Effects of aggregate size on the compressibility and air permeability of lime-treated fine-grained soil

The aggregate size of soils is an essential parameter in lime treatment: the thermo-hydro-mechanical behaviour of lime-treated soils can be greatly affected by the aggregate size of soils before treatment. In particular, the compression behaviour and the pore-size distributions of treated soils are expected to be different with different aggregate sizes, leading to different compressibility and permeability of soils. This study aims to investigate the aggregate size effects on the compressibility and air permeability of a lime-treated soil by performing air permeability measurements in oedometer compression tests on a silt with two different maximum aggregate sizes (D_max = 5 and 0.4 mm) and treated with 2% quicklime. The tests were performed on both untreated and treated samples at various curing times (t = 7, 28, 60 and 90 days). Results showed that lime treatment significantly improves the compression behaviour of soil due to both the flocculation process and the pozzolanic reaction. The treated samples prepared with smaller aggregates have higher oedometer modulus, suggesting a better lime distribution and the production of more cementitious compounds. Air permeability of soil is strongly related to the aggregate size: the soil with smaller aggregates can have a value of one order of magnitude lower than that with larger aggregates. Further examination showed that in the case of smaller aggregates, the morphology of macro-pores and the efficiency of air flow are more sensitive to lime treatment.