Back to Previous

Beyond Portland cement: Low-carbon alternatives

Tag
Author
Date published
Price

This guidance, authored by Eugenie Sentucq and Max Clayton, details how the amount of embodied carbon in concrete can be reduced though the use of alternatives to cement. Max runs a design team at Structure Workshop and together with Eugenie, they have been instrumental in developing the company's low-carbon approach.

Portland cement production is already responsible for over 8% of global carbon emissions1, yet its production is set to increase by 25% by 20501  - a period in which rapid global decarbonisation is urgently required.

Current methods of reducing the amount of embodied carbon in concrete – replacing cement with slag and fly ash – are inadequate due to their small and declining supply, but there are promising alternatives that can be developed and used to meet these challenges.
 



Clinker substitution (the problem with GGBS and PFA)

An effective way of reducing the carbon associated with concrete construction is to replace a substantial portion of clinker in the cement mix with supplementary cementitious materials (SCMs). Today these are primarily ground granulated blast furnace slag (GGBS) or pulverised fly ash (PFA).

PFA and GGBS are both industrial waste products, so their use in cement reduces the carbon emissions from clinker production. Their effect on concrete is well understood, with high strength and durable mixes being readily available.

The problem with GGBS and PFA is one of supply. The amount of slag available globally is only 5-10% of cement production2, with a similar figure for PFA. As by-products of high-carbon industries, their availability will decrease further as coal power stations are shut down and more steel is recycled over the coming years.

Almost all of the GGBS and PFA currently produced in the UK is already being used, primarily in concrete, so specifying these SCMs does not necessarily help to reduce construction sector emissions. In addition, most slag production is localised to a few iron-producing countries, whereas cement demand is far more pervasive. To meet the massive demand for cement globally, new SCMs are needed which are both abundant and widespread.
 

Alternative SCMs

Cementitious materials are broadly made up of calcium, silicon, and aluminium oxides in various proportions. Unlike calcium, natural sources of silicon and aluminium are not present as carbonates, and therefore do not undergo decarbonation when calcined for cement.

One plentiful and readily available raw material is clay. Clays with a high kaolinite content, rich in silica and alumina, have been shown to be highly pozzolanic if calcined at 700-850°C2. They exist worldwide in massive quantities, so vast as to be effectively unlimited1. Another abundant SCM is limestone, which can be ground for use at modest ratios in cement in its uncalcined state.
 



Limestone calcined clay cements (LC3)

A combination of calcined clay and limestone can directly replace a high proportion of Portland clinker in cement. This is known as Limestone Calcined Clay Cement, or LC3.

In European standards, ternary blends such as CEM IIB-M(Q-LL) already allow for a clinker content of just 65%, with calcined clays (Q) and limestone (LL) making up the rest. There is a proposed extension to the standard that will allow clinker content to be reduced to 50%, but this does not currently include calcined clay as an approved substitute.  

A blend comprising just 50% clinker with 30% calcined clay, 15% limestone and 5% gypsum has been shown to produce cement with mechanical properties comparable to a CEM I blend from seven days, with better durability and with a 30% reduction in CO2 emissions4.  This technology has already been successfully trialled in in Cuba and India, including a concrete demonstration house in Jhansi, India which resulted in a 15.5t carbon saving5.  It should be straightforward to include calcined clays in higher quantities in future technical standards.  
 



The commercial availability of calcined clays is currently limited compared to the sheer quantity needed, as the cement industry is currently geared towards Portland cement production, but the raw materials are sufficiently abundant. Calcined clay limestone cements have the potential to dramatically expand the use of SCMs as partial clinker replacement and make significant contributions to CO2 emission reduction.
 

Alkali-activated materials / geopolymers

In the long term, alternative cementitious materials have the potential to replace up to 100% of Portland clinker, GGBS and PFA in cement mixes. Some raw materials high in alumina and silica include volcanic rocks (common in southern Europe, the Andes and the Middle East), lateritic soils (common in the tropics) and clays high in kaolin (common worldwide). These raw materials are widely distributed and exist in quantities vastly exceeding global cement production6.  

They can be heated and crushed to form a powdered precursor for use in cement. The resulting product is known as an alkali-activated material, or a geopolymer when minerals lacking calcium are used. When combined with a strong alkali ‘activator’, the precursor reacts to form a hardened binder. In the case of geopolymers, this binder consists of aluminosilicate phases, rather than calcium hydrates present in Portland cement, but with similar properties. This technology may play a critical role in achieving the emissions reductions required of the construction industry.

Various commercial alkali-activated cements have already been developed, such as DB Group’s Cemfree and Cemex’s Vertua which are available in the UK today, but both are reliant on GGBS as the precursor. In Northern Ireland, Banah UK Ltd developed a geopolymer cement based on calcined clay, and claimed a 75% reduction in carbon emissions, but the company shut down in 2019 for commercial reasons.

Commercially available, low-calcium geopolymer cements based on natural resources have the potential to dramatically reduce global concrete emissions, but they are still a nascent technology with significant R&D required to create a viable product.
 

Summary

Reducing construction industry emissions by the extent necessary to limit warming to 1.5°C will require a huge increase in the use of alternative cements and a shift away from Portland clinker, GGBS and fly ash, in addition to lowering the overall demand for cement where possible. While these new materials currently have a limited production capacity compared to the vast quantities required, it is important we educate ourselves and be prepared to incorporate these alternative cements into our designs as they become available. Engineers can help create a market for, and build acceptance of, these alternative cement products. The future of the cement industry could conceivably involve the development of a wide range of cements based on locally available, highly abundant, low carbon natural resources, with massive reductions in embodied carbon as a result.


References

1 Karen L. Scrivener, Vanderley M. John, Ellis M. Gartner (2018) 'Eco-efficient cements: Potential economically viable solutions for a low-CO2 cement-based materials industry', UN Environment
2 Karen Scrivener, Fernando Martirena, Shashank Bishnoi, Soumen Maity (2018) 'Calcined clay limestone cements (LC3)', Cement and Concrete Research, 114, pp49-56
3 Jannie S. J. van Deventer, Claire E. White, Rupert J. Myers (2020) 'A Roadmap for Production of Cement and Concrete with Low‑CO2 Emissions', Waste and Biomass Valorization (2020)
4 Maria C.G. Juenger, Ruben Snellings, Susan A. Bernal (2019) 'Supplementary cementitious materials: New sources, characterization, and performance insights', Cement and Concrete Research, 122, pp257-273
5 LC3 in use: Applications
6 John L. Provis (2018) 'Alkali-activated materials', Cement and Concrete Research, 114, pp40-48

 



 

Related Resources & Events

Course
A bridge over a dry river bed

Net-zero structural design

This course is designed to enable you to design structures with net zero emissions. Delivered as a series of interactive online sessions across five weeks.

Date – 9 November 2023
Location – Online
Price – £485 - £745 + VAT
Course
Dark underground parking garage

Deep basements

This course gives guidance on the key considerations when planning the construction of deep basements. It covers using both embedded wall bottom-up and top-down construction in accordance with Eurocodes 2 and 7.

Date – 12 October 2023
Location – Online
Price – £275 - £425 + VAT
Course
<h4>Timber workshop: design through worked examples</h4>

Timber workshop: design through worked examples

This one-day, online advanced practical workshop will teach complex timber engineering through worked examples. It encourages problem-solving through teaching tools and group discussion.

Date – 6 October 2023
Location – Online
Price – £275 - £425 + VAT
Course
<h4>Structural engineering with bamboo</h4>

Structural engineering with bamboo

This course will equip attendees with practical knowledge about structural design with bamboo stems (culms). The course considers aspects of concept design, detailed design and durability by design.

Date – 26 September 2023
Location – Online
Price – £275 - £425
Course
<h4>Structural engineering for non-structural engineers</h4>

Structural engineering for non-structural engineers

This one-day, online course is designed to offer an understanding of structural engineering in relation to buildings to construction industry professionals.

Date – 20 September 2023
Location – Online
Price – £275 - £425 + VAT
Course
A bridge over a dry river bed

Net-zero structural design

This course is designed to enable you to design structures with net zero emissions. Delivered as a series of interactive online sessions across five weeks.

Date – 7 September 2023
Location – Online
Price – £485 - £745 + VAT
Webinar
<h4>Circular economy and reuse: guidance for designers - Book launch webinar</h4>

Circular economy and reuse: guidance for designers - Book launch webinar

The IStructE is pleased to announce their latest publication supporting the climate emergency agenda, Circular economy and reuse: guidance for designers.

Date – 11 July 2023
Location – Online
Conference
<h4>Young engineers conference 2023</h4>

Young engineers conference 2023

This annual conference brings together the next generation of construction leaders to discuss critical issues facing the industry and make connections. The 2023 theme is ‘Pathways to positive change’

Date – 7 July 2023
Location – The Institution of Structural Engineers
Price – £10.00 - £50.00
Webinar
Concrete structure

Analysis and strengthening of concrete buildings: common construction types 1950 - 1985

The first webinar of a 6-part series on the analysis and strengthening of concrete buildings built from 1950 – 1985

Date – 4 July 2023
Location – Online
Price – £45 - £70 + VAT
Webinar
Unfired earth bricks can be seen in organised lines. Copyright: MASS Design Group, 2023.

Novel materials: low-tech solutions

The first webinar of a 6-part series on novel materials focuses on low-tech construction materials solutions such as structural stone, unfired mud bricks and roundwood timber.

Date – 27 June 2023
Location – Online
Price – £45 - £70 + VAT
Conference
looking up to sky surrounded by building

Climate emergency e-conference 2023

Join this e-conference to hear about leading industry initiatives to combat the climate and biodiversity emergency

Date – 22 June 2023
Location – Online
Price – Free
Lecture
Areal view of Lewes Castle, showing a broken wall. Copyright: The Morton Partnership, 2023

The effects of the changing climate on historic structures

Engineer Sarah Tattersall talks about the causes behind the collapse of a historical structure and the repair interventions that were carried out by her team.

Date – 21 June 2023
Location – Online
Price – Free
Guidance
<h4>Circular economy and reuse: guidance for designers</h4>

Circular economy and reuse: guidance for designers

This new guidance is an essential read for any built environment professional developing new (or reusing existing) structures today. Across four principal sections it explains why the adoption of circular economy principles is critical.

Date – 19 June 2023
Author – P Gowler et al
Price – £32.50
Lecture
<h4>Re-engineering the future – zero carbon</h4>

Re-engineering the future – zero carbon

Learn about the latest engineering research helping to make businesses in all sectors more sustainable and profitable in the coming years

Date – 7 June 2023
Location – University of Greenwich
Price – Free
Lecture
<h4>Embodied carbon</h4>

Embodied carbon

The second of this year’s training gyms looks at what embodied carbon is, how it is measured, and how it can be reduced on projects.

Date – 6 June 2023
Price – Free