Big Concrete Problem

Let us consider a moderately-sized skyscraper, standing at approximately 100 meters and comprising 30 stories. It is highly probable that a structure of this magnitude was constructed using concrete, a material that incorporates cement. In this instance, the quantity of cement utilized would have amounted to roughly 6,000 tons, resulting in the emission of approximately 4,600 metric tons of carbon into the atmosphere during the manufacturing process. This is equivalent to the emissions generated by driving a car for a distance of 12 million miles. When extrapolated to encompass all the buildings worldwide, this calculation fails to fully encapsulate the carbon footprint of cement.

Consider the pedestrian walkways upon which we traverse, as well as the thoroughfares upon which we operate our vehicles. Additionally, a significant portion of our energy infrastructure, including dams and power plants, contribute to the production of cement. This particular industry is responsible for a staggering 8% of all global carbon emissions, surpassing the combined emissions of both the aviation and shipping industries.

Currently, the majority of emissions can be attributed to the rapid development of China. In a mere two-year span, China's cement production surpassed that of the United States throughout the entirety of the 20th century. As other developing nations construct towering cities and infrastructure, cement usage will continue to rise. In order to achieve a net zero emissions status within the next few decades, it is imperative that we devise methods for constructing buildings without contributing to emissions. Although this will prove to be a challenging feat, it is indeed possible.

In the majority of conventional cement plants that are presently operational in various regions across the globe, a rotating tube, a kiln, and a preheater constitute the essential components where all emissions related to cement production occur. Approximately 40% of the emissions are attributed to the combustion of fuel to heat the kiln, which can reach temperatures of up to 1450 degrees Celsius in proximity to the heat source. The preheating tower is the designated location where limestone, clays, and other additives are introduced. At a temperature of 850 degrees Celsius, the limestone releases its stored carbon dioxide, which accounts for the remaining 60% of emissions.

The primary inquiry regarding the decarbonization of cement pertains to the possibility of reducing the overall usage of concrete. It is a common practice to incorporate an excess of 2 to 3 times the required amount of concrete in design, as architects and structural engineers tend to rely heavily on its usage. This approach is often deemed financially viable, as it enhances the reliability of the structure and reduces the likelihood of legal repercussions resulting from accidents. Concrete is particularly valuable in construction due to its compressive strength, which enables it to withstand significant weight. Therefore, it is challenging to substitute its use in critical areas such as foundations and columns. However, in other areas, it is advisable to minimize its usage.

A new Parliament building has been constructed in Scotland, which has evidently been designed with a focus on reducing greenhouse gas emissions. The use of concrete has been limited to only where it is necessary, while steel has also been used sparingly. Additionally, laminated wood has been utilized for the roof and other non-load bearing structural components. This carbon-conscious approach to design has the potential to significantly reduce the emissions associated with cement production. However, it is not currently feasible to completely replace concrete in the short term. Nevertheless, reducing the amount of excess concrete used in high-rise construction can result in a reduction of emissions by approximately 26%, according to one analysis. Further efforts will be required, and the next step should be to address the production process of cement.

Examining the portion of emissions that contribute to the firing of the kiln, which accounts for 40% of total emissions, is a logical starting point. Typically, coal, petroleum coke, or natural gas are utilized by cement plants to heat the kiln to a temperature of 1450 degrees Celsius. While it is possible to electrify this process, achieving such high temperatures with electric heat is a formidable challenge, although some emerging companies, such as the Finnish firm mentioned, are attempting to do so. In the meantime, cement plants have begun to utilize alternative fuels for combustion. The high temperatures involved make cement plants an ideal location for the incineration of industrial waste, refuse, or used tires. The limestone present in the kiln effectively removes any harmful substances produced, preventing their release into the atmosphere. Switching to alternative fuels can reduce emissions by approximately 7%, but there is still much progress to be made. Another significant source of emissions in cement production is the chemical process, specifically the carbon released from heated limestone. This carbon, once it has passed through the kiln, becomes clinker, the primary binding agent in cement. Cement is responsible for binding together the rocks, sand, and water in concrete, and while it accounts for only 10% of concrete, it is responsible for the majority of its emissions.

One potential approach is to identify a replacement for clinker. Various startups have been engaged in a competition to create an innovative form of eco-friendly cement that eliminates the need for clinker. However, to date, no alternative has been as widely available or economically feasible as the traditional limestone-based material. Furthermore, modifying concrete compositions requires extensive periods of time and rigorous safety assessments, which is entirely justified.

The recent events in Turkey have brought to light the issue of substandard cement usage and building practices. In North America, safety standards dictate that clinker accounts for approximately 90% of cement production. However, it is worth noting that North America's safety standards are considered overly cautious when compared to the rest of the world. The global average clinker-to-cement ratio in 2020 was approximately 72%, which is made possible by the use of clinker-like substitutes. Further reductions in the clinker ratio are possible, and experts have highlighted a new cement mixture that can safely reduce the clinker ratio to 50% by supplementing it with more clay and unprocessed limestone. This technology meets existing building codes and can reduce emissions from the cement and concrete industry by half. However, until a scalable, zero-emission cement is developed, any clinker production will inevitably result in process emissions. Therefore, the cement industry must use carbon capture and storage to achieve decarbonization. This involves capturing the carbon emitted during heat and chemical processes and storing it deep underground in a geologic deposit.

A Norwegian cement company is currently conducting a pilot project for one of the world's first cement plants designed to capture carbon. The captured carbon will be stored in oil and gas deposits beneath the North Sea. Additionally, some emerging companies are exploring the possibility of injecting stored carbon back into cement and concrete during production, taking advantage of the natural ability of rock to reabsorb carbon. In the future, it is possible that our built environment may become a carbon sink, a concept not typically associated with large concrete cities, buildings, and roads. Achieving net zero emissions in the building sector by 2050 is the current goal, which requires immediate and aggressive action, particularly in China, the world's largest producer.

However, experts have conveyed some positive news regarding the matter. In the United States, the average age of a cement plant is approximately 34 to 35 years, whereas in China, it is only 15 years. This indicates that many of their plants are more energy efficient than those in the US. China employs less clinker in their cement production than the global average and has initiated at least one carbon capture project. Nevertheless, there is still a considerable distance to cover. In the previous year, China postponed their peak building emissions deadline from 2025 to 2030. The most straightforward changes to implement would be in the design of concrete and cement processes, but carbon capture and storage are still in their nascent stages. Furthermore, the expenses involved in these modifications are substantial. The cost of cement or concrete is a minor fraction of the overall project cost. Therefore, it is relatively simple and cost-effective for a government agency to commit to paying a slightly higher price for the material to absorb the green premium. The US Inflation Reduction Act is aiding in the creation of a market for carbon capture and storage by increasing tax credits to $85 per metric ton of carbon stored.

For an extended period, weighty industries such as cement have appeared to be insurmountable climate predicaments. However, presently, we possess the knowledge to rectify these issues, and it is imperative that we make an effort to do so. It is unlikely that wood can supplant concrete in all of the world's edifices. Furthermore, in order to expand the use of wood, we would need to triple the amount of timber harvested, which would result in its own environmental challenges. Nevertheless, our significant concrete predicament necessitates a multitude of solutions, and incorporating wood whenever feasible is unquestionably one of them.