Cement is ubiquitous in our lives yet inconspicuous, being used to construct roads, dams, basements, and various buildings. However, within these omnipresent grey slabs lies a climate threat.

Cement production accounts for over 7% of the global carbon dioxide emissions, surpassing industries such as aviation, shipping, and landfill.

For thousands of years, humans have been making cement in some form. The ancient Romans used volcanic ash, crushed limestone, and seawater (an early version of cement) to build iconic structures like aqueducts and the Pantheon.

The "modern version" of cement dates back to the early 19th century, which hardens and dries when mixed with water. It requires easily accessible, low-cost, and easy-to-produce materials. Today, cement is one of the most widely used materials on Earth, with an annual production of about 4 billion tons.

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Industrial-scale cement production poses a multifaceted climate challenge. Its manufacturing process is energy-intensive: the inside of a traditional cement kiln is hotter than the lava during a volcanic eruption.Reaching such temperatures typically requires the combustion of fossil fuels like coal. The transformation of crushed minerals into cement also requires a series of specific chemical reactions, which release carbon dioxide, the most common greenhouse gas in the atmosphere.

A potential solution to this climate disaster could be the use of technology from Sublime Systems. This startup, founded by two battery scientists from the Massachusetts Institute of Technology, is developing an entirely new method for cement production.

Instead of heating crushed rocks in a volcanic-like hot kiln, Sublime's technology uses electricity to place them in water, triggering a chemical reaction that forms the main component of cement.

Over the past few years, this startup has evolved from being able to produce a small piece of cement to establishing a pilot facility capable of producing about 100 tons of cement per year.

Although it is still small compared to traditional cement plants that can produce over a million tons per year, the pilot line has proven that electrochemistry can help address the challenges of cement production, one of the most important building materials in the world, taking an important first step.By the end of this century, Sublime plans to establish a complete production facility capable of manufacturing 10 million tons of materials annually. However, the construction and equipment costs for a traditional large-scale cement plant may exceed 1 billion U.S. dollars.

Competing with established industry players will require Sublime to expand rapidly while raising additional funds needed to support growth. The end of the era of low-interest rates makes it increasingly difficult for any business to accomplish this task, especially for enterprises producing bulk commodities such as cement.

In high-risk, low-profit industries such as construction, Sublime first needs to persuade builders to use its materials.

The cement industry emits 2.6 billion tons of carbon dioxide into the atmosphere each year. Addressing this issue requires tackling two different sources of cement greenhouse gas emissions: heat and chemistry (process).

Today, to manufacture cement, we typically grind a mixture containing limestone, sand, and clay and heat it in a kiln at temperatures up to 1500°C (slightly above 2700°F). The high temperatures trigger reactions that convert limestone into lime and combine it with the silica in sand and clay.These reactions are quite complex, but in most cases, the key end products are mixtures of compounds of silicon, calcium, and oxygen, which cause cement to harden into concrete after being mixed with water (and the addition of sand and gravel), becoming a solid building material.

By weight, humans use more concrete than any other material except water. Cement acts as the glue that binds the materials together, accounting for about 10% of its volume.

Approximately 40% of greenhouse gas emissions related to cement production come from fossil fuels that generate heat. This is a common issue across the entire heavy industry.

Rebecca Dell, the head of the industry group at the non-profit research organization ClimateWorks, said that due to the low cost of fossil fuels, they have become deeply entrenched in the production process.

However, lower-cost renewable energy is entering the power grid, opening the door for more industrial sectors to switch to electricity.Producing cement using electric kilns is feasible. Some major industry players, such as Cemex, are working to test this technology to reduce emissions from heat requirements. If these electric kilns are powered by renewable electricity, it could be a potential way to reduce the climate impact of cement.

However, this does not make up for other sources of emissions in the cement production process: about 60% of emissions do not come from heat but from the chemical reactions required to transform raw materials into building materials.

Most cement starts with limestone, a sedimentary rock containing calcium, oxygen, and carbon. In the cement kiln, limestone is transformed into lime through a series of reactions, a process that typically releases carbon dioxide into the atmosphere.

In terms of sheer volume, the emissions of carbon dioxide cannot be ignored. This means that complete decarbonization of the cement industry may require a more thorough transformation, which is where Sublime comes in.

Leah Ellis, co-founder and CEO of Sublime, said: "I think cement has not received the attention it deserves."She speaks with a slight Canadian accent, her words tumbling out quickly as if time is of the essence. Her eyes sparkle as she explains the complexities of cement chemistry.

Ellis did not initially set out to enter the building materials industry. After growing up in Canada, she completed her graduate studies under the guidance of renowned battery pioneer Jeff Dahn.

She then moved on to the Massachusetts Institute of Technology, where she collaborated with another key figure in the field of battery research and serial entrepreneur, Yet-Ming Chiang.

Yet-Ming Chiang has founded several energy storage companies, including A123 Systems, 24M, and Form Energy, and currently co-founded Sublime Systems with Ellis.

When Ellis first arrived at MIT, it was Yet-Ming Chiang who proposed a different idea for her research there. She recalls that he brought her into his office and then asked if she was already tired of batteries, which took her by surprise."I think this is a question with a trap," she said, "because he is a renowned battery scientist." But at that time, Jiang Yeming had an idea to use a tool from battery science to manufacture cement: electrochemistry.

Jiang Yeming suggested that instead of burning fossil fuels to heat the cement kiln, it would be better to find a way to use electricity to trigger the chemical reactions necessary for making cement.

They later discovered that a device called an electrolyzer might come in handy in this process. An electrolyzer is a device that uses electricity to initiate chemical reactions. They are commonly used to split water, producing hydrogen and oxygen.

However, electrolyzers can also work with other chemical reactions, such as producing acids and bases, which are key to the new cement production process.

By 2019, Ellis and her colleagues found a method that might realize Jiang Yeming's idea.They discovered that an electrolytic cell could be used to create a pH gradient within the cell, with the acidic end being dissolved limestone and the other end being slaked lime. Then, the lime could be combined with reactive silica, resulting in a compound that is the same as the compound formed by traditional cement (manufacturing).

After some subsequent technological development and industry analysis, the two decided to develop this research into a company led by Ellis. Jiang Yeming said: "It didn't take long for me to realize that this idea needed someone to make it happen."

Four years later, Sublime launched the operation of a pilot production line. This was a significant advancement compared to the early results at MIT.

There, Ellis and her laboratory partner produced enough material to make a mold. Sublime's Engineering Director, Mike Corbett, said that this production line was launched at the end of 2022, which is 20 times larger than any product line the company operated in the laboratory.

In a cavernous room at the headquarters of this startup, stainless steel boxes on the walls are arranged from left to right. The boxes on one side of the room contain crushed rock, and the boxes on the other side contain slaked lime, which is one of the main ingredients of Sublime cement.The results of various experiments and test runs are stored in nearby barrels, stacked on metal racks. When Corbett and a colleague opened a lid, the slaked lime inside was a white powder, somewhat clumped together, much like damp baking soda.

However, the contents of these barrels are not enough to build anything. At full capacity, the pilot line would need about a week to produce enough cement to fill a concrete truck. In the United States, an average single-family home requires three to four truckloads of cement to pour the foundation.

Currently, the startup is making material samples, with the aim of sending them to potential partners, testing the cement blocks, and most importantly, helping to design the next batch of manufacturing facilities.

These planned new facilities will be much larger and may be the final step in proving that Sublime's process can play a role in the cement industry.

Sublime is not the only player trying to make "gray glue green." Radhika Lalit, Director of Industrial Initiatives at the Climate Imperative Foundation, said that early efforts to reduce cement emissions focused mainly on efficiency, and she previously worked in the industrial group at the non-profit research institute, the Rocky Mountain Institute.For example, adding fillers known as supplementary cementitious materials, which can react with the active components in cement, helps to reduce total emissions without affecting the performance of the concrete.

Lalit points out that this strategy is only effective to a certain extent, as these fillers can reduce the strength and lifespan of the cement.

There are other methods to add materials to cement to reduce the climate impact. For instance, the Canadian company CarbonCure has developed technology to inject carbon dioxide into cement mixtures.

According to CarbonCure, the carbon dioxide gas can react and mineralize with the mixture, sequestering it from the atmosphere and increasing the material's strength. CarbonCure is collaborating with carbon removal companies such as Heirloom Carbon Technologies to demonstrate the potential for long-term storage of carbon dioxide using concrete.

However, methods such as reducing the total amount of materials used or adding auxiliary materials have limitations in reducing emissions; they cannot make unlimited efficiency adjustments to achieve zero emissions. Lalit says that many established companies in the cement industry are looking to add carbon capture and storage equipment to their existing facilities.Capturing carbon dioxide from industrial exhaust before it is released into the atmosphere can help facilities reduce emissions, making the entire industry cleaner without the need for a complete equipment overhaul.

Adding carbon capture technology to existing infrastructure may mean extending the service life of traditional equipment. This is an important benefit for recently built factories, as they typically have a lifespan of 30 to 50 years.

However, in heavy industry, carbon capture remains largely unproven. Lallit says that existing methods often fail to capture all emissions, and the few large-scale installations in place also face delays.

The Rocky Mountain Institute states that to achieve net-zero targets, the cement industry needs to add carbon capture facilities to 33 to 45 existing cement plants by 2030. The first industrial-scale facility for cement plants is scheduled to go online in 2024.

This could be costly. The cost of removing one metric ton of carbon dioxide by carbon capture systems could be as high as $120, Ellis said, which would double the final cost of cement at current prices.Cost is one of the reasons why Sublime and some other startups avoid carbon capture and are committed to using more radical methods to reduce the carbon footprint of cement.

Another of the most well-funded cement startups is Brimstone, headquartered in California, USA, which has a so-called negative carbon cement production process. Cody Finke, CEO of Brimstone, says this means the product ultimately absorbs more carbon dioxide from the atmosphere than it emits.

Its technology mainly works in two aspects. Finke said that, first of all, Brimstone does not use limestone, but other silicate minerals that do not contain carbon dioxide, so the company's cement (manufacturing) process has no emissions.

In addition, the waste of silicate is a magnesium-containing material, which acts like a sponge, absorbing carbon dioxide from the air and mineralizing it.

Brimstone still has emissions in manufacturing cement, which is largely related to the required heat. But Finke explained that they can be effectively offset by other processes, especially because the company plans to use electric kilns.This startup company claims that if these materials are powered by the average American power grid, the final removal of carbon dioxide from its materials is more than the carbon dioxide produced during the manufacturing process, with carbon emissions of about negative 130 kilograms per ton of cement.

Despite Brimstone's energy needs and emissions, it insists on the reason for this high-temperature process is that the chemical formula it uses to produce cement is dominant in today's industry.

Portland cement has existed since the early 19th century and is the most common type of cement in the world. It is known for its ability to produce predictable and strong concrete.

However, there is a problem: manufacturing it requires ultra-high temperatures because a key component of cement, alite (A mine), can only be formed at temperatures above 1250°C.

Initially, Sublime also planned to produce Portland cement. "For something low-cost like cement, we think you need to produce what the market generally uses," said Jiang Yeming.The requirement for temperature prompted Sublime to reconsider when it began mass production: "We are innovating around an invention that is 200 years old."

Therefore, the research team conducted investigations and found that there were other ways to form chemical bonds, making its concrete strong enough to rival Portland cement (concrete made from it).

Sublime's material adopts one of the alternative routes, using lime and active silica to react with water to form the final material, instead of alite.

The choice of the cement chemical process may seem like a small issue. But in a high-risk industry like the construction industry, it could be a key decision factor for a startup to win large contracts and partnerships, and it could also be a key decision factor for failure.

"I think people are understandably skeptical about new cement," Ellis said, "However, it is not entirely new cement either."Ellis insists that Sublime's material is as durable as Portland cement, and may even surpass it. However, Lalit from Climate Imperative suggests that developers might hesitate, at least initially, as they decide whether to abandon a material they are already very familiar with.

One of the main challenges Sublime faces is producing the material on a scale required for large construction projects. Modern cement facilities can produce over a million tons of cement per year, while Sublime's pilot project has an annual capacity of only about 100 tons. Ellis says this is essentially a "cement factory for ants."

Sublime is looking to rapidly scale up. The next phase for the startup is to build a demonstration commercial facility that can produce tens of thousands of tons of material per year, which is expected to come online in early 2026. Ellis says, "At this scale, the cement world will see its existence."

After that, there will be a full-scale commercial plant with an annual production capacity of millions of tons, meeting typical industry demands. The company is still researching where to build it, but it hopes to have it operational around 2028.

The founding duo of Sublime is well aware of the challenges ahead. Ellis says, "A cement startup might be one of the most difficult companies you can imagine."It is not only technically challenging but also requires a substantial amount of funding. Its scale is enormous, and it is not sexy... everyone uses and possesses cement, but they don't see it."

However, addressing this "invisible problem" could change our world. Cement supports our society, and attempting to change it is crucial for a cleaner construction industry, despite facing immense challenges.