Stabilizing expansive clay using nano-silica and recycled brick under sulfate exposure

Abstract

Expansive clay soils present significant durability challenges when exposed to sulfate-rich environments due to volumetric instability and mineralogical transformations. Conventional stabilizers such as cement and lime often experience long-term degradation under sulfate attack, primarily through ettringite and thaumasite formation. This systematic review evaluates recent experimental investigations (2022-2025) focusing on the durability performance of expansive clays stabilized using nano-silica (NS) and recycled brick powder (RBP), with particular emphasis on hybrid systems. A structured screening methodology yielded 37 eligible peer-reviewed studies. The review synthesizes mechanical indicators including unconfined compressive strength (UCS), swelling reduction and residual strength under sulfate exposure, alongside microstructural evidence from SEM and XRD analyses. Findings indicate that hybrid NS-RBP systems refine pore structure, promote low Ca/Si ratio C-S-H formation, and significantly reduce sulfate ion diffusion. Compared to cement only system, hybrid binders demonstrate superior strength retention (typically 78-92% under high sulfate concentrations) and enhanced durability stability. Sustainability considerations further support hybrid stabilization due to reduced embodied carbon relative to conventional cement treatment. Despite promising laboratory results, long-term field validation remains limited. The study concludes that Ns-RBP hybrid stabilization represents a technically viable and environmentally responsible solution for sulfate-prone expansive soils.