Ingrid Padilla Espinosa – Seminar/PhD Preliminary Defense – Monday, December 11, 2017 at 10:00 A.M.

JSNN – Ingrid Padilla Espinosa – Ph.D. Preliminary Defense/Monday Seminar

Candidate: Ingrid Padilla Espinosa

Advisor and Committee Chair: Ram V. Mohan, Ph.D.

Department: Nanoengineering

Time: 10:00 A.M. – 12:00 P.M.

Location: JSNN 209 Open Room

2907 E. Gate City Blvd., Greensboro, NC 27401

Title: “Mechanical Behavior of Cement Paste at Nanoscale – Reactive Molecular Dynamics Modeling and Experimental Corroborations.”

Abstract:

Cement paste is a hierarchical, multi-scale material where molecular level features at nanoscale from hydration of cement clinkers and evolving microstructures play a key role on its engineering scale characteristics. Material chemistry features in cement paste influence their mechanical behavior; by controlling chemical reactions to result in modified material chemistry molecular structures of cement paste can effectively lead to evolving modified morphologies at microstructure scale level influencing their engineering scale properties. Present research focuses on the development of a method to model cement paste and analyze the mechanical behavior at nanoscale as a composite of hydrated and unhydrated phases, using reactive molecular dynamics. The main purpose of these models is to reveal the molecular interactions of cement paste phases and their effect on localized mechanical performance.

Hydrated product from pure tricalcium-silicate, the main component in cement clinker, will be used as a simplified material and two experimental methods (x-ray diffraction and scanning electron microscopy) will be used to identify, quantify, and map the crystalline and amorphous phases of formed hydrated cement paste constituents. The data obtained from the experimental methods will be used to construct models at molecular level of two and three phases of cement paste. The molecular interactions will be defined by a ReaxFF, a reactive energy field, and the dynamics of the systems, the associated predictive mechanical properties, and the response to different loading conditions will be studied. Finally, experimental characterization based on nanoindentation will be used to calculate the elastic modulus and hardness of individual phases of products of tri-calcium silicate hydration, and compare these calculations to the properties calculated by present molecular dynamics modeling. Preliminary studies of the characterization of hydrated product from tri-calcium silicate show the viability of using the experimental techniques (XRD, SEM, and nanoindentation) and the modeling method investigated for this material system. Modeling methods and processes investigated in the present work are also effective and extendable to other hierarchical material systems with appropriate material chemistry configurations and energy definitions.