Impact of organic matter, iron oxides, alumina, silica and drying on mechanical and water stability of artificial soil aggregates. Assessment of new method to study water stability

- New method is proposed for estimation of water stability of soil aggregates.
- Some species considered as aggregate forming factors decrease water stability.
- Water stability of aggregates depends on their size.
- Drying is a dominant factor increasing stability of aggregates.
- Water and mechanical stability of aggregates are not related to each other.

Formation and stability of natural soil aggregates are affected by dozens of different factors and their individual effects are hardly distinguishable. Therefore to observe more clear mechanisms governing their water and mechanical stability, we studied aggregates artificially formed from silt fraction extracted from a loessial soil with various additions of organic matter, iron oxides, alumina and silica. Nondried aggregates that have been never exposed to air moisture below RH = 40% and 100 °C dried aggregates were used. Water destruction kinetics of the aggregates of various sizes was measured by laser diffraction (small aggregates) and by a newly proposed method based on weighing the aggregates during destruction (large aggregates). Destruction kinetics was described by shrinking sphere model and the reaction constant was used as a measure of aggregate water stability. Mechanical stability of aggregates was expressed as their rupture force during penetration tests. Water and mechanical stabilities were not related to each other. Drying increased both water and mechanical stabilities of the aggregates. Mechanical stability of aggregates and their bulk density decreased in most cases with increasing additive doses suggesting that cementing agents loosen aggregate structure. At that same time this structure was generally more water stable. All additives except aluminum increased water stability of large aggregates whereas small aggregates stability decreased at their low doses suggesting that cementing effects are not the same at various size levels. We believe that in natural soils changes of a single cementing agent would lead to similar effects, however this may not be true due to different interactions between various cementing agents present together.