Geo-characterisation of lime water treatment sludge

In-situ and laboratory tests were performed on lime sludge generated from a drinking water-softening process and disposed of in a sedimentation lagoon. The sludge consists predominantly of calcite. It is poorly graded, low-plasticity silt with in-situ w(c) around 70%, gamma(t) around 15 kN/m(3) and e between 1.5 and 2.5. The optimum w(c) for standard and modified Proctor compaction is 30% and the maximum gamma(d) values are 12 and 13.5 kN/m(3) respectively. The C-c and C-r for undisturbed sludge specimens are 0.54-0.68 and 0.021-0.046. C-v and k decrease with increasing vertical stress. The disposed sludge is sensitive and the in-situ S-u,S-max varies with depth. Stratification of the sludge is evident by the varying values of in-situ S-u,S-max, S-u,S-r and S-t with depth and V-s profiles. Potential engineering reuse options for the sludge are buffer for acidic soil and low-permeability fill for landfills and brownfields, as well as engineering fill. The properties of lime sludge are different from those of coagulation sludge, primarily due to their different chemical compositions. Coagulation sludge has the physical characteristics of high-plasticity clay. Consequently, lime sludge shows comparatively higher gamma(d), lower C-c and C-r and higher C-v than coagulation sludge.