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Molecular cement moisture visualization



concrete

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The concrete world that surrounds us is shaped and resistant to chemical reactions that begin when ordinary Portland cement is mixed with water. Now, MIT scientists have demonstrated how to observe these reactions under real-world conditions. A breakthrough that may help researchers find ways to make concrete more sustainable.

This study is “The Lumière brothers̵

7; moment for concrete science,” said co-author Franz-Josef Ulm, professor of civil and environmental engineering. and faculty director of the MIT Concrete Sustainability Hub, said two brothers who were leading the way in the era of cinematic forecasting. It’s like a cinema in Technicolor compared to the black and white photographs of previous research.

Cement in concrete accounts for about 8 percent of the world’s total carbon dioxide emissions. This is comparable to the greenhouse gas emissions produced by most countries. with a better understanding of cement chemistry Scientists can “Change production or change the mix so that concrete has less impact on emissions. or add a mixture that has the ability to actively absorb carbon dioxide,” said Admir Masic, associate professor of civil and Environmental Engineering.

Technology of the future, such as 3D printing of concrete may benefit from this study’s new imaging technique. It shows how the cement hydrates and hardens, said Hyun-Chad Loh, a Masic Lab graduate student who works as a materials scientist with Black Buffalo 3D Corporation. Loh is the author. The first of the studies published in ACS’s LangmoorCollaborated with Ulm, Masic and postdoc Hee-Jeong Rachel Kim.

cement from scratch

Loh and colleagues used a technique called Raman microspectroscopy. to see the specific and dynamic chemical reactions that occur when water and cement are mixed. Raman spectroscopy creates images by projecting high-intensity laser light onto the material. and measure the intensity and wavelength of light when scattered by the molecules that make up the material.

Different molecules and molecular bonds have scattered “fingerprints”. Therefore, the technique can be used to create chemical images of molecular structures and dynamic chemical reactions within materials. Raman spectroscopy is often used to characterize biological and archaeological materials, as Masic studies pearls and other biological materials. and earlier ancient Roman concrete.

Using Raman Microspectroscopy Scientists at MIT observed a sample of ordinary Portland cement placed underwater without interrupting or stopping the hydration process, mimicking the real conditions of concrete use. in general One of the hydration products is called portlandite. Starting from a disorganized phase Absorbed throughout the material Then crystallized, the research team concluded.

Molecular cement moisture visualization

Raman imaging techniques with high time and spatial resolution open up to answer millennial questions about cement chemistry. This high resolution Raman image shows the moisture content of alite (white) that produces CSH (blue) and portlandite (red). Other components are belite (green) and calcite (yellow). Credit: Franz. -Josef Ulm, Admir Masic, Hyun-Chae Chad Loh, et al.

Previously, “scientists were able to study cement hydration only with its average mass properties or with snapshots over time,” Loh said, “but this allowed us to observe all the changes. almost continuously and improve the resolution of our images in space and time.”

For example, calcium-silicate-hydrate, or CSH, is the main ingredient in the cement that holds concrete together. “But it’s very difficult to detect due to its amorphous nature,” Loh explains. “Seeing the structure, distribution and development during the curing process is remarkable.”

build better

Ulm said the work will guide researchers as they experiment with new additives and other methods to reduce concrete’s greenhouse gas emissions: “Instead of Now we can rationalize with this new method whether the reaction happens or does not happen. and chemical interference”

The team will use Raman spectroscopy as they spend the summer testing how well different cement materials are able to trap carbon dioxide, Masic said. But now we have the opportunity to trace CO in cement materials that help us understand where the carbon dioxide goes, what phase it takes, and how it changes so that concrete can be used as a carbon sink.”

Imaging is also important for Loh’s work with concrete 3D printing, which depends on the extrusion of concrete layers in a precise and coordinated measurement process. during which the liquid solution becomes solid concrete.

“Knowing when concrete will emerge is the most important question anyone is trying to understand” in the industry, he says. “We do a lot of trial and error to optimize the design. But examining basic chemistry in space and time is crucial. And this science-based innovation will impact the concrete printing capabilities of the construction industry.”

This work is partially supported by the Kwanjong Education Foundation Scholarship Program.


Tires become graphene that makes concrete stronger.


More information:
Hyun-Chae Loh et al, Biochemical Decomposition Time-Space-Resolved Chemical Deconvolution of the colloidal cement system using Raman Spectroscopy, Langmoor (2021). doi: 10.1021/acs.langmuir.1c00609

Provided by the Massachusetts Institute of Technology.



reference: Molecular cement moisture visualization (2021, June 7) Retrieved June 8, 2021 from https://phys.org/news/2021-06-visualizing-cement-hydration-molecular.html.

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