Impact of freeze–thaw cycles on mechanical behaviour of lime stabilized gypseous soils

In seasonally frozen regions, earth structures such as embankments and roads are exposed to periodic freezing–thawing. Most problems with these structures arise from the fact that design approaches are based only on strength without consideration of long-term stability or durability. This study was conducted to investigate the impact of freeze–thaw cycles on the mechanical and mineralogical behaviour of gypseous soils stabilized with lime. The laboratory research associated with this study involved fine-grained soil of different gypsum contents (0, 5, 15 and 25%). The soil samples were stabilized with 3% lime and cured for 28 days at 20 °C. The soil samples were subjected to freeze–thaw cycles following the ASTM procedure. A series of unconfined compression and wave velocity tests were performed. pH, electrical conductivity, water content and volume changes were evaluated. Mercury porosimetry tests and scanning microscopy observations (SEM images) were carried out to determine changes at the microscopic and mineralogical level. Analyses indicated that freeze–thaw cycles reduce the unconfined compressive strength of all the tested samples. Gypseous soil samples lose a substantial amount of their strength after a limited number of freeze–thaw cycles. Moreover, water content during the applied cycles increases and induces significant volume changes with the gypsum content in the soil. The dissolution of gypsum due to water infiltration, crack propagation and ettringite formation was revealed by pH, electrical conductivity and microstructural measurements. These changes in the structure and the mineralogy reduce the durability of gypseous soil samples when subjected to freeze–thaw cycles.