Using Coal Ash and Carbon Dioxide to Make Cement

A New Technology Aims to Shrink One of Construction’s Biggest Carbon Footprints

Research engineer Casey Jones inspects a drying belt at Alithic's demonstration plant in Madison, Wisconsin, which combines carbon dioxide from the atmosphere with ash and other industrial wastes to make a low-cost, carbon-negative building material.  Chris Hubbuch/Wisconsin Energy Institute

A University of Wisconsin–Madison spinoff is advancing a technology that turns two major industrial pollutants—carbon dioxide and coal ash—into a building material that can replace a key component of conventional cement and cut greenhouse-gas emissions associated with concrete production.

Alithic, founded in 2023 by UW–Madison engineers, uses a chemical process that pulls CO₂ directly from the air and reacts it with industrial waste like coal ash to produce supplementary cementitious material (SCM). The resulting mineral product acts as a binding agent in concrete, offering strength comparable to, or in some cases exceeding, traditional Portland cement while sequestering carbon rather than releasing it.

Concrete is central to global infrastructure but is also a major climate challenge. Ordinary Portland cement is responsible for roughly 7%–8% of global CO₂ emissions due to the high-heat calcination of limestone and fossil fuel use in clinker production. In contrast, Alithic’s process operates at ambient temperatures in a modified capture unit, binding carbon into solid mineral form with modest energy requirements.

Handling Two Waste Streams at Once

At a demonstration plant in Madison, the five-person Alithic team is refining the process by running ambient air over a sodium hydroxide solution that absorbs CO₂. That carbonated solution is then mixed with coal ash or other industrial wastes, where the CO₂ mineralizes with silicates and calcium to form SCM. A belt filter dries the product while recycling the alkaline solution for reuse.

Coal ash—a by-product of coal-fired power plants—poses environmental risks in landfills and containment ponds, including groundwater contamination. By upcycling this material into construction inputs, Alithic’s approach addresses two waste streams at once.

Prof. Rob Anex explains the process for creating a useful cement ingredient from two separate waste streams. Chris Hubbuch/Wisconsin Energy Institute

Unlike most direct-air-capture technologies, which require significant energy, the Alithic method is comparatively efficient, according to cofounder and engineering professor Rob Anex. The company has moved from laboratory proof-of-concept to an operational demonstration plant and is now fundraising to build a ton-scale pilot facility at the National Carbon Capture Center in Wilsonville, Alabama.

Alithic’s product has attracted attention in the cleantech community: The company was named to Cleantech Group’s list of 50 early-stage innovators working on breakthrough sustainability technologies and was a finalist in the CEMEX Ventures green construction startup competition.

While the company initially pursued carbon removal as part of its business model—including signing a contract to remove 285 tons of CO₂ for corporate buyers—it has shifted focus toward commercial SCM sales. As Anex notes, customers are primarily motivated by performance and cost rather than climate benefits, although the embedded carbon capture is a valuable differentiator.

Alithic’s development comes amid global innovation in low-carbon cement and concrete technologies, including startups using electrochemical processes to avoid CO₂ emissions entirely and industry efforts to reduce clinker and harness industrial by-products.

If scaled successfully, these alternatives could play an essential role in decarbonizing one of the hardest-to-abate sectors and help shift the construction industry toward materials that build infrastructure and combat climate change simultaneously.