Chemical model for cement-based materials: Temperature dependence of thermodynamic functions for nanocrystalline and crystalline C-S-H phases

Journal Article · Tue Jun 15 00:00:00 EDT 2010 · Cement and Concrete Research

DOI:https://doi.org/10.1016/j.cemconres.2009.12.004· OSTI ID:21344766

Blanc, Ph ^[1]; Bourbon, X ^[2]; Lassin, A; Gaucher, E C ^[1]

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1. BRGM, 3 Avenue Claude Guillemin, 45060 Orleans Cedex 2 (France)
2. ANDRA - Scientific Division, 1-7 Rue Jean Monnet, Parc de la Croix Blanche, 92298 Chatenay Malabry Cedex (France)

In the context of waste confinement and, more specifically, waste from the nuclear industry, concrete is used both as a confinement and as a building material. Its exposure to high temperatures makes its geochemical behavior difficult to predict over large periods of time. The present work aims to elucidate the solubility constants, as a function of temperature, for the phases of the system CaO-SiO{sub 2}-H{sub 2}O. For the nanocrystalline phases, the present work investigates the existence of compounds of fixed composition, possibly in a metastable state. The question of whether the nanocrystalline C-S-H phases correspond to a series of phases of discrete composition or a solid solution is discussed and compared to the possible influence of impurities in the solid phases. For the crystalline phases, having established that the currently available values of thermodynamic properties were not consistent, we show that their refinement leads to a better agreement with the literature data. From the refined thermodynamic properties of crystalline C-S-H, a polyhedral decomposition model is developed. It enables to estimate the enthalpy of formation and the heat capacity of nanocrystalline C-S-H phases. Finally, verification shows that such phases remain unstable compared to the crystalline phases, at room or higher temperatures. A comparison, based on reaction enthalpies derived from experimental data indicates that predicted values for nanocrystalline C-S-H are in close agreement with experimental data. By estimating the properties of okenite and truscottite with the model developed in this study, we have been able to complete the CaO-SiO{sub 2}-H{sub 2}O phase diagram with a reasonable agreement with the literature. The case of jaffeite remains open to discussion. Finally, for the hydrate C2SH,alpha, the model predicts a transition with hillebrandite at 159 deg. C, in contradiction with the hypothesis of C2SH,alpha metastability.

• OSTI ID: 21344766
• Journal Information: Cement and Concrete Research, Vol. 40, Issue 6; Other Information: DOI: 10.1016/j.cemconres.2009.12.004; PII: S0008-8846(09)00350-0; Copyright (c) 2009 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; ISSN 0008-8846
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CALCIUM OXIDES
CALCIUM SILICATES
CEMENTS
CONCRETES
CONFINEMENT
CRYSTALS
FORMATION HEAT
HYDRATES
METASTABLE STATES
NANOSTRUCTURES
NUCLEAR INDUSTRY
PHASE DIAGRAMS
RADIOACTIVE WASTES
SILICON OXIDES
SOLID SOLUTIONS
SPECIFIC HEAT
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE 0400-1000 K
WATER
ALKALINE EARTH METAL COMPOUNDS
BUILDING MATERIALS
CALCIUM COMPOUNDS
CHALCOGENIDES
DIAGRAMS
DISPERSIONS
ENERGY LEVELS
ENTHALPY
EXCITED STATES
HOMOGENEOUS MIXTURES
HYDROGEN COMPOUNDS
INDUSTRY
INFORMATION
MATERIALS
MIXTURES
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
RADIOACTIVE MATERIALS
REACTION HEAT
SILICATES
SILICON COMPOUNDS
SOLUTIONS
TEMPERATURE RANGE
THERMODYNAMIC PROPERTIES
WASTES