Nanostructure and Irreversible Colloid Behavior

This work was carried out at the University of Granada and published as “Nanostructure and Irreversible Colloidal Behavior of Ca(OH)2: Implications in Cultural Heritage Conservation,” Langmuir, 2005, 21, 10948-10957, by C. Rodriguez-Navarro, E. Ruiz-Agudo, M. Ortega Huertas, and E. Hansen.

It was shown that the irreversible aggregation associated with drying of either slaked lime putty or the industrial process resulting in the formation of dry hydrated lime is detrimental to the colloidal behavior of Ca(OH)2. It strongly affects the rheological properties of hydrated lime putty and the resulting mortar/plaster performance. In particular, it affects the plasticity of lime putties.

It is important to note that the observations on crystal coarsening required characterization of the lime putty both before and after drying, and the hydrated lime before and after constituting a putty by mixing in water. Special sample preparation is required for tests sensitive to drying, including scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen adsorption (by BET method); these methods required freeze-drying as opposed to oven drying if the crystal shape and size of calcium hydroxide in lime putty are to be characterized. In this respect, previous results in the literature that have not used freeze-drying might not provide an accurate representation of the microtexture of portlandite crystals in a wet putty.