Could construction materials hold the key to climate change?

As the world comes to terms with the escalating effects of climate change, innovative solutions to mitigate carbon dioxide (CO₂) emissions have become more critical than ever. One of the most exciting developments is the potential to store billions of tons of CO₂ in newly manufactured construction materials such as concrete, cement and aggregates. This technology not only offers a sustainable way to utilise CO₂, but also has the potential to totally revolutionise the construction industry - to a point where construction materials could literally hold the key to climate change - writes John Ridgeway.

Concrete, one of the most widely used materials in the world, has emerged as a prime candidate for CO₂ sequestration. Companies like CarbonCure Technologies in North America have already pioneered methods to inject CO₂ into fresh concrete during mixing. This process traps the gas permanently and also strengthens the material, making it a win-win for sustainability and durability.

CO₂ gas is captured from industrial processes, purified and injected into the concrete mix. The CO₂ reacts chemically with calcium ions in the cement to form calcium carbonate. This mineral is stable and remains locked in the concrete for its entire lifespan. So effective is this process that CarbonCure claims that their technology can reduce the carbon footprint of concrete by 5% to 15%, depending on the specific application.

Another area of progress is the development of artificial aggregates made using CO₂. Companies like Blue Planet in the US have created synthetic limestone by combining CO₂ with calcium-rich industrial waste. These aggregates can be used in construction, replacing natural aggregates that require quarrying and transportation.

By reusing industrial waste and sequestering CO₂, this method addresses two environmental challenges simultaneously. While still in its early stages, synthetic aggregates have already been used in pilot projects, demonstrating their feasibility.

Traditional Portland cement production is responsible for approximately 8% of all global CO₂ emissions and as such is a major producer of green house gas. However, innovative alternatives, such as those developed by Solidia Technologies, another US company, use a different chemical process that reduces emissions by up to 70%. These cements can also absorb CO₂ during curing, further offsetting emissions.

Solidia’s process replaces the calcium-based raw materials with silica-based ones, which release less CO₂ during production. Early tests show that carbon-negative cements meet or exceed the performance standards of traditional cement, making them suitable for widespread use.

Pilot projects

Numerous pilot projects around the world have demonstrated the practical application of these technologies. For example, CarbonCure’s technology has been used in the construction of buildings, roads and other infrastructure projects across North America. Universities and research institutions have also partnered with industry players to explore novel ways of incorporating CO₂ into materials, pushing the boundaries of what’s possible.

However, a real understanding of the science is crucial to appreciating the potential of this technology. If we take a closer look, we can see that when CO₂ is introduced into concrete, it reacts with calcium hydroxide to form calcium carbonate. This reaction not only sequesters CO₂ but also enhances the strength and durability of the concrete. In artificial aggregates, CO₂ reacts with calcium or magnesium compounds to form stable carbonates. This process mimics natural geological processes, but occurs much faster.

Studies suggest that the construction industry could sequester billions of tons of CO₂ annually by scaling these technologies. For example, concrete alone has the theoretical capacity to store over 1 gigaton of CO₂ each year, a significant portion of global emissions.

Life cycle assessments (LCA) of carbon-sequestered materials, also show significant reductions in overall carbon footprints compared to traditional materials. These assessments consider factors like production emissions, transportation and end-of-life scenarios.

While achievements to date are promising, the potential for further innovation and scalability is immense. The application of CO₂ sequestration, for example, could extend beyond concrete to other construction materials such as bricks, asphalt and plasterboard. Research is already underway to explore these possibilities.

Integration with renewable energy

However, capturing and utilising CO₂ is energy-intensive, so it would make sense to integrate these processes with renewable energy sources, such as solar or wind, which could make the technology more sustainable and economically viable.

The efficiency of capturing CO₂ from industrial emissions is also a critical factor. Advances in carbon capture technologies, such as direct air capture (DAC), could provide a more reliable and scalable source of CO₂ for construction applications.

Furthermore, governments have a significant role to play in accelerating the adoption of carbon-sequestering construction materials. Policies such as carbon pricing, tax credits and subsidies for sustainable building practices could drive industry-wide change.

That said, scaling these technologies to a global level requires collaboration across industries and borders. Developing countries, in particular, could benefit from affordable and sustainable construction materials as they expand their infrastructure.

Incorporating CO₂ sequestration into a circular economy model could further enhance its impact. For instance, using industrial waste as a raw material for synthetic aggregates aligns with the principles of waste minimisation and resource efficiency.

Despite its promise, this technology faces several challenges that must be addressed to achieve its full potential. The upfront costs of implementing carbon sequestration technologies can be high, particularly for smaller manufacturers. The processes for capturing and injecting CO₂ also require energy and ensuring this energy comes from renewable sources is essential to maintain sustainability.

This means uniform standards will be needed to ensure the quality and safety of carbon-sequestered materials, if they are to gain public and industry trust. Educating stakeholders about the benefits and feasibility of these materials is also crucial for widespread adoption.

In spite of this, the idea of storing billions of tons of CO₂ in construction materials is more than a futuristic vision - it is a tangible solution that is already making an impact. From carbon-infused concrete to artificial aggregates and carbon-negative cements, the progress achieved so far demonstrates the feasibility of this approach.

However, the journey is far from over. By addressing challenges, fostering innovation and scaling these technologies globally, we can unlock their full potential and move closer to a carbon-neutral future.