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On the dielectric properties of water confined in cement-like materials

AutorMonasterio, Manuel
DirectorCerveny, Silvina
Palabras clavePortland cement
Water dynamics
Confinement effects
C-S-H gel
Fecha de publicación2015
EditorCSIC-UPV - Centro de Física de Materiales (CFM)
ResumenHydrated cements have pore sizes that range from a few nanometers to microns. The physical and chemical properties of cements (creep, strength, chemical reactivity and shrinkage) are significantly influenced by water molecules in this pore network. Hence, a main task to the cement science is to understand the behavior of water in the pore network to control the physical and chemical properties of cement-based materials. It is known that the structural and physical properties of water near surfaces or confined in small cavities, can be different than those of bulk water. Solid surfaces affect the behavior of water mainly reducing the tetrahedral network of bulk water. However after decades of study, the structure, dynamics and physical properties of this near-surface water remains poorly understood. In this thesis, we focus on the problem of the dynamics of water confined in the nanopores of different sizes of cement-like materials by means of broadband dielectric spectroscopy. This technique has proven to be powerful when studying the reorientation dynamics of polar molecules such as water. In addition, thermal analysis and other spectroscopic techniques have been used to characterize the structure of these materials. This thesis contains four main topics: 1) Dynamics of water in C-S-H gel, the main binding phase of cement materials. From a scientific perspective, the C-S-H gel offers an attractive confinement system where chemical and geometrical effects of the confinement of water can be investigated. In C-S-H gel, the water molecules are trapped mainly in the interlayer space between the highly disordered calcium silicate layers forming the interlayer water. 2) Dynamics of water confined in C-S-H synthesized with the addition of both silica- and amino propyl functionalized nano-particles, before the hydration reaction. 3) Dynamics water confined in tobermorite (natural and synthetic). Structurally Tobermorite is considered an analogue of C-S-H gel. 4) Dynamics of water confined in Portland cements at different water-tocement ratio.
The results of this thesis showed that the nature of water in all these systems split into different relaxations (normally three different dynamics) depending on the different chemical environment and/or physical environment where water molecules are situated. Some relaxations were unequivocally related with water molecules relaxing in small gel pores (< 1 nm) whereas other water molecules were structurally linked to the structure of the different materials analyzed. The main relaxation of water confined in C-S-H, C-S-H with the addition of nanoparticles and tobermorite were faster than the so-called universal beta-relaxation of water. By contrast, water in Portland cement was similar to the universal beta-relaxation of water. The water dynamics in Portland cements showed similar characteristics to that observed in other well-defined confinement systems such as molecular sieves or MCM-41. In this thesis, we will discuss the implications of these observations.
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