Phytoliths are hydrated silica bodies that are included in plant tissues. Along with another bioliths and volcanic ashes, phytoliths are the main low-density mineral fraction in soils of the Pampa region. The aim of this work was to determine the impact of low-density minerals in the silt fraction on physical properties related with structural stability and porosity. Mixtures with different low-density minerals and clay content were constructed to determine their tensile strength and swelling – shrinkage capacity. The general trend of tensile strength curves showed that the highest the water content, the lowest the tensile strength. This variable showed significant differences at all water contents but at higher water potential. Mixtures with low percentage of light silt fraction showed the highest tensile strength. Near saturation mixtures didn’t show a well defined crash point. Overall, tensile strength was higher with high clay content, low water content and without low-density minerals. Shrinkage curves were obtained for the same mixtures used for tensile strength tests varying the low-density minerals content. In this case, two types of clay were used: illite and swelling clay. Mixtures with illite behave very rigid. Low-density minerals level didn’t modify the matrix volumetric behaviour. The swelling clay curves showed a normal shrinkage behaviour and a higher slope than the illite curves. Thus, clay type appears to be the main factor affecting volume change with water content. For both clay types, mixtures with higher low-density minerals content showed the highest specific volume values. As a conclusion, the surface layer of the Pergamino soil has a high low-density minerals content, which involves negative effects on its tensile strength and therefore on structural stability.

Fil: Cosentino, Diego. Universidad de Buenos Aires. Facultad de Agronomía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Fil: Campos Pecorari, Cecilia. Universidad de Buenos Aires. Facultad de Agronomía; Argentina