Clay mineralogy as the master variable in lime stabilisation: From layer structure to neoformed C–(A)–S–H phases

The reaction of a clay with lime is, at root, a mineral transformation: the high-pH pore fluid dissolves the aluminosilicate framework and reprecipitates it as a cementitious assemblage. Lime treatment is among the most widely practised soil-improvement techniques, yet its outcome varies enormously with the clay, and existing reviews organise this knowledge around engineering performance rather than the mineral that reacts. This review takes the clay mineral as the organising axis. Setting aside the operational variables — dosage, curing and compaction — that any treatment must also fix, it argues that the first-order control on reactivity is mineralogical. A clay’s reactivity towards lime is decomposed into two competing roles: a calcium sink set by cation exchange capacity and surface area, and a silicon–aluminium source set by layer structure and dissolution kinetics. Their ratio is proposed as a semi-quantitative, dimensionless mineralogical reactivity index that orders the clay-mineral families and rationalises why low-surface-area kaolinite cements more efficiently per unit lime than high-surface-area smectite. The neoformed assemblage — calcium silicate hydrate, its aluminium-substituted analogue C–A–S–H, and calcium aluminate hydrates and carboaluminates — is a mineral-specific fingerprint whose stoichiometry is inherited from the Si : Al ratio the dissolving clay supplies, drawing cement crystallochemistry into soil stabilisation. Durability is decided at the same mineral scale, through the susceptibility of these neophases to carbonation, leaching and sulfate attack. Compared on this common basis, the major clay-mineral families yield a mineralogy–reactivity–neophase–durability chain that points from empirical practice towards predictive, lower-carbon design.