In the paper, a multi-scale experimental investigation on the occurrence of carbonation and its effect on chemo-mechanical behaviour of lime-treated soil has been presented. Carbonation affects chemo-mineralogical evolution of lime-treated soils depending on the time scale at which reaction mechanism takes place. In the short term, a progressive carbonation of portlandite is responsible for the formation of calcium carbonate with consumption of available lime for pozzolanic reactions (lime carbonation). In the long term, carbonation of the secondary phases resulting from pozzolanic reactions weakens the bonding effects induced by hydrated compounds (carbonation of secondary reaction products). Mineralogical and microstructural features of lime-treated and carbonated samples have been monitored at increasing curing times by means of microstructural analyses. Triaxial drained compression tests have been performed on treated samples cured in different conditions for short and long term. Mineralogical investigations showed precipitation of calcium carbonate for lime-treated samples exposed to atmospheric CO2 since the very short term. Exposure of lime-treated sample to CO2 after precipitation of hydrated phases favoured decalcification of cementitious compounds and formation of calcium carbonate. In both cases, precipitation of calcite relevantly affects the mechanical behaviour of lime-treated samples. From the observed behaviours, it will be possible to take into account relevant factors for performing the best practice finalized to efficient and durable soil treatment.