On the intrusion of polyethylene glycol during osmotic tests

Abstract

In the laboratory, semi-permeable membranes and polyethylene glycol (PEG) solutions are used for applying suction in soils using the osmotic technique. In this study, the pore structures of cellulose semi-permeable membranes with molecular weight cut-off values of 3500 and 14 000 were examined via an atomic force microscope (AFM). Fourier transform infrared (FTIR) spectroscopy was used to identify any degradation of PEG molecules with elapsed time. Freshly prepared PEG solutions and solutions aged for 15 days were considered for this purpose. Osmotic tests were carried out on initially saturated MX80 bentonite specimens at two suction levels (0·44 and 7·04 MPa). Comparison of the AFM images of the semi-permeable membranes before and after the osmotic tests clearly revealed that the pore size of the semi-permeable membranes increased significantly, particularly at the higher applied suction that enabled passing of PEG molecules into the clay specimens. FTIR spectrums of PEG 20 000 and PEG 6000 did not provide any evidence of degradation of the PEG molecules with elapsed time.