Methods to determine hydration states of minerals and cement hydrates

This paper describes a novel approach to the quantitative investigation of the impact of varying relative humidity (RH) and temperature on the structure and thermodynamic properties of salts and crystalline cement hydrates in different hydration states (i.e. varying molar water contents). The multi-method approach developed here is capable of deriving physico-chemical boundary conditions and the thermodynamic properties of hydrated phases, many of which are currently missing from or insufficiently reported in the literature. As an example the approach was applied to monosulfoaluminate, a phase typically found in hydrated cement pastes. New data on the dehydration and rehydration of monosulfoaluminate are presented. Some of the methods used were validated with the system Na2SO4-H2O and new data related to the absorption of water by anhydrous sodium sulfate are presented. The methodology and data reported here should permit better modeling of the volume stability of cementitious systems exposed to various different climatic conditions. (C) 2014 Elsevier Ltd. All rights reserved.

Impact of water activity on the mineralogy of hydrated cement

Luis Guillermo Baquerizo Ibarra

Cement hydrates and their chemically bound water content are sensitive to changes in relative humidity (RH) and temperature. This may cause specific solid volume changes affecting dimensional properties of hydrated cement paste such as shrinkage, swelling and expansion, and therefore impact the performance and the transport properties of cementitious materials. The present thesis studies the impact of drying conditions on the structure and thermodynamic properties of crystalline cement hydrates in different hydration states (i.e. varying molar water contents). The cement hydrates studied include the most important AFm and AFt phases present in different types of cements. A novel multi method approach, including XRD, TGA, DSC, sorption balance measurements, sorption calorimetry and the hydrate pair ¿ humidity buffer method, was used to derive physico-chemical boundary conditions and the thermodynamic properties of the studied hydrated phases. The stability and hydration states of AFm phases depend on the anion content and the exposure conditions. Some phases such as monosulfoaluminate and hydroxy-AFm are very sensitive to different relative humidities. On the other hand monocarboaluminate and strätlingite present very good volume stability with varying RH. Ettringite shows a strong hysteresis during desorption/adsorption, and the thermodynamic properties associated with its decomposition and reformation were determined. The experimental results were included into a thermodynamic model capable of predicting the response of cementitious systems considering the ¿true¿ crystal water content on the final phase assemblage in two different scenarios: i) during hydration, even at conditions where the amount of water added was insufficient for complete hydration, and ii) during drying and re-wetting processes in already hydrated systems. Our work hence opens the possibility to model the response of various cement materials exposed to different climatic conditions and to engineer cementitious systems with respect to minimizing volume changes in the course of drying, which may positively impact properties like drying shrinkage and total porosity.

EPFL2015

Hydration states of AFm cement phases

Thomas Matschei, Mahsa Saeidpour, Karen Scrivener

The AFm phase, one of the main products formed during the hydration of Portland and calcium aluminate cement based systems, belongs to the layered double hydrate (LDH) family having positively charged layers and water plus charge-balancing anions in the interlayer. It is known that these phases present different hydration states (i.e. varying water content) depending on the relative humidity (RH), temperature and anion type, which might be linked to volume changes (swelling and shrinkage). Unfortunately the stability conditions of these phases are insufficiently reported. This paper presents novel experimental results on the different hydration states of the most important AFm phases: monocarboaluminate, hemicarboaluminate, stratlingite, hydroxy AFm and monosulfoaluminate, and the thermodynamic properties associated with changes in their water content during absorption/desorption. This data opens the possibility to model the response of cementitious systems during drying and wetting and to engineer systems more resistant to harsh external conditions. (C) 2015 Elsevier Ltd. All rights reserved.

Pergamon-Elsevier Science Ltd2015

Complexes luminescents de lanthanides avec des dérivés du cyclène comme briques pour l'ingénierie de sondes analytiques biomédicales

This work deals with the engineering of a new luminescent complex of lanthanide, able to be specifically grafted onto biological materials and to emit a characteristic light useful in quantifying the concentration of the target molecules. We have based our molecular design on TbL1, wich possesses a significant quantum yield in water pointing to an efficient intramolecular energy transfer. We have elaborated the synthesis of a ligand derived from L1 and named L3, by functionalizing one of the chromophoric groups into a moiety able to couple the luminescent sensor to biological materials. The synthesis of the complexes was then realized. The thermodynamic study of the ligands L1 and L3, and their terbium complexes in water was made to establish the distribution diagrams and to compare their behaviour, especially at neutral pH. In addition, EuL1 was also investigated and the complexation constants of TbL1, EuL1 and TbL3 in water showed that these molecules are thermodynamically stable in aqueous media. Characterization of EuL3 in the solid state by high resolution luminescence allowed us to determine the geometry of the coordination sphere of the Eu(III) ion, which possesses a distorded C4 symmetry. The detailed study of the Eu(III) ion transitions evidenced two different sites, possibly arising from an equilibrium induced by the competition between a water molecule and the carboxylate function. This interpretation is in line with the measured lifetimes of the Tb(III) and Eu(III) excited states and the calculation of the hydration number of the complexes in aqueous solution. The determination of the energy of the singlet state and triplet states of the ligand, as well as of the emitting levels of the Ln(III) ions in solution showed that their relative values are favorable for a good intramolecular energy transfer. The quantum yields of TbL3 and EuL3, which amount to 2.6 % and 1.4 %, respectively, are lower than those of the complexes with L1, denoting that the presence of the acid function increases losses in the energy transfer. However, these values remain sizeable enough for potential biomedical applications. The study of the intermolecular energy transfer from EuL1, EuL3 and TbL3 to the acceptor Cy5 has proved promising, and the resulting yields were 90 % for EuL1 and 80 % for the complexes with L3.

EPFL2004

Complexes luminescents de lanthanides avec des dérivés du cyclène comme briques pour l'ingénierie de sondes analytiques biomédicales

EPFL2004

Impact of water activity on the mineralogy of hydrated cement

Luis Guillermo Baquerizo Ibarra

EPFL2015