Admixtures or supplementary cementitious materials are generally characterised by their ability to react in specified conditions. This can be assumed through the pozzolanicity. In this study, the pozzolanic activity of a certain category of materials was investigated. For this purpose, the Frattini test conforming to NF EN 196-5 French standard, the accelerated Chapelle test, the measurement of the electrical conductivity and the calculation of mechanical activity coefficient were performed. The raw sediment from Dunkirk harbour presented a relatively low pozzolanic activity regardless of the test considered. However, the study of direct or flash calcined materials evidenced that sediment acquired at the end of these processes an improvement of pozzolanic activity. The comparative study conducted on several common admixtures also inferred that the Chapelle and mechanical activity index methods are quite appropriate and reliable. Nevertheless, in the conductivity test, a correction must be applied due to the presence of dissolved salts. A mechanical activity coefficient of χA = 0.88 and χA = 0.73 was determined for STFC (flash) and STDC (direct lab kiln) respectively. As a result, sediment, following an optimized treatment can be used as active mineral admixture in cementitious matrixes. © 2017 Elsevier B.V.