Effects of lime and cement treatment on the physicochemical, microstructural and mechanical characteristics of a plastic silt

• A macro–micro investigation depicts the effect of binder addition to a silty soil.
• Binder addition modifies the soil fabric, density and porosity.
• A hydrated gel develops in response to the binder addition.
• This gel forms a continuous network similar to a “honeycomb” type of structure.
• This gel modifies the soil fabric and mechanical strength.

Stabilization using lime and cement is a widespread technique that provides civil engineering applications for soils with poor geotechnical performance. This article describes the effects of a combined lime + cement treatment on both the characteristics and properties of a plastic silt. A multi-scale approach was implemented and the mechanical, microstructural and physicochemical changes were investigated. To carry out these tasks, unconfined compressive strength measurements were conducted. The modifications caused by this treatment on the microstructure could be characterized by means of scanning electron microscope (SEM) observations of the soil composition, through element distribution maps and mercury intrusion porosimetry (MIP) analyses. The physicochemical evolution has been monitored by X-ray diffraction (XRD) analyses. Within the silt, clay particles surround the coarsest particles in order to form millimeter-sized agglomerates, around which binders are deposited. During the curing period, the formation of C-(A)-S-H becomes readily apparent. These phases are detected in the form of a gel that provides continuity throughout the material; as such, the material displays a “honeycomb” type of microstructure. The mechanical properties of the treated soil are indeed affected by this microstructural organization. The post-treatment improvement in mechanical performance therefore proves to be significant.