NICOM 4: 4th International Symposium on Nanotechnology in Construction Elastic and Viscoelastic Properties of Calcium Silicate Hydrate Z.C. Grasley 1 , C.A. Jones 2 , X. Li 1 , E.J. Garboczi 3 , and J.W. Bullard 3 1 Zachry Department of Civil Engineering, Texas A&M University, College Station, TX USA zgrasley@civil.tamu.edu, lxd19881102@gmail.com 2 Sandia National Laboratories, Albuquerque, NM USA cajone@sandia.gov 3 Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, MD USA edward.garboczi@nist.gov, jeffrey.bullard@nist.gov ABSTRACT In order to effectively predict the mechanical properties of concrete and other cementitious materials, it is useful to understand the properties and deformation mechanisms on the nano- metric length scale. Through a combined analytical, experimental, and numerical approach, insight has been gained into the nanoscale mechanical properties of calcium silicate hydrate. Using an atomic force microscope, elastic and viscoelastic properties of calcium silicate hy- drate were measured. In addition, a novel computational model was developed to predict the evolution of apparent viscoelastic properties of hydrating cement paste. The results of the experiments and modeling suggest that inherent viscoelastic deformation of calcium silicate hydrate is not necessarily the sole (or primary) source of viscoelastic deformation of cementi- tious materials. Time-dependent dissolution of load bearing phases is suggested as an addi- tional, significant mechanism for the apparent viscoelasticity of cementitious materials. Keywords: C-S-H; Viscoelastic; Computational; FEM 1. Introduction In general, researchers have traditionally attributed the viscoelastic behavior of concrete to the inherent viscoelastic behavior of the calcium silicate hydrate (C-S-H) phase [1]. This un- derstanding of concrete viscoelasticity has led to the development of constitutive models for concrete viscoelastic behavior such as the solidification theory [2, 3]. Other mechanisms for the time-dependent deformation of cementitious materials have been proposed, however, in- cluding poromechanical effects and dissolution of load bearing phases [4, 5]. Several papers have documented the existence of poromechanical contributions to time-dependent defor- mation of saturated cementitious materials (see e.g. [6-9]), and Grasley and Leung [10, 11] have optimized the poromechanical viscoelastic effects in cementitious materials to enhance mechanical damping properties of concrete under oscillatory loading. However, it is known that the poromechanical components to viscoelastic deformation of cementitious materials are only substantial when the material is fully saturated. Conversely, the dissolution of load bearing phases has not been systematically investigated as a mechanism for viscoelastic de- formation of cementitious materials. The objective of the research reported herein is to evaluate the contribution of inherent C-S-H viscoelastic deformation and load bearing phase dissolution on the overall viscoelastic behav- ior of cementitious materials. Experimental measurements of the creep of C-S-H were per- formed along with computational modeling that evaluated the influence of the dissolution of load bearing phases.