation

2.4.  Group D: Other approaches

This group captures alternative approaches to producing lower carbon concrete which do not fit within the other groups.

2.4.1.  D1: Performance enhancing admixtures

This technology stream covers non-standard admixtures which differ from hardening accelerating admixtures that may be used in A1, including:

• Graphene: Improves concrete strength and durability allowing reduction of section size (and thus concrete volume) and reinforcement
• Soil strengthening: Admixtures can be added to excavated soil to produce low-strength (C20/25), poured-earth concrete
• Self-healing concrete: Bacteria within the admixture reacts with water to produce limestone, thus fixing cracks as they form, and extending the lifetime of a concrete structure

2.4.2.  D2: Biocement

Producing concrete using biotechnology involving micro-organisms and feedstock chemicals to bind together aggregate in a process similar to coral growth.

2.5.  Other technologies

Below comprises a list of technologies that the authors are aware of but have not been included above. Some of these are too early in development to discuss expected embodied carbon/ development timelines; other have not yet been contacted or have not responded to the authors at the time of publication. If you have further information regarding these technologies, please contact us.

• BioChar
• EMC Cement
• Carbonaide
• Carbon Upcycling
• SonoAsh
• Partanna
• Terra CO2
• Sublime Systems
• Chement
• Prometheus Materials
• Neustark
• CQuestr8
• Ecocem
• Seamix
• Ferrock

Figure 9: A test block of a novel concrete product

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Figure 9: A test block of a novel concrete product
 

3.  Assessment criteria

3.1.  Expected embodied carbon

These technologies generally aim to provide a lower carbon alternative to conventional concrete. Thus, arguably the most important metric is expected embodied carbon compared to business-as-usual (BAU) conventional concrete. As a basis for comparison, the baseline considered has been set as the A1-A3 embodied carbon of a C32/40 mix with 25% GGBS replacement = 300kgCO₂e/m³. This represents a typical concrete specification in the UK.

The technology streams have been categorised on a scale of Low, Medium, and High expected embodied carbon. This represents the embodied carbon a concrete produced using a given technology stream, relative to the baseline which has been set at the upper limit of the High category. This scale is intentionally vague. Due to the range of maturity of the different technology streams, it is difficult to determine reliable, comparable values for expected embodied carbon in most cases. As technologies develop and are trialled at scale, greater certainty can be attributed to expected embodied carbon values and the granularity of this metric can be revised.

Where technologies are early in development or a technology stream includes a broad variety of technologies, a range has been given for expected embodied carbon (eg Low-Medium) to confer this uncertainty.

This metric considers only the embodied carbon of 1m³ of concrete produced using a given technology stream, it does not assess scalability and quantify how the implementation of a technology stream would affect global concrete emissions (eg GGBS supply is limited by global ironmaking at a level approximately 1/10^th of global cement demand; and recycled cement paste is limited by available demolition waste). Furthermore, the comparison is for concrete only ie the embodied carbon of steel reinforcement has not been considered.
 

3.2.    UK technology/ commercial readiness

While the study focusses on the deployment of technologies in the UK market, many technologies are expected to be at a similar level of readiness in other regions. Engineers outside the UK are encouraged to make enquiries within their local market.

Of equal importance to expected embodied carbon is the maturity of these technologies, given the urgency with which carbon emissions must be reduced. The technology streams have been classified as follows:

• Research and development (TRL 1-7): Establishing theoretical principles and proof of concept at laboratory scale with demonstration in a simulated environment
• Demonstration – (TRL 7-9 / CRI 1): Demonstration in real-world pilot projects and hypothetical commercial proposals
• Market deployment (TRL 9 / CRI 2-6): Fully mature technology ranging from small scale commercial trial to mainstream market deployment

These categories are based on the development stages (and corresponding TRL/ CRI) developed by NASA and adapted to the cement and concrete industry in Low Carbon Concrete Technologies (LCCT): Understanding and Implementation.

Based on the responses from contacted technology companies, the current state of each technology stream’s development has been assessed. However, determining development up to and beyond 2030 is difficult, as the predictions from the companies themselves are inevitably aspirational. A forecast to 2030 has been compiled based on the companies’ responses and the authors’ own knowledge and experience. This forecast is highly indicative and should not be taken as accurate for precisely when each technology stream will be commercially available. However, it provides a user with an idea of currently available technologies, and those that can be expected in the coming years. The rate of change of this research space means forecasting beyond 2030 would be of limited use at this time.