Microstructure and geotechnical properties of lime-treated expansive clayey soil

The changes in the main geotechnical properties (plasticity, unconfined compressive strength, swelling pressure and permeability) associated with the micro level texture and structure of untreated and lime-treated compacted FoCa clay samples were studied using X-Ray Diffraction, Thermogravimetric Analysis, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) methods. The TEM was found to be a useful tool in the identification of microscopic changes that arise in the lime-treated FoCa clay in comparison to untreated soil. Based on these studies it was identified that the treated FoCa clay has a greater number of packed layers in comparison to untreated or natural FoCa clay. The TEM technique was also useful to observe the appearance of a cementitious phase or pozzolanic phase that is constituted of a hydrate of calcium silicate aluminate (CSAH). SEM results show changes in the morphology of the clay particles and the concentration of calcium is higher on the border of the particles. The focus of this paper is to provide an explanation of improvements of geotechnical properties that arise in the expansive soil behaviour due to the lime-clay reactions, mainly a pozzolanic reaction, using microscopic analysis.

► The association of XRD, TGA, SEM and TEM analysis reveal the mechanisms of the lime-clay reaction.
► Morphological and structural changes were observed with the different stages of the reaction. Geotechnical properties improved with the progression of the reaction and the formation of new hydrate (CSAH).