Chemical shrinkage of ye'elimite with and without gypsum addition

Mohsen Ben Haha, Frank Bullerjahn, Karen Scrivener
ELSEVIER SCI LTD, 2019
Article

Ye'elimite (Ca4Al6O12SO4 or C(4)A(3)S) is the main hydraulic mineral present in calcium sulphoaluminate cement (CSA). Its reaction is responsible for the (early) hydration and associated cement properties such as the chemical shrinkage. This paper discusses the evolution of chemical shrinkage and related hydration reactions of stoichiometric ye'elimite in the absence and presence of gypsum. The measurements reveal a transitory chemical expansion followed by recovery to the original value for both binders. The shrinkage evolution is linked to the changes within the X-ray amorphous phases formed during hydration. This amorphous component is composed of several metastable hydrates such as aluminium hydroxide gel, which undergo subsequent recrystallization with time. This causes the release of some of the bound water and coincides with the period during which the chemical expansion occurs. (C) 2018 Elsevier Ltd. All rights reserved.

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Mohsen Ben Haha, Frank Bullerjahn, Karen Scrivener
ELSEVIER SCI LTD, 2019
Article

Résumé

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https://infoscience.epfl.ch/record/266445?ln=fr

À propos de ce résultat

Concepts associés (13)

Concepts associés

Chargement

Publications associées (8)

Publications associées

Chargement

Gypse

Le gypse est une espèce minérale composée de sulfate dihydraté de calcium, de formule chimique . Le même mot, gypse, désigne aussi une roche évaporite majeure, constituée principalement du minéral

Hydroxyde d'aluminium

L'hydroxyde d'aluminium, de formule chimique , est la forme la plus stable de l'aluminium dans les conditions normales de température et de pression. L'oxyhydroxyde d'aluminium AlO(OH) et l'alumine

Hydrate

Les hydrates sont des composés formés par l'union d'eau et d'une autre substance, union résultant généralement en un corps neutre, comme certains sels cristallisés. Si l'eau est de l'eau lourde, où l'

Microstructural development of early age hydration shells around cement grains

Emmanuel Gallucci, Prakash Chandra Mathur, Karen Scrivener

An important microstructural aspect of the early hydration of Portland cement (K) is the formation of a shell of hydration products around cement grains. There is, at present, limited information on the mechanism of formation of the shell and of the chemistry of the phases that constitute the shells. Through the use of STEM imaging of early age hydrated cement pastes as early as 2 h, the present work shows that the shells correspond to the first C-S-H type product formed which has a distinct morphology compared to C-S-H formed later when the main reaction occurs (nucleation and growth stage at setting time). The shells form only around the silicate part of the grain and are not empty but filled with a fragile fibrous C-S-H which appears to have a lower (packing) density than the rest of the hydration products. The cement grains underneath the shells are seen to react unevenly and the hydration seems to follow a reaction front, leaving striations up to 1 mu m deep on the grains. Over the long term, the original fragile product seems to densify and gives rise to the usual inner C-S-H. High resolution EDS chemical analysis and mappings were used to get insight into the chemistry associated with the formation of these early age products. The C/S ratio of all C-S-H (inner and outer shell) is the same (within the limits of the analysis accuracy) and evolves insignificantly over the first 24 h of hydration. High concentrations of sulfate are associated with the C-S-H formed during the early development of the microstructure, but these decrease later, the sulfate being mainly incorporated into ettringite. (C) 2009 Elsevier Ltd. All rights reserved.

2010

Chargement

Influence of limestone on the hydration of Portland cements

Emmanuel Gallucci, Barbara Lothenbach, Karen Scrivener

The influence of the presence of limestone on the hydration of Portland cement was investigated. Blending of Portland cement with limestone was found to influence the hydrate assemblage of the hydrated cement. Thermodynamic calculations as well as experimental observations indicated that in the presence of limestone, monocarbonate instead of monosulfate was stable. Thermodynamic modelling showed that the stabilisation of monocarbonate in the presence of limestone indirectly stabilised ettringite leading to a corresponding increase of the total volume of the hydrate phase and a decrease of porosity. The measured difference in porosity between the "limestone-free" cement, which contained less than 0.3% CO2, and a cement containing 4% limestone, however, was much smaller than calculated. Coupling of thermodynamic modelling with a set of kinetic equations which described the dissolution of the clinker, predicted quantitatively the amount of hydrates. The quantities of ettringite, portlandite and amorphous phase as determined by TGA and XRD agreed well with the calculated amounts of these phases after different periods of time. The findings in this paper show that changes in the bulk composition of hydrating cements can be followed by coupled thermodynamic models. Comparison between experimental and modelled data helps to understand in more detail the dominating processes during cement hydration.

2008

Chargement

μic: A new platform for modelling the hydration of cements

Shashank Bishnoi, Karen Scrivener

A new modelling platform, called mu ic has been developed to model the microstructural evolution of hydrating cement paste. The platform uses the vector approach and can be used for modelling particulate reactions including the hydration of many different cementitious systems involving millions of particles. In this paper, the ideas behind the development of mu ic and its main features are presented. The complexity of cement hydration and the gaps in our current understanding of cement played an important role in its design, so the platform has the primary objective of aiding, rather than replacing experiments. The platform is highly customisable as users can define materials, particles and reactions and choose or create external plugins to define models of microstructural development The platform can be used to test the validity of hypotheses by easily formulating them as input and comparing simulations with experimental results. This paper presents the design of mu ic and examples that demonstrate the important features of its performance and design. (C) 2008 Elsevier Ltd. All rights reserved.

2009

Chargement