Paving the way for sustainable cement

Cement, a manufactured powder that holds concrete together, is the most widely used building material on Earth. It’s also one of the most polluting: Cement production accounts for nearly 8% of global greenhouse gas emissions.

Stanford geophysicist Tiziana Vanorio began researching this challenge 10 years ago after discovering rocks with unusual properties beneath her childhood home in Pozzuoli, Italy, a volcanic region where heat, pressure, and water drive intense chemical reactions underground. The rocks originated from volcanic ash, a so-called “pozzolan” for its cement-like ability to bind materials under reactive conditions. The formations intrigued Vanorio because they could withstand extreme warping before fracturing and had a composition similar to that of Roman-era concrete, the material underpinning enduring structures like the Pantheon.

Vanorio, an associate professor of Earth and planetary sciences at the Stanford Doerr School of Sustainability, sought to emulate the rocks’ properties in a new, engineered formula for modern cement. 

To make modern cement, industrial plants heat crushed limestone, which is primarily made up of calcium carbonate, in giant kilns. This step breaks limestone down into lime and carbon dioxide. At even higher temperatures, lime combines with other oxides to form a new solid material called clinker, the main active ingredient of cement. 

The chemical conversion of limestone to clinker accounts for nearly two-thirds of cement’s overall carbon dioxide emissions. The kilns, often powered by fossil fuels, account for the remaining emissions. Beyond its carbon footprint, the process is inefficient: Heating limestone converts about half of its mass into lime, and the other half into carbon dioxide, representing a significant share of rock that’s quarried and hauled but never makes it into the final product. 

In 2021, Vanorio identified a substantial limestone substitute that could significantly reduce carbon dioxide emissions when heated in the kiln. She chose a type of igneous rock that is not only abundant but also essentially carbon-free: Volcanic processes responsible for its formation already cooked off the carbon. When heated, these rocks emit very little, if any, carbon dioxide, instead yielding an engineered pozzolan rich in chemical activators that together function as lime, the key material for clinker.

Vanorio named her low-carbon cement recipe Phlego. 

Working with postdoctoral scholar Chengyao Liang, she engineered it to meet industry standards and mimic the fibrous microstructures of naturally cemented rocks, like those beneath Pozzuoli. Now, she’s working to make the scientific breakthrough commercially viable. 

In 2025, Vanorio received a grant from the Stanford Sustainability Accelerator, based in the Doerr School of Sustainability, that would help her and her team bring Phlego to market. Through Accelerator events and programming, she connected with representatives from global cement companies.

“I gathered a lot of information at the Accelerator events that helped me understand cement from a business perspective,” said Vanorio. “Decarbonizing cement isn’t just a low-carbon materials challenge. It’s really a risk allocation challenge. This was a pivotal moment for me.” 

Cement producers operate on razor-thin margins. To keep up with demand, kilns operate continuously to produce clinker. New manufacturing approaches that make production more sustainable have little room for additional costs.

Some cement companies have made manufacturing adjustments by substituting clinker with byproducts from industrial processes, such as coal combustion or metal refining, or with naturally occurring materials, such as volcanic ash. These partial substitutes, referred to as supplementary cementitious materials (SCMs) across the industry, reduce clinker content. As a result, less carbon dioxide is emitted, helping decarbonize manufacturing while maintaining cement’s overall strength and, in some cases, enhancing it over the long term.

However, SCMs are becoming increasingly scarce. Fly ash from coal combustion is declining as coal-fired plants phase out, and volcanic ash can only be sourced from certain regions. What’s available can also vary widely in composition, increasing the need for quality control. 

“Addressing the availability and consistency of supplementary cementitious materials will be critical for minimizing supply chain risks associated with producing low-carbon cement,” says Vanorio.

The market for SCMs is projected to expand at an average annual rate of 8% over the next decade as demand grows and supply dwindles. Engineered pozzolans, such as Phlego, could serve as a reliable alternative, helping validate and scale the adoption of low-carbon cement blends.

With Accelerator support, Vanorio has purchased a kiln and is expanding her team, working with research engineer Rotana Hay to optimize Phlego’s composition and performance as an SCM. She is also seeking an entrepreneur with experience in the cement sector.

Vanorio originally envisioned Phlego only as a limestone replacement to reduce clinker-related emissions and make more efficient use of raw materials. Now, she and Hay are also exploring its potential as an affordable, abundant alternative to today’s constrained SCM supply. Phlego is engineered to perform reliably in both applications, without requiring plants to overhaul their manufacturing processes.  

“In hard-to-abate sectors like cement, the fastest path to revolutionary impact comes from compatibility rather than radical change,” Vanorio says. “A drop-in solution dramatically reduces deployment risk.”

Vanorio is also an associate professor, by courtesy, of civil and environmental engineering and a senior fellow at the Precourt Institute for Energy. Hay is affiliated with the Department of Earth and Planetary Sciences, where Liang is a postdoctoral scholar.

Other Accelerator project team members include Alberto Salleo, the Hong Seh and Vivian W. M. Lim Professor in the School of Engineering and a professor of photon science, and Matteo Cargnello, an associate professor of chemical engineering and, by courtesy, of materials science and engineering. Salleo and Cargnello are both senior fellows at the Precourt Institute for Energy.

Precourt’s Strategic Energy Alliance funded Vanorio’s research on Phlego prototypes. Stanford University does not endorse any non-Stanford entities, programs, products, or services listed in the article.