This paper presents a theoretical and experimental work aiming at understanding the mechanical behaviour of Bituminized Waste Product (BWP). This material is considered for this purpose as a mixture of bitumen and crystals of sodium nitrate. For BWP, both bitumen and crystals contribute to the creep deformations. In this study, an attempt is made to develop an elasto-viscoplastic model that describes the creep behaviour of BWP considering the constituents’ creep behaviour. An experimental program has been set up to get insight in the material response. The elasto-viscoplastic constitutive model has been implemented into a finite element program. The modelling results have been compared with the experimental data.