MIT researchers have developed a Raman microspectroscopy method for observing the chemistry of cement mixing with water in real-world conditions and in real-time. The breakthrough paves the way for improving the environmental impact of concrete, which leads to 8% of total anthropogenic CO2 emissions.
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New Opportunities in Cement
The new technique will provide opportunities for optimizing cement production, methods and ingredients to make concrete as sustainable as possible. It may also drive new developments in concrete 3D printing, an emerging industrial technology that is yet to realize its full potential.
Improving cement’s sustainability can have a significant impact on the environment due to concrete’s significant share of the blame for environmental damage. Cement in concrete leads to 8% of CO2 emissions, a greater proportion than some countries. Minimizing its impact could make a sizable contribution to resolving the climate emergency.
As well as leading to altered cement production and different ingredients, a better understanding of the chemistry of cement may enable producers to add ingredients that can absorb CO2.
The real-time microscopic image of cement hydrating, mixing, and drying to harden will also help researchers to advance new concrete 3D-printing technologies. This is because the Raman microspectroscopy technique can provide an understanding of cement chemistry in magnified space and time.
With this perspective on the chemical processes involved with cement, researchers can pinpoint the precise time that concrete will set and harden. This enables concrete extrusion to take place at the optimized time and rate and is a question that most working at the forefront of concrete 3D printing technology are trying to answer.
Raman microspectroscopy enabled researchers to inspect the exact chemical reactions in cement mixing with water dynamically as they progressed through time. The technique is used to identify the molecular makeup of samples and can show chemical reactions taking place between molecules.
It works by shining a high-powered laser beam onto the sample and measuring the unique spectrum caused by Raman scattering. Raman scattering is a quantum phenomenon in which photons’ intensities and wavelengths are differently affected by different molecules they interact with.
This means that different molecules and different molecular bonds each have a unique and identifiable “fingerprint” in the Raman spectrum of scattered light. Recording this spectrum with Raman microspectroscopy can reveal information about the molecular structure of samples as well as chemical reactions taking place.
Using Raman microspectroscopy, the research team analyzed a sample of regular Portland cement submerged in water. To mimic real-world concrete usage, the team did not disturb the sample or artificially interfere with the process of cement hydration.
They observed portlandite, one of the hydration products, beginning the process in a disordered phase before percolating through the rest of the material. Then, it crystallized before their eyes.
Prior to this research, cement hydration had only been studied with average properties, or with snapshots of single points in time during the process. The Raman microspectroscopy technique allowed researchers to observe all the chemical changes in the process continuously, improving the resolution of our image of it in space and time.
One key ingredient in cement that can be better understood with this technique was calcium-silicate-hydrate (C-S-H). The primary binding agent in cement has an amorphous nature, making it hard to find and analyze. Using Raman microspectroscopy, the researchers were able to see its structure, distribution, and development during cement’s curing.
Next Steps: Carbon Capture
The scientists behind this research are currently focused on ways to make concrete into a carbon sink with carbon capture technology. Different cementitious materials could capture CO2, ultimately reversing the environmental impact of concrete. Raman microspectroscopy could enable researchers to find a way to make this possible.
References and Further Reading
Ham, Becky (2021) Visualizing Cement Hydration on a Molecular Level. MIT News. [Online] https://news.mit.edu/2021/cement-hydration-molecular-0607
Loh, Hyun-Chae, Hee-Jeong Kim, Franz-Josef Ulm, and Admir Masic. (2021) Time-Space-Resolved Chemical Deconvolution of Cementitious Colloidal Systems Using Raman Spectroscopy. Langmuir. [Online] https://doi.org/10.1021/acs.langmuir.1c00609