Correlation between large water content and fractal structure in volcanic soils

Abstract:

Volcanic (allophanic) contain amorphous clays (allophanes), issued from the transformation of volcanic materials. These amorphous clays present completely different structures and physical properties compared to usual clays. Allophanes aggregates have peculiar physical features very close to those of synthetic gels: large pore volume and pore size distribution, a high specific surface area and very large water content. We propose that this large water content can be due to the peculiar structure of the allophane aggregates. Because of a large irreversible shrinkage during drying we use the supercritical drying technique to preserve the porous structure and the solid structure of a set of allophanic soils. We study the fractal structure of the allophane aggregates, at the nano scale and show that the most important part of the water content is due to the fractal structure of the porous allophanic aggregates. From the fractal features we calculate the permeability and diffusivity inside the allophanic aggregates and propose that these physical properties could also explain why these soils are able to trap large C content (C sequestration) and pesticides used in crops production.

Año de publicación:

2008

Keywords:

Fuente:

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