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 $\left({\mathrm{Cl}}^{-}\right)$ . Factors influencing the hydraulic conductivity $\left(k\right)$ , the hydrodynamic dispersion coefficient $\left(D\right)$ and the retardation factor $\left(R_d\right)$ are investigated. The significant factors considered are the curing period, seepage velocity $\left(v\right)$ , reference concentration $\left(C_R\right)$ , and mean particle size $\left(d_{50}\right)$ . Other factors such as porosity $\left(n\right)$ and mix design are also discussed. Results show that a longer curing period lowers all three transport parameters. Furthermore, as the seepage velocity increases, $R_d$ decreases and $D$ increases. The yielding velocity at which mechanical dispersion $\left(D_{\mathrm{md}}\right)$ starts prevailing is observed at about $0.0001\mathrm{cm}∕\mathrm{s}$ . Both $R_d$ and $D$ are seen to reduce with increasing $C_R$ . Thus, the concept of $C_R$ could be used to explain the data scattering in a CB hydrodynamic curve.