Coupling thermodynamics and digital image models to simulate hydration and microstructure development of portland cement pastes

Abstract

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.

Phase Analysis of Portland Cement by Combined Quantitative X-Ray Powder Diffraction and Scanning Electron Microscopy

“…This image file will then be used for the image analysis for determining phase area fraction, phase mass fraction, and phase perimeter http://dx.doi.org/10.6028/jres.121.004 fraction. The resulting image and phase-related data are useful characteristics of the microstructure and for introduction into simulation models like VCCTL [28,29] or THAMES [30]. 8.…”

Microstructural origins of cement paste degradation by external sulfate attack

“…The model used here is an extension of the Thermodynamic Hydration and Microstructure Evolution (THAMES) model recently developed at the National Institute of Standards and Technology (NIST) [39]. THAMES has three main components: (1) a kinetic model of cement clinker phase dissolution, which determines the time dependence of elemental concentrations in the pore solution [41]; (2) thermodynamic speciation calculations to determine the equilibrium composition and abundance of phases other than clinker minerals, including the pore solution [42–44]; and (3) a 3D digital image model for spatially distributing these various phases to represent the microstructure of the binder.…”

“…In this paper, we report a first step in this direction. A thermodynamic-microstructural model of hydration [39] is coupled to a linear thermoelastic finite element model [40] to simulate microstructural evolution by external sulfate attack and to track the microscopic stress field that develops by constrained ettringite growth in the binder porosity. The model is applied here to simulate near-surface sulfate attack of Type I ordinary portland cement binder in a sodium sulfate solution.…”

Rate controls on silicate dissolution in cementitious environments

“…For example, the dissolution behavior of Ca 3 SiO 5 (C 3 S), the primary component in ordinary portland cement (OPC) is well-known to influence aspects ranging from early-age heat release, to microstructure formation and strength development [1][2][3][4][5][6][7][8][9]. On the other hand, due to the significant CO 2 emissions intensity of OPC there is substantial emphasis on replacing OPC by other supplementary cementitious materials (SCMs, e.g., slags, fly ash and calcined clays) in the binder fraction in concrete [10][11][12][13][14][15].…”