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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.

This paper focuses on the causes and consequences of early-age cracking of mass concrete foundation slabs due to restrained volume changes. Considering the importance of water leaking through cracks in terms of the serviceability, durability and environmental impact of watertight concrete structures, emphasis is placed on the effect of temperature loads on foundation slabs. Foundation slabs are usually restrained to some degree externally or internally. To evaluate the effect of external restraints on foundation slabs, friction and interaction models are introduced. The reinforcement of concrete cannot prevent the initiation of cracking, but when cracking has occurred, it may act to reduce the spacing and width of cracks. According to EN 1992-1-1, results of calculating crack widths with local variations included in National Annexes (NAs) vary considerably. A comparison of the required reinforcement areas according to different NAs is presented.