Ecodesign in PracticeEcodesign in Practice is a series of sustainable construction design solutions that can be applied at scale. The solutions are also integrated as data sources in One Click LCA for Buildings and Carbon Designer 3D. We publish an article and associated solutions once every six weeks. Enjoy reading!
Low Carbon Concrete Solutions
A quick guide for design teams and contractors
A checklist for reducing embodied carbon when building with concrete
- Minimize the concrete quantity by design. Optimize structural grids and use material efficient solutions like hollow core slabs.
- Ensure the building adaptability is not jeopardized by the above.
- Minimize the total clinker use in your project by using alternative binders. This also reduces cost.
- Make the case and get buy-in from the developer / investor to implement low-carbon concrete solutions in the project. (E.g. traditional replacements for structure, new ones for paving and such)
- Plan for construction schedule-aligned curing times to allow for longer strength evaluation time when possible.
- Set a low carbon concrete specification as a requirement for purchasing.
- Ask for low-carbon solutions from your suppliers.
- Choose low carbon reinforcement bars, fibres or alternative reinforcement solutions.
- Ask suppliers to back up their low-carbon solutions with EPDs.
- Consider transportation related impacts when making purchase choices.
Why is concrete so carbon intensive?
What is low-carbon concrete?
There is no globally agreed definition for low-carbon concrete. What is commonly perceived as a low carbon concrete in the construction industry, is a concrete mix that results in lower embodied carbon compared to an average concrete mix.
However, there is no agreed benchmark in most regions and no agreed percentage reduction of embodied carbon in order for the concrete mix to be classified as low-carbon. Local attempts at doing this include the Concrete Sustainability Council (Germany), Lavkarbonbetong standard (Norway) and the UK’s Low Carbon Concrete Code.
This results in the term being used in any case where concrete has lower embodied carbon than a typical Portland cement mix, even if the reduction is minimal and at times even nominal. In most cases, the reduction of embodied carbon will be the result of cement substitution with more traditional alternative binders like Fly Ash, Ground Granulated Blast Furnace Slag (GGBS), calcined clays and in some limited cases natural pozzolans, and with innovative new solutions. This list is not an exhaustive list, many other solutions exist as well.
The problem with most of the low-carbon concrete made today is that clinker (the key ingredient of cement) is substituted with secondary materials from fossil fuel-based processes. While this is a useful transition mechanism, it cannot scale as we decarbonize power generation and other industries.
Concrete is used in foundations, slabs and the structural frame of most buildings across the world. With the majority of concrete’s embodied carbon coming from the production of cement the key to reducing concrete’s embodied carbon is to reduce the total amount of cement used. This must be done via:
- Avoid overdesign of structural elements. This will reduce the amount of concrete and cement being used.
- Rationalisation of live loads consideration during design. Live loads are often overestimated. Load overestimation can be avoided by detailed structural design without affecting any future adaptability of the building.
- Design for material efficiency by optimising the span of the structural grid and incorporating more material efficient concrete elements like hollow core slabs, and composite decks.
- Avoid over specifying concrete’s compressive strength. Concrete mixes can be optimized for specific parts of the building; there’s no need to use standard strength throughout.
- Avoid over specifying concrete’s compressive strength in the early days after pouring (7, 14 and 28 days). This will allow the use of concrete with alternative binders that in most cases have longer curing times.
- The use of alternative binders like Fly-Ash, GGBS, calcined clays etc.
- The use of other innovative concrete solutions, where present, that are not necessarily related to cement reduction.
A key benefit of optimizing concrete and cement clinker quantity is that it saves capital costs.
Alternative binders to cement
- Fly Ash / Pulverized Fuel Ash
- Ground Granulated Blast Furnace Slag
- Calcined Clays
Fly Ash / Pulverized Fuel AshPulverised fuel ash (PFA), also known as fly ash, is a by-product of coal combustion in power plants. When coal is burned, it produces a fine, powdery ash that is carried away by the exhaust gases. This ash is collected and used as an alternative binder in concrete. PFA replaces typically around 30% of clinker but can be used at higher percentages as well. When added to concrete, PFA reacts with the cement hydration products. The product of this reaction results in denser and more durable concrete. Concrete with PFA like most other alternative binders will require longer curing times.
Ground Granulated Blast Furnace SlagGround Granulated Blast Furnace Slag (GGBS) is a by-product of steel production, specifically the blast furnace process, where iron ore is melted to produce iron. GGBS can be used as a partial replacement for clinker in concrete, typically replacing up to 50% of it but being able to reach much higher percentages as well. As with PFA, its main drawback is the longer curing time required by concrete made with GGBS binders.
Calcined claysCalcined clay is a type of pozzolan that is produced by heating certain types of clay minerals to high temperatures (around 700-900°C) in a process known as calcination. This process causes the clay minerals to undergo a chemical transformation, resulting in the formation of a highly reactive amorphous aluminosilicate material that can react with calcium hydroxide, a product of cement hydration, in the presence of water to form additional cementitious compounds. Clays suitable to be used for calcined clay have a high content of alumina and silica. One such type of clay is Kaolin, also known widely as China clay.
Other bindersOther alternative binders, albeit not used as extensively, include rice husk ash and gypsum. Rice husk ash is a by-product of rice production. When rice husks are removed from rice, they are burned. The ash resulting from this process is known as rice husk ash and has a high content of silica which allows it to produce additional cementitious compounds when reacting with carbon hydroxide which is a product of cement hydration. A key benefit of rice husk ash is that it is a renewable resource.
Carbon capture technologiesA significant cause of the carbon emissions of concrete is the calcinations process during the production of cement. Even if the main energy being used in the production and transportation of concrete were zero carbon, the calcination related emissions would remain the same. To address this, Heidelberg Materials is currently building the world’s first carbon capture and storage facility in a cement production plant in Brevik, Norway and planning to do the same in the Slite plant in Sweden.
Carbon Dioxide injectionSuch technologies aim to use captured CO2 by injecting it in concrete while still in liquid form. CO2 then reacts with cement and water to produce more cementitious compounds. Such technologies already exist commercially and can be applied to existing concrete plants. CarbonCure, a Canadian company, and Carbonaide, a Finnish company, are developing technologies that can be used in existing ready mix concrete and precast concrete respectively. CarbonBuilt has developed a similar technology for the production of ultra low carbon concrete blocks. The technology can be integrated in any existing concrete block plant and reduces the embodied carbon of the blocks by replacing the cement with another alternative material that reacts with injected CO2 during the curing process to form CaCO3 (limestone). The first commercial production of concrete blocks using this technology was started by Blair Block in Alabama, USA, in 2022.
BiotechnologyResearch is also being undertaken on how low carbon concrete can be achieved with the use of biotechnology. Prometheus Materials in the USA has developed a concrete mix that uses algae to replace Portland cement. Their solution has been used in pilot projects and efforts are being put towards the full commercialisation of the product. Biozeroc, a startup in the UK is a biomaterials company that produces low-carbon concrete using bacteria. Their process uses bacteria to bind aggregates and sand together into a material that performs as well as conventional concrete. This BioConcrete production process emits at least 85% less carbon, and has the potential to be carbon-negative once waste materials are incorporated into the bacterial feedstocks.
Plant based solutionsPlant based solutions include materials that in many cases are a mix of lime, sand, clay and plant fibres. One such material is hempcrete which is made of lime, sand and hemp fibres. Such materials can be used for cast in place elements, shotcrete and masonry units. Although these materials are bio-based and come with ultra low embodied carbon, they cannot substitute traditional concrete other than for small buildings and non-load bearing applications.
Get early design insights with Carbon Designer 3D
How could concrete become more circular?
The role of the specifier in low carbon concrete
The role of contractors in low carbon concrete
Comparing concrete mixes and how to model low carbon concrete in One Click LCA
- Industry average EPDs from manufacturer associations (e.g. NRMCA)
- One Click LCA generic datapoints for Portland cement mixes and concrete grades ranging from C12/15 (1700/2200 PSI) to C60/75(8700/10900 PSI)
- One Click LCA generic datapoints for concrete grades as above with cement substituted with PFA at a range from 10% to 50%.
- One Click LCA generic datapoints for concrete grades as above with cement substituted with GGBS at a range from 10% to 75%.
- Portland cement
- Ground Granulated Blast Furnace Slag
- Pulverised Fly Ash
- Silica Fume
- Standardised cement types like CEM I, CEM II, CEM III and CEM IV
- Virgin and recycled concrete aggregates at various densities
Find out more about how to create private datasets and private constructions with One Click LCA via these helpdesk articles.
How to compare different concrete mixesA quick and simple way to compare different concrete mixes using One Click LCA, is to add the datapoints of interest to the “compare data” feature. This will automatically generate a graph showing the carbon emissions per life cycle module for each of the compared mixes for the required functional unit. The feature is available for both generic datapoints and manufacturer specific EPDs and can be used for any material type.
Find out more about how to use the Advanced Material Comparision feature.
Sustainable concrete reinforcementConcrete, especially in buildings, will typically be used together with steel reinforcement. Reinforcement is necessary in order to allow concrete elements to carry tensile forces which otherwise would not be possible due to concrete’s low tensile strength. Depending on the region, the reinforcement rate and the recycled content of the steel reinforcement bars, reinforcement can be responsible for up to 50% of the reinforced concrete’s embodied carbon. (100% Portland cement mix with 60% recycled rebars and 200kg/m3 reinforcement rate). To reduce the impact of reinforcement in concrete, there are various alternative reinforcement types that can be used. None of them can be as versatile as the traditional steel reinforcement bars, however in many cases, using one of the following alternative reinforcement types could result in significant embodied carbon savings. The alternative reinforcements can be categorised into organic fibres like hemp fibres, steel fibres which are used widely in various applications like industrial floors, and other mineral fibres or bars made for example from glass and basalt. The following generic datapoints for alternative reinforcement can be found in the One Click LCA database in addition to the various EPDs developed by manufacturers.
- Bi-component polyester fibre, 100% recycled content
- Hemp fibres, straw and shives
- Basalt fibres
- Steel fibre for concrete reinforcement, 0% and 100% recycled content
- Glass fibre for concrete reinforcement
- Polypropylene fibre for concrete reinforcement, ranging 0% – 100% recycled content
- Flax fibre
- Jute fibre
- Kenaf fibre
- Basalt rebar for concrete reinforcement
How to find a lower carbon concrete mix in your regionWhen the time comes to specify the exact concrete manufacturer from where concrete will be procured – usually at detailed design stage or construction stage – how do you find lower impact concrete mixes and manufacturers? One Click LCA’s green material benchmark feature enables you to identify all plant specific mixes that have lower embodied carbon than the one you have already selected. The feature is available either directly from the material query through a material’s data card or via the results page where you can ask One Click LCA to give you a list of more sustainable alternatives to your currently chosen materials.
Find out more about green material benchmarks.
Who can supply low carbon concrete solutions?
- Mexico: Forzac Concretos
- California, USA: Graniterock
- Washington, USA: CalPortland
- Massachusetts, USA: Boston Sand & Gravel
- Canada: Lehigh Hanson
What is the future of low carbon concrete?
Low or lower carbon concrete is currently made available mostly by replacing cement with alternative binders like GGBS, PFA and silica fume. With the construction industry urgently needing to decarbonise as soon as possible, the demand for such alternative binders is continuously increasing and will increase more in the future. At the same time, the supply of some binders like Fly Ash which is a by-product of coal combustion is set to decline due to the reduced demand of the primary product (e.g. coal based electricity).
Concrete must be made available at even lower embodied carbon than typically achieved now with binders like GGBS and PFA and it must be produced with new innovative manufacturing processes and binders.
In its UK concrete and cement industry roadmap to beyond net zero, the UK Concrete Centre has identified a potential to reduce the embodied carbon of concrete by 39% by 2050 due to the decarbonisation of the electricity grid and transportation, lower carbon production of cement and other binders and the switch of the main fuel used in cement production to a renewable fuel. The remaining 61% reduction required for concrete to become a zero carbon material must come via carbon capture technologies which will address mostly the calcination related emissions.
Heidelberg Materials is already building the first Carbon Capture and Storage facility in a cement production plant in Norway and is planning to do the same in another one in Sweden by 2030. Other companies like CarbonCure and Carbonaide as mentioned above reduce the embodied carbon of concrete by using CO2 in the concrete mix itself while companies like Prometheus Materials and Biozeroc are looking into using biotechnology to eliminate the use of cement in concrete to allow reaching a zero or negative carbon building material similar to concrete.
Affordable EPDs with One Click LCA Concrete EPD Generator
Learn more about the One Click LCA Concrete EPD generator or watch the recording of our recent webinar on how to create fast concrete EPDs.
Consulting and Training Team LeaderMarios Tsikos is an LCA, BIM and sustainability expert with 10 years’ experience. He is now a consultant at One Click LCA, providing training and supporting customers to integrate LCA into their workflows.
About Ecodesign in Practice
Ecodesign in Practice is a series of sustainable construction design solutions that can be applied at scale. The solutions are also integrated as data sources in One Click LCA for Buildings and Carbon Designer 3D. We publish an article and associated solutions approximately every six weeks. We hope you enjoy reading and would love to hear your feedback.
Other articles in this series
Learn more about low-carbon materials with our EPD and LCA BootcampsConcrete, along with many other construction materials, will be covered in One Click LCA’s upcoming Construction LCA and EPD Bootcamps. These five-day programs provide you with the knowledge required to undertake a construction project LCA or prepare a construction product EPD respectively.
Table of contents
What is low-carbon concrete?
What is the future of low carbon concrete?
Affordable EPDs with One Click LCA Concrete EPD Generator