Solidification of New Zealand Harbor Sediments Using Cementitious Materials

Dredged harbor sediments contaminated with harmful industrial chemicals need to be physically and chemically stabilized before being used in harbor developments. Solidification is often done using cement or lime additions but the performance of these materials is affected by the type and content of clay in the sediments. Two New Zealand harbor sediments, containing 18–27% clay and moderate levels of heavy metals, were investigated as part of marina developments in Nelson and Auckland harbors. Binding of these sediments was investigated using Portland cement, cement kiln dust, lime, amorphous silica, and diatomite. The effectiveness of physical binding of these systems was found to be dependent on the clay type, with montmorillonite clays producing higher compressive strength than kaolinite clays (cf. highest strengths of 1,320 and 630 kPa, respectively). Research findings indicate that effective solidification of contaminated harbor sediments is possible using a range of materials including waste products from the cement industry such as cement kiln dust that produced strengths of almost 800 kPa.