North / South America
Cement Nanotubes may turn into reality
Jun, 18 2012
Researchers at the Donostia International Physics Center (DIPC), Materials Physics Center (CSIC-UPV/EHU), Tecnalia and University of the Basque Country (UPV/EHU) in Spain, and at the Technische Universität Dresden in Germany have predicted the existence of stable cementitious inorganic nanotubes. Their new approach may help scientists to synthesize nanotubes made of calcium silicate hydrates (C-S-H), proposed as ideal mechanical reinforcements for cement pastes. The work has been recently published in prestigious Advanced Materials journal (DOI: 10.1002/adma.201103704).
When researchers think of nanoreinforcements, carbon nanotubes come as first option. The problem with carbon nanotubes is that they are water insoluble. In order to make them compatible with water chemistry, they must be functionalized in advance. As a consequence, the researcher at Materials Physics Center (CFM) and DIPC, Andrés Ayuela, says "we thought of directly focusing on inorganic nanotubes, in general, and on cementitious nanotubes, in particular, because they have a chemistry that is fully compatible with the aqueous solutions of cements".
Dr. Ayuela explains that "previous experiments on nanotube reinforcements of cements have not fully addressed inorganic nanotubes, which is actually one of our ideas for future development of the field. We are indeed interested in doping cement pastes with cementitious inorganic nanotubes in order to improve their mechanical properties".
By mimicking the layered microstructure of cement, Manzano and co-workers have “roll up” these layers into nanotubular structures. They have modelled cementitious nanotubes with layered structures of portlandite precipitates within the calcium silicate hydrate gel. They have predicted that nanotubes made of portlandite, which contain calcium, are stable and very promising candidates to be synthesised and used as reinforcement nano-fibres in cements.
The team of researchers show that portlandite nanotubes support strain energies similar to those for already synthesized carbon and other inorganic nanotubes. In addition, it is proved that these cementitious nanotubes have good elastic properties, with spring constants three times larger than the values of cement gel under compression. Regarding the tensile strength, portlandite nanotubes can support a stress an order of magnitude larger than the stress supported by ordinary steel fibres. The simulations strongly suggest that reinforcement at the nanoscale by cementitious nanotubes could even prevent from shrinkage to cement pastes.
Being able to calculate the stability of cementitious nanotubes is very important, as a previous step to their synthesis. The authors in their work show the stability and outstanding mechanical properties of these cementitious inorganic nanotubes. Next, they would like to describe the survival of these inorganic nonotubes in different water solutions, where myriad of reactions take place to form the cement paste. These results are expected to help to actually fabricate these nanotubes for doping cement pastes with improved properties.
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