Improving the resilience of earthen heritage to severe rainfall through stabilization with hydrated lime and magnesium oxide

Earthen heritage is highly vulnerable to water-induced deterioration, particularly under increasingly intense rainfall events. This study evaluates the effectiveness of hydrated lime (HL) and magnesium oxide-hydrated lime (MgO-HL) stabilization in improving the hydric durability of adobe prepared from earthen material collected at the Campo del Pozzo archeological site, Nazzano, Italy. Adobe specimens with different stabilizer dosages were evaluated through accelerated rainfall simulation, capillary water absorption, and 72 h immersion tests, while mineralogical and microstructural changes were investigated using X-ray diffraction and FE-SEM-EDS analyses. All stabilized samples revealed enhanced resistance to water-induced degradation compared with untreated material, with the best performance achieved by the 15 wt% HL sample and the hybrid formulation containing 10 wt% MgO + 10 wt% HL. These treatments reduced rainfall erosion, limited capillary water uptake, and preserved sample integrity during immersion. Stabilization promoted the formation of C-S-H, C-A-H, and C-A-S-H phases, while Mg-bearing hydrates promoted pore-filling and interparticle cementation. The improved durability is attributed to reduced clay mineral expandability, precipitation of secondary hydrate phases, and aggregation of clay-sized particles. These results demonstrate that HL and MgO-HL stabilization can provide mineralogically compatible strategies for enhancing the durability and resilience of earthen heritage materials.