Cement: The foundation of industrialized societies

Posted: September 24, 2024

Take a stroll through any city on Earth, and you’ll be hard-pressed to find a neighborhood untouched by concrete. Most vital infrastructure and shelter – roads, bridges, buildings – is made of concrete, making it the most widely used human-made material. Because concrete is so durable, versatile, and relatively cheap to produce, its status as the world’s most popular construction material remains unchallenged.

Concrete will likely constitute the cities of the future, but its use dates back thousands of years. Ancient Romans were long credited for discovering cement, which enabled their architectural revolution. However, recent archaeological studies of a royal structure commissioned by Alexander the Great have revealed that ancient Macedonians used cement at least three centuries before the Romans. Nevertheless, the Romans refined the recipe and built extraordinarily robust structures. Today, the Pantheon and the Colosseum, both nearly two thousand years old, stand strong as enduring testaments to Roman engineering prowess and concrete’s remarkable durability.

Cement production’s sustainability challenges

Concrete, not to be confused with its key ingredient — cement — is a composite made from aggregates, water, and the binding agent cement. Cement itself is produced from limestone and silica sources, fired at extremely high temperatures to create a powder. When mixed with water, this powder undergoes a chemical reaction called hydration. This process creates new, tightly interlocked compounds from the silicates, which harden over time, giving concrete its remarkable strength and longevity.

While concrete may have proven its durability over millennia, the industry faces challenges in making the production process more sustainable. That’s because you can’t make concrete without cement, and cement generates a high amount of CO2 emissions through a chemical process integral to its production. Indeed, cement production is one of the leading contributors to global carbon emissions.  With approximately 30 billion tons of cement produced annually, around 2.3 billion tons of carbon are emitted — accounting for roughly 8% of carbon emissions.

Cement production is only expected to increase in the coming decades, with emerging economies continuing to urbanize and therefore requiring more and more concrete. Despite well-known concerns about cement’s environmental footprint, a more sustainable alternative is unlikely to replace it soon. This is due not only to concrete’s uniquely useful properties, but also because limestone and other key cement ingredients are widely available across the globe. In fact, cement production is driven almost entirely by domestic demand, with only 2.6% of production traded internationally — compared to around 25% for steel. Cement production as a highly localized industry suggests that the sector’s capacity to decarbonize will not be heavily influenced by trade-related measures like tariffs. Instead, hopes for a greener cement sector are pinned primarily upon technological innovation.

How to decarbonize cement production

So what makes cement production such a carbon-intensive industry, and what can be done about it? The major challenge results from a process inherent to its production. Several mitigation strategies already exist, but the current technologies available can only contribute to 30% of the carbon reductions required to keep global climate goals.

About 60% of cement production’s carbon emissions come from calcination, the chemical reaction that results when limestone is exposed to high temperatures, creating a stony residue called clinker. These emissions are challenging to mitigate due to clinker’s central role in cement formulations. Lower-emitting substitutions for clinker, like fly ash, are promising options, though they are less widely available and have not yet been tested extensively at scale.

While clinker production is the primary emissions culprit, the remaining 40% of cement’s carbon footprint comes from the energy required to fire kilns in cement plants. Achieving the extremely high temperatures necessary for production currently relies on burning fossil fuels. Some researchers suggest using waste materials as an alternative fuel source, which could help reduce emissions. Electrification of kilns is another potential solution, but it remains technically and economically unfeasible at present.

The cement sector’s current best hope for approaching climate goals is the rapid and large-scale adoption of carbon capture and storage (CCS). CCS works by capturing carbon dioxide emissions produced during cement production and storing them underground or repurposing them in other industries. Companies like Solidia Technologies and CarbonCure are already leading the way by developing cement and concrete that not only incorporate CO2 during production but also sequester it, effectively locking it away. However, critics argue that CCS is expensive and energy-intensive, and that the need for it far exceeds capacity.

Cement’s hard-to-abate emissions present an ongoing challenge to the global community.  But the encouraging news is that because concrete is so widely used, even modest advancements in reducing its emissions can have a significant effect on our global carbon levels. On top of that, concrete has a leading role to play in paving the way to a greener future. Its unique properties make it ideal for constructing wind turbines, hydro-electric dams, public transportation infrastructure, and other cornerstones of sustainable development.