Abstract
Water, under conditions of nanoscale confinement, exhibits anomalous dynamics, and enhanced thermal deformations, which may be further enhanced when such water is in contact with hydrophilic surfaces. Such heightened thermal deformations of water could control the volume stability of hydrated materials containing nanoconfined structural water. Understanding and predicting the thermal deformation coefficient (TDC, often referred to as the CTE, coefficient of thermal expansion), which represents volume changes induced in materials under conditions of changing temperature, is of critical importance for hydrated solids including: hydrogels, biological tissues, and calcium silicate hydrates, as changes in their volume can result in stress development, and cracking. By pioneering atomistic simulations, we examine the physical origin of thermal expansion in calcium-silicate-hydrates (C-S-H), the binding agent in concrete that is formed by the reaction of cement with water. We report that the TDC of C-S-H shows a sudden increase when the CaO/SiO2 (molar ratio; abbreviated as Ca/Si) exceeds 1.5. This anomalous behavior arises from a notable increase in the confinement of water contained in the C-S-H’s nanostructure. We identify that confinement is dictated by the topology of the C-S-H’s atomic network. Taken together, the results suggest that thermal deformations of hydrated silicates can be altered by inducing compositional changes, which in turn alter the atomic topology and the resultant volume stability of the solids.
| Original language | English |
|---|---|
| Pages (from-to) | 35621-35627 |
| Number of pages | 7 |
| Journal | ACS Applied Materials and Interfaces |
| Volume | 8 |
| Issue number | 51 |
| DOIs | |
| State | Published - Dec 28 2016 |
Funding
The authors acknowledge financial support for this research provisioned by: Infravation ERA-NET Plus Grant (31109806.0001), the U.S. Department of Transportation via the Federal Highway Administration (DTFH61-13-H-00011), U.S. National Science Foundation (CAREER 1253269 and CMMI 1562066), California Energy Commission (Contract PIR 12-032) and Oak Ridge National Laboratory in the form of Laboratory Directed Research and Development (LDRD) support. The contents of this paper reflect the views and opinions of the authors, who are responsible for the accuracy of the datasets presented herein, and do not reflect the views and/or policies of the funding agencies, nor do the contents constitute a specification, a standard or regulation. This research was conducted in the Laboratory for the Chemistry of Construction Materials (LC2) and the Laboratory for the Physics of Amorphous and Inorganic Solids (PARISlab) at UCLA. As such, the authors gratefully acknowledge the support that has made these laboratories and their operations possible. This manuscript has been coauthored by ORNL, managed by UT-Battelle LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for U.S. Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).
Keywords
- atomistic simulation
- confinement
- silicates
- thermal expansion
- topology