The main aim of the paper was to assess whether the lightweight concrete with a new type of sintered fly ash aggregate can be used as a structural material for post-tensioned elements subject to high effort. This purpose was achieved by comparison of the properties of lightweight aggregate concrete with Certyd aggregate (LWAC) and normal-weight concrete with dolomite aggregate (NWAC) of similar strength in terms of their suitability for use in prestressed members. Special emphasis was placed on long-term, relatively rarely performed tests of rheological properties such as shrinkage and creep. The research was conducted on standard specimens as well as on plain and post-tensioned beams of bigger scale, which could reflect better the behavior of the materials in a destined type of structural members. The carried out tests showed that, despite the expected lower density and modulus of elasticity, LWAC revealed comparable tensile strength and lower shrinkage and creep in the whole time of observations (ca 1.5 years) in comparison to NWAC. Moreover, the total loss of prestressing force for beams made of LWAC was slightly lower than for NWAC. Estimations of tensile strength and modulus of elasticity values according to the standard Eurocode EN-1992-1-1 for both concrete types turned out to be satisfactory. However, the rheological properties of the tested lightweight concrete seemed to be considerably overestimated.