Cement Research Finds Strength in Defects
TUESDAY, JANUARY 24, 2017
Researchers at Rice University are zeroing in on a mineral used by the ancient Romans in cement in order to understand how modern cement can be made stronger and more resistant to cracking.
|
|
| Multiscale Materials Laboratory/Rice University |
|
Tobermorite particles often exhibit what are called screw dislocations, defects in layers at the molecular level. |
Tobermorite is a crystalline mineral that’s analogous to the calcium-silicate-hydrate of cement, and was once used in the concrete made by the Romans. Materials scientist Rouzbeh Shahsavari, at Rice University’s Multiscale Materials Laboratory, recently published new research looking at the atomic structure of tobermorite in hopes of better understanding how it helped to make ancient Roman concrete an “extraordinarily durable, high-performance composite,” as some researchers have called it.
Defects Lead to Strength
Shahsavari’s new work, published in the American Chemical Society journal ACS Applied Materials and Interfaces, describes how tobermorite particles often exhibit what are called screw dislocations, defects in layers at the molecular level.
The defects don’t cause overall weakness in the material, though: In fact, they lead to the mineral’s ultimate strength. Where layers of tobermorite slid past each other, the screw defects would cause them to catch, like teeth. Thus, stress was distributed without the material actually cracking.
“The insight we get from this study is that unlike the common intuition that defects are detrimental for materials, when it comes to complex layered crystalline systems such as tobermorite, this is not the case,” said Shahsavari. “Rather, the defects can lead to dislocation jogs in certain orientations, which acts as a bottleneck for gliding, thus increasing the yield stress and toughness.”
Publication Details
Rice postdoctoral researcher Ning Zhang, who works in Shahsavari’s lab, is lead author of the paper, called “Screw-Dislocation-Induced Strengthening–Toughening Mechanisms in Complex Layered Materials: The Case Study of Tobermorite.” Philippe Carrez, a professor at the Lille University of Science and Technology, Villeneuve d’Ascq, France, is a co-author.
The research was supported by the National Science Foundation.
Tagged categories: Cement; Coating Materials; Colleges and Universities; concrete; Engineers; Research
