A new study published in Nature Communications introduces an exciting material for the construction world: a low-carbon geopolymer composite made with industrial waste. Thanks to advanced 3D printing techniques, this material not only cuts down on waste but also naturally regulates indoor humidity, achieving an impressive moisture buffering value (MBV) of over 14 14 g·m-2·%RH-1.
Study: Low-carbon indoor humidity regulation via 3D-printed superhygroscopic building components. Image Credit: Greerascris/Shutterstock.com
The Problem with Traditional Humidity Control
Controlling indoor humidity is essential for comfortable, healthy living spaces. Typically, buildings rely on energy-hungry systems like dehumidifiers or humidifiers to get the job done. While effective, these systems drive up energy consumption and costs.
An alternative is to use building materials that do the work passively—absorbing excess moisture when the air is humid and releasing it when the air gets dry. This approach can reduce energy loads by up to 30 %. Among these materials, geopolymer composites stand out because they’re not only great at managing humidity but also environmentally friendly.
However, most research into geopolymer materials focuses on their strength and use as an eco-friendly cement alternative. This study flips the focus, looking at how these materials—combined with 3D-printed designs—can create sustainable, high-performance solutions for indoor humidity control.
How the Geopolymer Composite Was Developed
The researchers developed the geopolymer composite by combining potassium silicate solution, metakaolin, and aggregates sourced from marble quarry waste. Binder jet 3D printing technology was used to shape the material into intricate gyroid geometries. These designs were specifically chosen to enhance moisture regulation performance while reducing material usage.
The composite underwent a series of tests to evaluate its properties in detail. Porosity and bulk density measurements assessed the material’s ability to hold moisture through its porous structure. Capillary water absorption and vapor diffusion resistance tests revealed how effectively the composite allowed moisture to move through it. Thermal performance tests, including conductivity and heat capacity assessments, demonstrated how well the material managed temperature fluctuations. Additionally, sorption isotherms quantified the amount of moisture the composite could hold at different humidity levels.
The team used the NORDTEST protocol to measure the material’s moisture buffering value (MBV), comparing the results to conventional materials such as earthen plaster and lime-cement plaster through dynamic hygrothermal simulations. To evaluate real-world performance, they conducted a case study at the Municipal Library of Porto, Portugal. Finally, a life cycle assessment (LCA) was carried out to examine the environmental impact of producing and using the geopolymer composite.
Results and Discussion
The 3D-printed geopolymer composite showed exceptional results, especially in regulating indoor humidity. Thanks to its roughly 30 % open porosity, the material performed far better than traditional building finishes like earthen plaster and lime-cement plaster. To give you an idea, it achieved a moisture buffering value (MBV) of 6.1 g·m-2·%RH-1. By comparison, earthen plaster scored 1.5 g·m-2·%RH-1, while lime-cement plaster managed just 0.36 g·m-2·%RH-1. This means the geopolymer composite can absorb and release much more moisture, making it ideal for passive humidity control.
Its thermal performance was also a standout feature. The composite retained heat better than both earthen and lime-cement plasters, making it a strong choice for moderating indoor temperatures. However, its thermal conductivity was higher than that of some specialized insulating materials, meaning it may not replace them in applications where high insulation is the priority. On top of this, the material absorbed moisture effectively across a wide range of humidity levels, allowing for deeper moisture penetration. This was due to its low resistance to water vapor diffusion, which ensures the material can respond quickly to changes in humidity.
When tested in a real-world setting at the Municipal Library of Porto, Portugal, the results were impressive. When researchers used a 4 cm-thick layer of the geopolymer composite, they found it reduced discomfort hours—periods where indoor conditions are less comfortable—by up to 60 %. It also cut the annual intensity of discomfort by as much as 90 %. These figures highlight how this material can significantly improve indoor air quality and comfort without the need for energy-intensive solutions like dehumidifiers or air conditioning.
From an environmental perspective, the geopolymer composite had a slightly higher global warming potential (GWP) compared to traditional lime-cement and earthen plasters. However, it’s still a much greener option than phenolic-based materials often used in 3D printing. The researchers also pointed out that there’s room to make it even more sustainable. By swapping out some of the activators and precursors in the formula for secondary byproducts, the composite’s carbon footprint could be reduced even further, making it an even better choice for eco-friendly construction.
Conclusion
This study highlights the potential of 3D-printed geopolymer composites as a sustainable building material. By combining industrial waste with advanced manufacturing techniques, researchers created a material that excels in humidity regulation, reduces energy consumption, and improves indoor air quality.
While the composite does have a slightly higher environmental impact than some traditional materials, its advantages in performance and its lower emissions compared to phenolic-based materials make it a valuable innovation for the construction industry. With further refinements to its formula, this composite could play a key role in making construction more sustainable.
Journal Reference
Posani, M. et al. (2025). Low-carbon indoor humidity regulation via 3D-printed superhygroscopic building components. Nature Communications, 16(1). DOI: 10.1038/s41467-024-54944-1, https://www.nature.com/articles/s41467-024-54944-1
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