This experimental study investigates the swelling behaviour of an 80/20 sand/bentonite mixture and the associated fabric evolution under different hydro-chemo-mechanical loadings. Free and confined swelling tests are performed on specimens compacted to different dry densities and wetted with different pore fluids. Controlled suction confined swelling tests are performed to determine the suction-swelling pressure relationship for two different densities. An extensive microstructural characterisation is performed to relate the observed swelling behaviour to the evolution of the different pore networks during wetting. Based on the microstructural analysis, an expression is proposed to determine the relative dry density of the bentonite. This parameter enables comparisons of the data on the swelling of different bentonite-based materials prepared at different mixing ratios. A unique relationship is determined to fit all of the experimental data satisfactorily. The results reveal that the generated swelling pressure depends on the applied matric suction and on the chemical composition of the pore water. At a low dry density, the mixture in contact with aqueous solutions loses most of its swelling capacity. At a higher dry density, the swelling capacity of the mixture is better preserved.