عنوان مقاله [English]
In the current research the effects of random polypropylene fibers and lime addition on swelling behavior and expansive pressures of kaolinite using odometer were investigated. Samples were prepared using optimum moisture contents and maximum dry densities determined by conducting standard Proctor compaction tests. Clay samples were mixed with 0.05, 0.1 and 0.2%
fibers and stabilized with 1, 3 and 5 % lime as dry weight of soil. After preparation and setting up samples in odometer, they were inundated with water or 10000-ppm sodium sulphate solution. Results showed that lime addition reduces maximum dry density and increases optimum moisture content of samples whereas fiber addition does not affect these characteristics significantly. Fiber and particularly lime addition substantially reduced swelling potentials and pressures. Optimum lime and fiber percentages determined in this research were 3 and 0.1%, respectively, and the lime showed a much more effective additive than polypropylene fibers in reducing swelling and the associated pressures. This indicates that chemical compounds formed because of lime _ clay reactions are more effective in reducing swelling potential than the physical interactions between polypropylene fibers and clay particles. Inundation of lime-stabilized kaolinite samples with sodium sulphate solution as compared to those samples saturated with water significantly increased swelling potential and pressure. Calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH) compounds formed as a result of dissolution of $SiO_2$ and $Al_2O_3$ from clay particle structure in the environment with a high pH of 12.3 binds clay particles together, reduces their affinity for water absorption and thus swelling. The presence of sodium sulphate results in the formation of ettringite with a substantial potential for water absorption in lime-stabilized kaolinite samples, thus promoting swelling. Ettringite forms in environments with high pH and active sulphates.