Significant volumes of sediment are annually dredged in France and all over the world and these materials may in fact be used beneficially as supplementary cementitious material. This paper studies the durability of a new cement matrix based on dredged marine sediment from the Dunkirk-Harbour (northern France). Several techniques are used to characterise the raw sediment, such as physical properties, chemical analyses and mineralogy. X-Ray Diffraction (XRD) analysis revealed quartz, calcite and kaolinite to be the main mineral phases. In order to eliminate organic matter and activate some of those minerals, the sediment is calcined at a temperature of 850 °C for 1 h. Moreover, four blended mortars were formulated by mixing a portland cement (CEM I 52,5 N) and the calcined sediment as a partial cement substitute (0%, 10%, 20% and 30%). Reference mortars, based on the blended cement, were then prepared. This re-use cannot be substantiated or efficient without a durability study. For this purpose, the following tests were conducted on those mortars: mercury porosity, accessible water porosity, chloride permeability, freezing and thawing, external sulphate attack, alkali aggregates reaction, compressive and bending strength tests. The results of most of those tests evidenced the fact that the mortar that contains 10% of the treated sediment is as efficient and durable as the reference mortar itself. This infers that the presence of these calcined sediments improves the general behaviour of mortar.