A breakthrough imaging method is giving scientists a detailed, real-time view into how cement paste absorbs carbon dioxide, tracking moisture, cracking, and chemical reactions as they unfold. This cutting-edge 5D imaging approach could be a game-changer for designing stronger, more sustainable concrete.
Study: Operando 5D Tomography Uncovers Carbonation-Driven Water Transport And Cracking In Hydrated Cement Paste. Image Credit: NP27/Shutterstock.com
In a study recently published in Communications Materials, researchers introduced the first-ever fully simultaneous operando five-dimensional (5D) imaging technique, capturing 3D structure, dual imaging modalities, and time to observe the coupled processes driving carbonation in hydrated cement paste.
This technique offers direct, high-resolution insight into the physical and chemical interactions that determine how effectively concrete captures CO2.
Why Concrete Recycling Matters
As global demand for concrete climbs, so do its environmental costs. Cement production alone accounts for 5–7 % of global CO2 emissions.
The construction sector also generates 4–6 billion tons of construction and demolition waste (CDW) annually, with concrete making up 70–85 % of that total. That translates to roughly 2.8–5.1 billion tonnes of concrete available each year for carbonation-based CO2 capture, making recycled concrete a key player in reducing emissions.
One major strategy is using CDW as an aggregate in new concrete. This promotes a circular material economy and reduces the need for virgin resources.
However, recycled aggregates are more porous and absorbent, which can affect performance. Accelerated carbonation has shown promise in improving these properties by enhancing mechanical stability and sealing pores.
The Challenge of Understanding Carbonation
To optimize carbonation in recycled materials, researchers need to fully understand the thermo-hydro-chemo-mechanical (THCM) processes involved. That includes moisture and gas transport, mechanical damage, and chemical reactions.
Traditional methods like thermogravimetric analysis (TGA), X-ray diffraction (XRD), and pH indicators offer limited spatial resolution.
Raman spectroscopy delivers chemical sensitivity but lacks depth penetration. X-ray CT can map carbonation fronts, but doesn’t capture moisture movement.
Neutron imaging, on the other hand, excels at moisture tracking. Recently, dual-modality systems like NeXT have enabled simultaneous neutron and X-ray tomography, combining these complementary capabilities.
Inside the Study: Simulating Real-World Conditions
The research team used a new operando 5D imaging setup to study carbonation in cement paste under realistic industrial conditions (80?°C and 0 % relative humidity) that mimic accelerated carbonation environments.
They prepared two CEM I 52.5 cement paste specimens with a 0.50 water-to-binder ratio. After 28 days of curing, one sample was exposed to CO2 at high temperature and low humidity for 10 hours, while the second sample underwent similar conditions but in a nitrogen atmosphere for 3 hours (with longer-term behavior estimated via modelling).
Before carbonation, samples were vacuum-saturated and oven-dried to establish reference masses. Controlled drying achieved a 70 % saturation level to facilitate CO2 diffusion. After re-equilibration, neutron and X-ray tomography experiments began two weeks later.
The team designed a custom carbonation chamber capable of maintaining tight control over temperature, humidity, and CO2 concentration during active imaging, enabling high-speed, high-resolution imaging using the NeXT instrument.
This setup captured neutron (21?µm) and X-ray (15?µm) tomographies every 25 minutes, with enhanced signal quality via multiple-angle projection averaging and advanced reconstruction algorithms.
Key Findings: Cracking, Moisture, and Carbon Capture
This method provided unprecedented insight into how water, heat, chemical reactions, and mechanical stress interact during carbonation. Among the key results:
- Coupled moisture and chemical dynamics: Neutron imaging revealed the release of bound water from hydrate decomposition. X-ray imaging captured cracking and its eventual partial self-healing.
- Quantifying carbonation front progression: The process started as diffusion-controlled, then slowed as moisture accumulation and pore clogging by calcium carbonate altered the transport pathways. This led to a bilinear reaction front, showing that purely diffusive models are insufficient for accurate prediction.
- Crack formation tied to moisture dynamics: Cracks appeared after ~200 minutes and were most prominent in low-moisture zones. These were attributed to drying shrinkage rather than direct CO2 effects, highlighting the role of THCM coupling.
- First-ever distinction of bound vs. free water during carbonation: Combining neutron tomography with TGA allowed researchers to separate moisture types in real time, offering deeper insight into reaction kinetics and moisture redistribution.
What This Means for Sustainable Concrete
This study marks a major step toward designing carbon-optimized cement-based materials, particularly in the context of recycled concrete.
By capturing detailed, real-time information on how carbonation progresses and affects structure, the operando 5D imaging method supports more accurate predictive models and smarter carbon capture strategies.
The insights gained here can help engineers and researchers better tailor carbonation conditions to maximize CO2 sequestration and structural durability, contributing to both emissions reduction and resource circularity in the construction industry.
Journal Reference
El Faqir, C., Tengattini, A., Huet, B., Briffaut, M., & Dal Pont, S. (2026). Operando 5D Tomography Uncovers Carbonation-Driven Water Transport And Cracking In Hydrated Cement Paste. Communications Materials. DOI: 10.1038/s43246-025-01060-2, https://www.nature.com/articles/s43246-025-01060-2
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