Mechanical Behavior of Gypseous Soil Treated with Lime

Gypseous soil is a problematic soil that is very sensitive to moisture variations and loses its strength upon saturation. Lime stabilization is traditionally used to enhance gypseous soils for civil engineering constructions. Studies on gypseous soils stabilized with lime have shown that the effectiveness of the treatment is largely dependent on the lime and gypsum percentages. In this study, an attempt was made to investigate the influence of gypsum and lime percentages on the unconfined compressive strength (UCS) of a fine-grained soil. Mineralogical and microstructural tests were conducted to find the relationship between the mechanical properties and the changes in the microstructures, using X-ray diffraction, scanning electron microscopy and mercury intrusion porosimetry. Different amounts of gypsum (0, 5, 15 and 25% of the dry weight of soil) were added to the soil, which was then treated with three different percentages of lime (3, 5 and 10%). The soil samples were then subjected to curing periods of 2, 7, 28 or 180 days at 20 °C. Results indicated that the influence of gypsum addition on the mechanical properties of soil samples depended not only on the curing period but also on the percentage of lime. The optimum gypsum and lime percent beyond which the improvement in the UCS was reduced was found to be 5%. The micro test results of the treated samples showed the formation of pozzolanic reaction products and ettringite mineral. At first, these new minerals increased the strength of the soil, but with the growth of the ettringite mineral, the strength properties declined. All the evolutions of the mechanical properties were coupled with the results of the micro tests.