Chloride Transport through Cement-Bentonite Barriers

This paper presents experimental results from a number of column tests on cement-bentonite (CB) mixtures permeated with chloride (Cl -). Factors influencing the hydraulic conductivity (k), the hydrodynamic dispersion coefficient (D) and the retardation factor (Rd) are investigated. The significant factors considered are the curing period, seepage velocity (v), reference concentration (CR), and mean particle size (d50). Other factors such as porosity (n) and mix design are also discussed. Results show that a longer curing period lowers all three transport parameters. Furthermore, as the seepage velocity increases, Rd decreases and D increases. The yielding velocity at which mechanical dispersion (Dmd) starts prevailing is observed at about 0.0001 cm/s. Both Rd and D are seen to reduce with increasing CR. Thus, the concept of CR could be used to explain the data scattering in a CB hydrodynamic curve.