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A Model of Phase Stability, Microstructure and Properties During Leaching of Portland Cement Binders

Published

Author(s)

Pan Feng, Pan Feng, Jeffrey W. Bullard

Abstract

A new model of 3D cement paste microstructure development is described and used to simulate the influence of leaching on hydrated cement pastes. In contrast to recent leaching models that have used empirical rules for phase dissolution, this model uses continual thermodynamic speciation and phase stability calculations to guide the microstructural changes that happen throughout hydration and subsequent exposure to low-pH solutions. This novel aspect of the model enables it to predict not only the well-known phase instability of calcium hydroxide at the onset of leaching, but also the detailed compositional and volumetric changes of C–S–H gel and other calcium, aluminate, and sulfate phases. Besides tracking the compositional and microstructural changes, we use the evolving microstructure as input to calculate changes in the relative diffusivity and effective Young’s modulus of the binder using established finite difference and finite element models. The results are broadly consistent with previous experimental and modeling investigations of leaching. In particular, the leaching process can be roughly divided into initial, intermediate, and final stages, each of which has distinct degradation characteristics and consequences for mechanical and transport properties. The thermodynamic basis of the model makes it readily extensible to simulate a wide range of cementitious materials and degradation phenomena, so we discuss its potential as a virtual microprobe for use with continuum-scale service life models of concrete elements.
Citation
Cement and Concrete Composites
Volume
49

Keywords

cement, hydration, leaching, computer simulation, elastic properties, transport properties

Citation

Feng, P. , Feng, P. and Bullard, J. (2014), A Model of Phase Stability, Microstructure and Properties During Leaching of Portland Cement Binders, Cement and Concrete Composites, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=914016 (Accessed May 31, 2023)
Created May 15, 2014, Updated February 19, 2017