Concrete — the hard, durable masonry that surrounds us everywhere in the form of roads, bridges, dams, and buildings — has a carbon problem. Thanks to a key ingredient, cement, concrete production accounts for roughly eight percent of worldwide CO2 emissions.
Researchers at Sandia hope to trim down the negative climate impact by helping develop several low-carbon cement technologies. A joint project with researchers at Oregon State University, two Indian universities — Indian Institute of Science and Indian Institute of Technology Roorkee — as well as several industrial partners has been funded by Accelerating CO2 Capture, Utilization and Storage Technologies, also known as ACT4. ACT4 is an international initiative supported by funding agencies from sixteen different countries, regions, and provinces.
“Having the opportunity to collaborate internationally is really exciting,” said geochemistry materials scientist Jessica Rimsza. “It feels like we’re pulling together with other people all over the world to tackle an important global challenge.”
Low-carbon and carbon-capturing materials
This three-year project will investigate different pathways to reduce the carbon emissions of cement-based construction. Producing cement releases carbon both from burning fossil fuels to generate heat and as a byproduct of the chemical process used to create cement clinker.
The team’s first path is to develop new low-carbon additives for building materials. One possibility involves mixing the powdered cement with biochar, a plant-based form of charcoal that sequesters carbon.
“We’re looking at biochar that could decrease the amount of cement used, but also produce the same strength and durability as regular cement or concrete,” Rimsza said. “That would help us quite a bit in terms of the carbon footprint.”
Rimsza, an expert in oxide-based materials like glass, ceramics, and cement will work with the team to understand how these additive components change cement’s structure and properties. Having international partners is especially important, she said, because the additive compositions will vary based on the source. “Cement is very local; whatever you build is really dictated by what’s nearby.”
Currently considered a carbon source, building materials could instead act as a carbon sink using the team’s second approach. The team is developing a carbon curing process that exposes precast structures to a high-concentration carbon dioxide environment. As the material cures, it absorbs and sequesters some of the carbon dioxide.
“That changes the minerals formed so you can actually get a higher strength and less permeable material,” Rimsza added. “It’s also a way to use the carbon dioxide collected from other steps in the production process; we’re talking about full carbon capture.”
Applying 3D printing to construction
The last avenue being explored by the team involves changes not to the building materials themselves, but the way they are used in construction.
“Typical concrete or cement-based construction produces a lot of waste,” she said.
According to the Environmental Protection Agency (EPA), construction and demolition-related waste was double the amount of municipal waste generated in 2018, with concrete accounting for more than 65 percent of the wasted material. Using 3D printing technologies, the team can produce only the materials necessary for a specific structure, instead of also creating wasted material seen in current production processes. These technologies also allow for the design of more complex internal geometries that require even less material.
“Instead of using rebar as the structural reinforcement,” Rimsza explained, “you could potentially use 3D printing to create honeycomb-type structures that are self-supported.”
A global problem
The U.S. portion of the project is being funded through the Department of Energy’s Fossil Energy and Carbon Management office. DOE’s Industrial Decarbonization Roadmap identifies cement manufacturing as a critical sector for innovation for the U.S. to meet its goal of net-zero greenhouse gas emissions by 2050.
This project also builds on Sandia’s strategic efforts to advance climate security by advancing the state of the art in industrial decarbonization and carbon capture, utilization, and storage. Historical expertise in the integrity of holes drilled to access resources, mineralization, and subsurface carbon dioxide storage developed for other Sandia missions is now being applied to this challenge.
“We’re leveraging our geoscience and geochemistry-based knowledge here,” Rimsza said. “Surface and carbonation reactions, strengthening, mineralogy, characterization — all those capabilities apply here.”
For Rimsza, this project is especially important because it allows Sandia to get in on the ground floor of addressing cement decarbonization. “There’s a lot of people trying a lot of different ways to tackle this problem because it’s a big one.”
Featured image: 3D floral printing of earth-based cement (Image courtesy of IISc.)