During the last two decades, low cost Fe-Mn-Si based shape memory alloys have attracted much attention in the research community and practice, as a cost-effective alternative to the expensive Ni-Ti based shape memory alloys. A shape memory alloy (SMA) has the unique property to remember its initially given shape after being deformed. The reason is that its crystal transformation is reversible. Empa and Company re-fer developed an iron based shape memory alloy (Fe-SMA), also denominated as 'memory-steel'. The Fe-SMA can be used as near surface mounted NSM strengthening reinforcement. The NSM Fe-SMAs can more easily be prestressed than NSM FRP, because prestressing of SMAs does not require any mechanical jacks and anchor heads. This practice requires cutting grooves in the cover of the concrete and no surface preparation work is needed afterwards.
When NSM Fe-SMAs are used for the strengthening of concrete structure, one critical aspect that needs to be investigated is the long-term behavior of such applications. The current paper presents an experimental investigation to determine the long-term behavior of strengthened RC beams under sustained loading in an outdoor exposure environment using an older prototype of Fe-SMA elements. Two beams strengthened with NSM ripped Fe-SMA strips, one with activated Fe-SMA strips and one with not-activated Fe-SMA strips, have been loaded until more than their cracking loads and their behavior has been monitored for about four years. Results show that both beams have similar trends in their mid-span deflection measurements, what indicates a stable prestressing force in the Fe-SMA strips.