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Research Papers

Constitutive Stiffness Characteristics of Cement Paste as a Multiphase Composite System—A Molecular Dynamics-Based Model

[+] Author and Article Information
Ingrid M. Padilla Espinosa

Nanoengineering Department,
Joint School of Nanoscience
and Nanoengineering,
North Carolina A&T State University,
2907 E Gate City Boulevard,
Greensboro, NC 27401
e-mail: impadill@aggies.ncat.edu

Wayne Hodo

Engineering Research and Development Center,
3909 Halls Ferry Road,
Vicksburg, MS 39180
e-mail: Wayne.d.hodo@usace.army.mil

John S. Rivas Murillo

Nanoengineering Department,
Joint School of Nanoscience
and Nanoengineering,
North Carolina A&T State University,
2907 E Gate City Boulevard,
Greensboro, NC 27401
e-mail: jrmurill@ncat.edu

A. M. Rajendran

Department of Mechanical Engineering,
University of Mississippi,
Oxford, MS 38677
e-mail: raj@olemiss.edu

Ram V. Mohan

Mem. ASME
Nanoengineering Department,
Joint School of Nanoscience
and Nanoengineering,
North Carolina A&T State University,
2907 E Gate City Boulevard,
Greensboro, NC 27401
e-mail: rvmohan@ncat.edu

1Corresponding author.

Contributed by the Materials Division of ASME for publication in the JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY. Manuscript received October 3, 2016; final manuscript received March 30, 2017; published online May 25, 2017. Assoc. Editor: Hareesh Tippur.

J. Eng. Mater. Technol 139(4), 041007 (May 25, 2017) (7 pages) Paper No: MATS-16-1282; doi: 10.1115/1.4036588 History: Received October 03, 2016; Revised March 30, 2017

Cement paste is a material with heterogeneous composite structure consisting of hydrated and unhydrated phases at all length scales that varies depending upon the degree of hydration. In this paper, a method to model cement paste as a multiphase system at molecular level for predicting constitutive properties and for understanding the constitutive mechanical behavior characteristics using molecular dynamics is presented. The proposed method creates a framework for molecular level models suitable for predicting constitutive properties of heterogeneous cement paste that could provide potential for comparisons with low length scale experimental characterization techniques. The molecular modeling method followed two approaches: one involving admixed molecular phases and the second involving clusters of the individual phases. In particular, in the present study, cement paste is represented as two-phase composite systems consisting of the calcium silicate hydrate (CSH) phase combined with unhydrated phases tricalcium silicate (C3S) or dicalcium silicate (C2S). Predicted elastic stiffness constants based on molecular model representations employed for the two phases showed that, although the individual phases have anisotropic characteristics, the composite system behaves as an isotropic material. The isotropic characteristics seen from two-phase molecular models mimic the isotropic material nature of heterogeneous cement paste at engineering scale. Further, predicted bulk modulus of the composite system based on molecular modeling is found to be high compared to the elastic modulus, which concurs with the high compression strength of cement paste seen at engineering length scales.

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References

Figures

Grahic Jump Location
Fig. 1

Unit cell molecular structure of (a) CSH—jennite, (b) C3S, and (c) C2S

Grahic Jump Location
Fig. 2

Schematic representation of the methods used to create the two-phase cement paste molecular structures used in this study: (a) approach A and (b) approach B

Grahic Jump Location
Fig. 3

Isotropy relations of the stiffness constants for two-phase structures of CSH and C3S: (a) C11 ≈ C22 ≈ C33, (b) C12 ≈ C13 ≈ C23, and (c) C44 ≈ (C11 − C12)/2. The dotted lines show a linear trend of the constants, short dashed correspond to approach A and long dashed correspond to approach B.

Grahic Jump Location
Fig. 4

Isotropy relations of the stiffness constants for two-phase structures of CSH and C2S: (a) C11 ≈ C22 ≈ C33, (b) C12 ≈ C13 ≈ C23, and (c) C44 ≈ (C11 − C12)/2. The dotted lines show a linear trend of the constants, short dashed correspond to approach A and long dashed correspond to approach B.

Grahic Jump Location
Fig. 5

Bulk modulus of two-phase cement paste composite systems: (a) CSH + C3S and (b) CSH + C2S

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