Effect of Mellowing and Coal Fly Ash Addition on Behavior of Sulfate-Rich Dispersive Clay after Lime Stabilization

Abstract

Dispersivity and swelling induced by the formation of expansive minerals are deleterious phenomena that can be observed in natural and treated soils. The former is common among sodium-rich soils that are characterized by the deflocculation of the soil’s particles in contact with water. The latter happens due to the growth and hydration of calcium sulfoaluminate minerals as expected in sulfate-rich soils treated with calcium-based stabilizers. The present study assesses the behavior of the Paraguayan sulfate-rich, dispersive as well as expansive, clayey soil after lime stabilization based on an extensive experimental work, which includes unconfined compression, pulse velocity, durability, and free swell tests. This work was designed employing a fractional factorial design in the selection of the experimental runs that enabled statistical evaluation of the influence of the dry unit weight, lime and fly ash content, curing period, mellowing process, and molding moisture content. Results showed that the addition of fly ash, followed by the dry unit weight, were the most influential factors regarding the treated soil’s response in performed tests. In addition, mellowing proved to be essential in reducing the volumetric variation verified in the swelling tests. Also, scanning electron microscopy analysis revealed that ettringite formation was less pronounced when fly ash was added.