ABSTRACT

The phase assemblages that form from the hydration of portland cement over time, or from changes in composition, can be predicted by thermodynamic modelling (Lothenbach 2010), or simply by mass balance calculations with some knowledge of the relative stability of the hydrate phases. Thermodynamic modelling can deal with the complexity of cementitious systems and is well suited to predicting the effect of changes in single or several components at once as, e.g. discussed by Damidot et al. (2011). To successfully apply thermodynamic modelling, some knowledge of geochemistry (e.g. which phases can reasonably precipitate or dissolve under the conditions of equilibrium) as well as practical knowledge of the modelling

CONTENTS

11.1 Introduction 485 11.2 Ternary diagrams in the CaO-Al2O3-(Fe2O3-MgO-)

SiO2-SO3-CO2-H2O system 488 11.3 The CaO-Al2O3-SiO2 and C3A-CaSO4-CaCO3 subternary

phase diagrams 489 11.3.1 The CaO-Al2O3-SiO2 subternary phase diagram 490 11.3.2 The C3A-CaSO4-CaCO3 subternary phase diagram 491

11.4 Examples of the application of the CaO-Al2O3-SiO2 and C3ACaSO4-CaCO3 diagrams used in conjunction 492 11.4.1 Portland-pozzolan-limestone cements 492 11.4.2 Comparison with thermodynamic modelling 494 11.4.3 Thaumasite formation 495 11.4.4 Chloride-containing systems 495

11.5 Further components 496 11.6 Excel files for plotting subternary diagrams of hydrated

portland-pozzolan-limestone cements 498 11.7 Conclusions 500 References 500

software being used is needed. For a general overview of the effect of different chemical compositions, ternary phase diagrams provide an effective means of graphical representation of the thermodynamic predictions. The present chapter gives an introduction to how these ternary diagrams are constructed, illustrates their usefulness in predicting the phase assemblage of hydrated cements and offers access to an interactive excel file for performing this in practice.