A swelling pressure cell for X-ray diffraction test

A swelling pressure cell is introduced to measure apparent swelling pressure (ps) and basal spacing of montmorillonite (d001) simultaneously for compacted bentonite during water absorption. Specimens with an initial dry density of up to 1·7 Mg/m3 were prepared with initially oven-dried bentonite powder. Results show that the ps time history curve has four stages: a sharp increase to the peak swelling pressure (pp); a drop to a valley swelling pressure (pv); another increase to the initial swelling pressure for equilibrium (pei); and equilibrium swelling pressure (peq). Meanwhile, d001 changes from 0·98 nm to 1·26 nm, 1·58 nm, 1·90 nm and 4·0 nm gradually during water absorption. Results imply that crystalline swelling of montmorillonite serves an important role for interpretation of ps behaviour of tested specimens. Another testing programme to measure ps compacted bentonite only was conducted using the swelling pressure cell. Results suggest that specimen dry density closely correlates with feature points of ps time history (i.e. pp, pv, pei and peq), which is consistent with results of earlier studies. Importantly, the 2 mm specimen thickness was used, which reduced the test duration to less than 24 h. Evidence from experiments suggests that the swelling pressure cell is a powerful and inexpensive tool for studying the swelling behaviour of compacted bentonite.