Coupling thermodynamics and digital image models to simulate hydration and microstructure development of portland cement
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Barbara Lothenbach Laboratory for Concrete and Construction Chemistry, Empa, CH-8600 Dübendorf, Switzerland
Paul E. Stutzman and Kenneth A. Snyder Materials and Construction Research Division, National Institute of Standards and Technology, Gaithersburg, Maryland (Received 26 January 2010; accepted 18 March 2010)
Equilibrium thermodynamic calculations, coupled to a kinetic model for the dissolution rates of clinker phases, have been used in recent years to predict time-dependent phase assemblages in hydrating cement pastes. We couple this approach to a 3D microstructure model to simulate microstructure development during the hydration of ordinary portland cement pastes. The combined simulation tool uses a collection of growth/dissolution rules to approximate a range of growth modes at material interfaces, including growth by weighted mean curvature and growth by random aggregation. The growth rules are formulated for each type of material interface to capture the kinds of cement paste microstructure changes that are typically observed. We make quantitative comparisons between simulated and observed microstructures for two ordinary portland cements, including bulk phase analyses and two-point correlation functions for various phases. The method is also shown to provide accurate predictions of the heats of hydration and 28 day mortar cube compressive strengths. The method is an attractive alternative to the cement hydration and microstructure model CEMHYD3D because it has a better thermodynamic and kinetic basis and because it is transferable to other cementitious material systems. I. INTRODUCTION 1,2
The cement hydration model CEMHYD3D, developed at the National Institute of Standards and Technology (NIST), was the first 3D microstructure model of its kind for simulating cement paste hydration. For more than 10 y it has remained as one of the leading simulation tools for predicting cement paste hydration and property development. Using a digital image model of 3D microstructure, it enables calculation of a wide range of other cement paste properties such as elastic moduli,3 effective DC conductivity,4 and AC impedance response.5 In spite of these successes, the empirical rules lying at the heart of CEMHYD3D cause a number of inherent limitations. First, little information about the kinetics of microstructural change can be determined from the model because the rules by which it changes the microstructure have no intrinsic time scale. In fact, the only way to attach a time scale to the microstructural changes is by calibrating to experimental measurements of the time dependence of the nonevaporable water, chemical shrinka)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2010.41 J. Mater. Res., Vol. 26, No. 4, Feb 28, 2011
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age, or heat release. Second, there is little thermodynamic information in CEMHYD3D that can be used to predict the stable hydration products or how the stability is affected by the temperature or compos
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