title: Confined Water in Layered Silicates: The Origin of Anomalous Thermal Expansion Behavior in Calcium-Silicate-Hydrates.
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.
authors.affiliation: Laboratory for the Chemistry of Construction Materials (LC2), Department of Civil and Environmental Engineering, University of California , Los Angeles, California 90095, United States.|Laboratory for the Physics of Amorphous and Inorganic Solids (PARISlab), Department of Civil and Environmental Engineering, University of California , Los Angeles, California 90095, United States.
authors.forename: N M Anoop
authors.identifier: http://orcid.org/0000-0003-1500-4947
authors.initials: NM
authors.lastname: Krishnan
authors.affiliation: Laboratory for the Chemistry of Construction Materials (LC2), Department of Civil and Environmental Engineering, University of California , Los Angeles, California 90095, United States.|Laboratory for the Physics of Amorphous and Inorganic Solids (PARISlab), Department of Civil and Environmental Engineering, University of California , Los Angeles, California 90095, United States.
authors.forename: Bu
authors.initials: B
authors.lastname: Wang
authors.affiliation: Laboratory for the Chemistry of Construction Materials (LC2), Department of Civil and Environmental Engineering, University of California , Los Angeles, California 90095, United States.
authors.forename: Gabriel
authors.identifier: http://orcid.org/0000-0002-6125-6726
authors.initials: G
authors.lastname: Falzone
authors.affiliation: Oak Ridge National Laboratory , P.O. Box 2008, Oak Ridge, Tennessee 37831, United States.
authors.forename: Yann
authors.initials: Y
authors.lastname: Le Pape
authors.affiliation: School of Sustainable Engineering and the Built Environment, Arizona State University , Tempe, Arizona 85281, United States.
authors.forename: Narayanan
authors.initials: N
authors.lastname: Neithalath
authors.affiliation: Department of Mechanical and Aerospace Engineering, University of California , Los Angeles, California 90095, United States.
authors.forename: Laurent
authors.initials: L
authors.lastname: Pilon
authors.affiliation: Laboratory for the Physics of Amorphous and Inorganic Solids (PARISlab), Department of Civil and Environmental Engineering, University of California , Los Angeles, California 90095, United States.
authors.forename: Mathieu
authors.initials: M
authors.lastname: Bauchy
authors.affiliation: Laboratory for the Chemistry of Construction Materials (LC2), Department of Civil and Environmental Engineering, University of California , Los Angeles, California 90095, United States.|California Nanosystems Institute (CNSI), University of California , Los Angeles, California 90095, United States.
authors.forename: Gaurav
authors.initials: G
authors.lastname: Sant
keywords: atomistic simulation; confinement; silicates; thermal expansion; topology