Concrete with flash-calcined dredging sediments as a novel supplementary cementitious material

Maintenance dredging in the port of Antwerp annually generates about 450.000 tons of dry matter sediment, for which suitable disposal solutions or applications are required. Mechanical dewatering of the sediments results in filter cakes, comprising clays (2:1 clay minerals and kaolinite), quartz, calcite and an amorphous phase as major mineral phases. Flash calcination of these filter cakes reduces the total organic carbon fraction and results in a dehydroxylation of the clay minerals. Isothermal conduction calorimetry tests demonstrated the pozzolanic reactivity of the calcined material, being superior to that of a siliceous fly ash. As a result of the pozzolanic reactions, replacing 20, 30 or 40 wt.% of cement by calcined dredging sediments leads to a strength development equivalent to a reference mix with Portland cement up to 28 days, despite low strength at early age. This paper presents material characteristics and pozzolanic reactivity of the flash-calcined dredging sediments, as well as their effect on setting time, fresh concrete properties and mechanical characteristics. The initial results clearly show that the flash-calcined clay-rich dredging sediments have great potential to be used as a novel pozzolanic supplementary cementitious material, for the production of sustainable, low-CO2 blended cements and concrete.status: publishe