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The Transition Towards ‘Green’ Concrete in Construction


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The concrete industry is one of the top emitters of greenhouse gases and is responsible for approximately 7% of the global CO2 emissions. For comparison, the aviation sector accounts for less than 3% of the global CO2 emissions. Concrete is the second most consumed substance on earth after water and is a critical material used for buildings and infrastructure. Assuming current practice, the global demand for concrete is predicted to grow by as much as 38% in 2050, rising to approximately 20 billion m3 in volume from 14 billion m3 in 2020. Considering the environmental footprint of traditional concrete, there is an increasing interest in the industry to find more sustainable “green” concrete solutions. As of 2020, the Global Cement and Concrete Association (GCCA) have brought together 40 of the world’s leading cement and concrete companies to announce their commitment to producing Net Zero Concrete by 2050.  

GCCA’s path towards Net Zero Concrete

 

What is concrete and why does it have high CO2 footprint? 

Concrete is a composite material consisting of cement, aggregates (such as gravel and sand) and water. A commonly used traditional cement is known as Portland cement and the production process (see image below) includes a calcination step where raw materials, consisting mostly of limestone and clay, are heated in kilns at very high temperatures of around 1450°C. Not only it is a highly energy-intensive process, the chemical reaction during calcination is also a main contributor of CO2 emissions. When limestone, a rock made of calcium carbonate is heated, this calcium carbonate breaks down into calcium oxide and carbon dioxide, thus releasing CO2 into the atmosphere. Around 50-60% of the CO2 emissions come from the calcination process itself while the other 40% of CO2 emissions come from the combustion of fossil fuels used to heat the kilns.  

Process for making traditional Portland cement and the associated CO2 emissions (source: Hoffmann)

 

Innovations on low-carbon concrete aimed at slashing CO2 footprint  

There are several technologies that are being developed to decarbonise CO2 arising from the manufacturing of concrete. One such innovation is the Brimstone process that enables the production of cement without the need for carbon-heavy limestone. Brimstone is a 35-person California-based start-up and their method starts with carbon-free calcium silicate rocks where calcium oxide is chemically extracted from the abundant calcium silicate rocks without releasing any CO2. In addition, their process results in Magnesium as a byproduct which can absorb CO2 from the atmosphere. In July 2023, Brimstone announced that they have received third-party certification validating that their cement is structurally and chemically the same as Portland cement, thus meeting the ASTM C150 standards for ordinary Portland cement. The company claimed to be the first carbon-neutral or carbon-negative cement to meet the critical industry requirement, unlocking the potential towards decarbonising the concrete sector. Brimstone is currently working on its first pilot production plant in Nevada, but their technology is still years away from commercialisation.  

CarbonBuilt is another California-based start-up that have tackled the carbon intensive concrete sector via 2 approaches, i.e. (i) replacing Portland cement with their proprietary, low-carbon alternative cement material and (ii) piping CO2 into curing chamber for strengthening concrete blocks instead of using conventional steam generated by natural gas. To make concrete blocks, CarbonBuilt’s low-cost cement material is mixed with water and aggregates and then pressed into shape. These concrete blocks are hardened by chemically reacting with piped CO2 and not only does this process enable the strengthening of the concrete blocks, it also permanently stores the CO2 in solid form. CarbonBuilt’s method is said to reduce overall CO2 emissions from concrete-making by 70-100%. In May 2023, the company announced that they have begun commercial production of its concrete technology in Alabama with its partner, Blair Block where the first concrete blocks off the production line would be used by masonry contractor, C&C Masonry to be integrated in several municipal projects across the state, including a firehouse.  

Besides creating novel cement technologies, companies such as Coolbrook and Synhelion are looking at replacing the combustion of fossil fuels used for heating kilns with cleaner energy. Coolbrook is a Finnish-Dutch company offering its patented RotoDynamic Technology that is capable of heating kilns via electrification. Its RotoDynamic Heater (RDH) is claimed to be the only electric process heating technology capable of reaching 1700°C and is said to have potential to cut CO2 emissions by 30%. Coolbrook is currently working with industrial partners such as ABB, Cemex and UltraTech to explore and test its RotoDynamic Technology for the electrification of cement heating process and expected their technology to be ready for commercial scale use in 2025.  

On the other hand, Synhelion is developing a concentrated solar radiation technology that can be used for powering kilns to temperatures above 1500°C, without the need for fossil fuels. Based in Switzerland, Synhelion was spun-out from ETH Zurich in 2016 and has been working with Cemex since 2019 to decarbonise cement production using their solar technology. At end of 2021, both Synhelion and Cemex have set up small pilot production batch unit and successfully produced clinker using Synhelion’s solar technology. Clinker is a material produced in the cement production kilning stage which is then further processed to make concrete. Both parties are now working towards building an industrial-scale pilot cement plant and in February 2023, they were awarded US$ 3.2 million by the United States Department of Energy to scale the technology further. 

Another strategy for creating a zero–carbon concrete product is by removing both the calcination step (that produces 60% of CO2 emissions) and the use of fossil fuels for heating kilns (which contributes to 40% of CO2 emissions). Sublime Systems is one company that is doing so with its electrochemical process. Spun-out from MIT in 2020, Sublime Systems is developing a process where water-splitting electrolyser is used to produce acid and base. Carbon-free rocks can be dissolved in the acid to extract calcium which is then reacted with the base to create calcium hydroxide, or lime. This lime can then be blended with silica to produce the “Sublime cement”. The whole process takes place at ambient temperatures and requires neither heat nor carbon-heavy limestones, therefore producing zero carbon emissions. In September 2023, Sublime cement obtained the ASTM C1157 designation, allowing it to be used compliantly under major United States and international building codes, unlocking a path for Sublime cement to replace the traditional Portland cement at scale. In January 2024, Sublime Systems were awarded US$6.7 million by the United States Department of Energy to advance their electrolyser technology. The company is currently constructing its pilot plant in Massachusetts, USA and expect to begin operation in 2026.  

Sublime Systems’ electrochemical approach vs. traditional Portland cement making process

 

Adoption of new sustainable concrete solutions are still too slow 

Eco-friendly concrete technologies are not new and there are many exciting new formulations for low-carbon concrete that have been developed throughout the years. However, technology developers are still faced with the challenge of convincing regulators, standards-setters, and contractors that these new cement and concrete technologies meet the specifications needed for construction. From the insurance industry perspective, there are additional risk factors with the use of new materials due to the lack of historical data demonstrating how these new materials would perform in practice when exposed to the environment over time. Hence, insurers have been hesitant to provide cover. This is made more challenging with reinforced autoclaved aerated concrete (RAAC) concrete recently found to be at risk of sudden collapse in hundreds of schools in the UK. RAAC, a material developed in Sweden during the 1920s as an alternative to traditional concrete mixes, is made from a combination of sand, cement, lime, and water and then aerated to create a highly porous and lightweight concrete. Not only is RAAC cheaper due to the use of less cement because of the air bubbles, it also speeds up construction projects as it removed the need for conventional on-site concrete processes such as pouring wet concrete and leaving it to cure for weeks. However, no one could have foreseen the shortcomings that RAAC faces currently, and this would inevitably have an impact on the future adoption of low-carbon concrete substitutes.  

That said, the GCCA aims to reach Net Zero Concrete by 2050, meaning radical approaches would be required to meet the goal. Replacing the well-established Portland cement and the conventional concrete manufacturing process would take time but it is believed that there will be considerable push in the next few years to get more low-carbon concrete technologies out of the lab and into the market. The examples of low-carbon concrete innovation discussed earlier are just a very small selection of technologies that are being developed currently.  

As an Open Innovation consultancy company, Strategic Allies has extensive experience in the global search for innovative technologies, solutions, products, strategic alliances and other new business generating opportunities across all sectors. If you’d like to find out more about how we can help you to explore and exploit new technologies and/or offer opportunities to differentiate your offerings, please contact John Allies at john@strategicallies.co.uk 

 

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