Jul 18, 2023
Why We Make Ordinary Portland Cement: Brimstone's Approach
We've reimagined how to produce the most widely used cement in the world—without the carbon emissions.
Ordinary portland cement (OPC), the key binder in concrete, has been the foundation of construction for over a century. Today, 95% of cement produced in the United States is OPC. It is trusted for virtually all construction, from skyscrapers, shopping malls, and hotels, to offices, schools, hospitals and residential homes, as well as for critical infrastructure such as bridges, tunnels, highways, and dams.
Concrete made with OPC uniquely combines strength, durability, and versatility. Structures made of concrete with OPC can withstand extreme temperatures, water and saltwater, and harsh chemical exposures, making OPC the go-to solution for a wide range of construction projects—qualities that will be increasingly important due to extreme and unpredictable weather patterns caused by climate change. Just as importantly, OPC’s long track record gives engineers and builders confidence in how OPC will perform over the life of a structure.
Historically, OPC has been made via two chemical processes that produce calcium oxide from raw rock, either from gypsum or from limestone. The gypsum-based approach, known as the Müller-Kühne process, generates hazardous sulfuric acid as a byproduct, making it impractical and non-scalable today.
The limestone method has long been the dominant process for manufacturing OPC. However, it has one serious drawback: Limestone contains carbon, which is released as carbon dioxide during manufacturing. The process emissions related to heating limestone are responsible for 60% of total cement production CO2 emissions, releasing nearly 1 ton of CO2 for every 1 ton of cement produced.
Cement production accounts for a staggering 7.5% of global CO2 emissions today. In fact, if the cement industry were a country, it would be the third-largest emitter in the world.
But Brimstone has successfully invented a third OPC manufacturing process: using carbon-free calcium silicate rock instead of limestone.
OPC produced through Brimstone’s process is chemically and physically identical to the cement used today. The key difference: Brimstone’s production process is carbon-negative across a range of energy profiles
An independent, accredited lab recently validated that Brimstone's cement met or exceeded ASTM C150, an industry-wide standard defining what constitutes OPC. For OPC to be used on construction projects in the United States, it nearly always meets the ASTM C150 standard. As the first ultra-low carbon, carbon-neutral, or carbon-negative cement to meet these standards, the ASTM certification affirms that Brimstone’s cement is the same as traditional OPC and can be used seamlessly on construction sites worldwide. And most importantly, Brimstone’s decarbonized cement provides a viable pathway to eliminate cement’s negative climate impact.
Over time, many other types of cement have been developed and marketed as alternatives to portland cement, including Calcium Aluminate Cement, Calcium Sulfoaluminate Cement, Magnesium Oxychloride Cement (ASTM C247), and Magnesium Phosphate Cement. In fact, in 1992, ASTM approved a performance standard, ASTM C1157, for hydraulic cements. This created a way for new types of cement to show they meet certain basic requirements.
These alternative cements produce concrete with different properties such as different setting times, expansive behavior, and altered strength development. So far, these materials have been used primarily for niche applications and have not gained broad traction in the market as a portland cement replacement. Together, they represent a small fraction of global consumption.
One motivation for developing alternative types of cement is lower production emissions compared to conventional portland cement. Brimstone’s cement not only provides a carbon-reduction solution, but also meets ASTM C150 standards—proving that it’s possible to produce OPC, minus the emissions.
OPC is the material that builders use, know, and trust. With Brimstone’s ASTM-certified, carbon-negative OPC production process, we can continue to build—while transforming one of the biggest climate problems into a climate solution.