The coupling effects of electric field and clay mineralogy on clay aggregate stability

Abstract

This paper aims to investigate the effect of clay mineralogy on aggregate stability under the consideration of soil particle surface electric field in electrolyte solution. Aggregates of montmorillonite, kaolinite, and their compounds in different mass ratio were used as experimental materials. The degree to which the aggregates broke down under different electrolyte concentrations was evaluated both qualitatively and quantitatively. The aggregate breakdown process was observed with a video microscope. Furthermore, the percentage of particles (micro-aggregates and single particles) in diameter of <10, <5, and <2 μm to the total sample mass were measured based on Stokes equation. Different electrolyte concentrations correspond to different surface potential values around the particle surface. (1) The amount of released small particles for aggregate of clay compounds was several times higher than that for montmorillonite aggregate after breakdown. (2) Under high surface potential conditions, aggregate breakdown in a way of explosion was observed, and the critical surface potential values for the explosion increased with the increase of kaolinite content in aggregates. (3) The content of released particles for clay compound aggregates with high kaolinite content was much higher than that for aggregates with low kaolinite content under high surface potential values. The coupling effects of electric field and clay mineralogy determined the aggregate stability of montmorillonite and clay compounds. This indicated that soil aggregates with relatively high silt content would be less stable than those with relatively high clay content under heavy rainfall; the most erosive soil might not be clay soils, but the silt soils, especially those under sudden storm after long-time drought.