The effectiveness of using siliceous-aluminous fly ash and cement in solidifying Dunkirk marine sediments was investigated by means of laboratory tests to evaluate the compatibility of solidified material as roadbed materials. For this purpose, the mechanical properties of various designed mixes were investigated by the modified Proctor compaction tests, the tensile strength tests and the unconfined compressive strength tests. The swelling properties and bearing capacity changes were studied under water immersion condition for 4 days by standardized swelling test. For evaluating the impact of freezing-thawing cycles and water immersion damage on strength properties of cement/fly ash-sediment mixes, 20-cycle freezing-thawing tests and 32-day water immersion tests were realized on standard cured cylindrical samples. A coefficient of strength loss was defined to quantify the effect of freezing-thawing damage and water immersion aging on durability of designed mixes. XRD tests were carried out to verify the formation of cementitous compounds CSH and highlight the chemical transformation in sediments. The techniques help explain the change in mechanical properties of cement/fly ash-based sediments. (C) 2012 Elsevier Ltd. All rights reserved.