The assessment of cementitious additives used for the stabilisation/solidification of dredged harbour sediments.

This research examined the use of cementitious additives to physically and chemically stabilise dredged harbour sediments for use as fill or for land reclamation purposes. Different combinations of Cement, Stabilime, Old Cement Kiln Dust (OCKD) Diatomite and Amorphous Silica additives were used to stabilise fine dredged harbour sediments from the Nelson and Bayswater (Auckland) marina developements. The relative performance of these different additive combinations were measured in terms of unconfined compressive strength (UCS), and their ability to bind metals using the TCLP leach test. These results were then compared with those obtained using only lime or cement as the additive. This research showed that the two sediments behaved quite differently. This was predominantly due to differences in their clay content and mineralogy. Ofthe different additives, a combination of stabilime and diatomite at a ratio of 75/25 gave best strength results for the Bayswater sediment. Nelson sediment was best stabilised using cement, however, significant substitution of cement with OCKD was shown to be possible without large strength losses. Leaching of zinc, copper, lead, chromium, nickel and cadmium was measured using the TCLP leach test. For the majority of formulations tested, levels of metals leached were found to be less than 10% of their original total content. A link between the final leachate pH and the percentage of each metal leached was the most significant trend identified from the TCLP leach tests. This indicated that precipitation as hydroxides and other similar exchangeable compounds is one of the primary mechanisms binding these metals. The results from this research cannot be used directly in other applications; however, the procedures and methodologies outlined, and the conclusions that have been made, provide a good starting point for identifying a suitable additive for a particular sediment solidification/stabilisation application