Scientists hope to make concrete tougher by studying its defects

"Our study provides the first report on how to leverage seemingly weak attributes -- the defects -- in cement and turn them to highly desired properties, high strength and toughness," said researcher Rouzbeh Shahsavari.
By Brooks Hays   |   Jan. 3, 2017 at 2:45 PM
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HOUSTON, Jan. 3 (UPI) -- Calcium silicate hydrate, or C-S-H, accounts for the strength of cement and cement-based materials. It is the component of cement paste that holds concrete together.

Researchers have struggled to understand the nanostructure of C-S-H, as it is extremely complex. Luckily, tobermorite serves as a naturally occurring crystalline analog. New analysis of tobermorite microstructures suggests C-S-H turns concrete's defects into its strength.

Tobermorite is a calcium silicate hydrate mineral used in Roman concrete. Tobermorite forms in layers, which fuse together to form conglomerate particles. The fused particles posses screw dislocations, or defects which allow layers to slip or slide in response to stress, but also limit each layer's movement. The layers slip until the jagged defects catch and lock.

Computer models revealed the advantages of tobermorite layers with defects over layers without. The brief slides allow the material to dissipate stress across multiple layers without serious deformation or cracking.

Researchers believe C-S-H works in a similar manner, allowing concrete to adjust to stress over hundreds of years without losing its strength.

"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," Rouzbeh Shahsavari, a materials scientist at Rice University, said in a news release. "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."

Shahsavari and his colleagues shared their tobermorite investigation in the journal Applied Materials and Interfaces.

"These latter properties are key to design concrete materials, which are concurrently strong and tough, two engineering features that are highly desired in several applications," Shahsavari added. "Our study provides the first report on how to leverage seemingly weak attributes -- the defects -- in cement and turn them to highly desired properties, high strength and toughness."

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