Decarbonizing Cement

Imagine a modest-sized skyscraper, standing tall at 100 meters and 30 stories. It was likely constructed with concrete, which is responsible for a significant carbon footprint. In fact, a building like this, weighing approximately 6,000 tons, emits around 4,600 metric tons of carbon during the cement production process. To put it into perspective, that's equivalent to driving a car for 12 million miles. Now, multiply that by all the buildings worldwide, and you begin to grasp the scale of cement's carbon emissions.

Cement production is a major contributor to global carbon emissions, surpassing even the aviation and shipping industries combined. This industry accounts for approximately 8% of global carbon emissions, primarily driven by China's rapid development. In just two years, China produced more cement than the United States did throughout the entire 20th century. As other developing countries continue urbanization and infrastructure development, cement consumption is expected to increase further.

If we aim to achieve net-zero emissions in the coming decades, we must find ways to construct buildings without emissions. While this is undoubtedly a challenging task, it is not impossible. Let's take a closer look at the cement production process and explore potential solutions.

A typical cement plant consists of a rotating kiln and a preheater tower. Around 40% of cement emissions are a result of burning fuel to heat the kiln, which reaches temperatures of approximately 1450 degrees Celsius. The remaining 60% of emissions come from the chemical process occurring in the preheating tower, where limestone releases carbon dioxide.

One approach to decarbonizing cement is to reduce the overall use of concrete. Architects and structural engineers often incorporate excess concrete into designs for reliability and safety reasons. However, minimizing concrete usage where possible can already result in a 26% reduction in emissions. Carbon-conscious design practices, as seen in the new Parliament building in Scotland, emphasize using concrete and steel only where necessary, while incorporating alternative materials.

To address the emissions from kiln heating, some startups are exploring the possibility of electric heat, although achieving the required high temperatures remains a challenge. In the interim, cement plants have started burning alternative fuels such as industrial waste, trash, or used tires. By switching to alternative fuels, emissions can be reduced by approximately 7%.

The chemical process involved in cement production, particularly the formation of clinker, is responsible for the majority of emissions. Clinker is a binding ingredient in cement and contributes significantly to its emissions. Startups are racing to develop green cement alternatives that avoid clinker entirely. However, finding an abundant and commercially viable substitute has proven challenging. Adjusting concrete formulas and using clinker-like substitutes have shown promise in reducing emissions.

To achieve substantial decarbonization, carbon capture and storage (CCS) will be essential for the cement industry. This process involves capturing carbon emitted during cement production and storing it underground in geologic deposits. Some cement plants, like the one in Norway, are piloting CCS initiatives by storing captured carbon in oil and gas deposits under the North Sea. Other companies are exploring injecting stored carbon back into cement and concrete during production, leveraging the natural carbon-absorbing properties of rocks.

While these measures can significantly reduce emissions, a scalable, zero-emission cement solution is still needed. Until then, any clinker production will inevitably result in process emissions. Therefore, the integration of carbon capture and storage technologies becomes crucial.

To expedite the decarbonization process, it is essential to start now and act aggressively, particularly in countries like China, which has a significant cement industry. China has already made progress in reducing clinker usage and has projects focused on carbon capture. However, significant efforts are still required, and the transition will be costly.

Addressing the challenges associated with cement emissions is a critical step in tackling climate change. By implementing sustainable construction practices, increasing research and development efforts, and promoting carbon capture and storage technologies, we can make significant strides toward decarbonizing the cement and concrete industry.

While there are no easy solutions, the urgency to combat climate change requires us to explore and adopt innovative approaches. Together, we can create a future where our built environment not only reduces emissions but also becomes a carbon sink. It's time to embrace the necessary changes and build a sustainable and greener world.