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Although fiber-reinforced polymers (FRPs) have achieved increasing popularity in strengthening concrete structures and reinforcing new ones, there is to date insufficient knowledge about their long-term behavior. The long-term properties of FRPs specified in design codes lead to the low utilization capacity of these materials and are not supposed to be correct according to the actual behavior of structures reinforced with FRPs after 20 or 30 years of their use. Environmental impact reduction factors limit the mechanical properties of FRP composites in a range from 0.95 for CFRP to 0.5 for GFRP; the creep rupture factor is from 0.9 to 0.2. The paper summarizes previous research and experimental studies on the long-term properties of FRP reinforcements and also their comparison with the actual structures in which this reinforcement has been used; it presents the first part of an experimental investigation with comparative calculations. [ABSTRACT FROM AUTHOR]