# Effects of Short Fibers on the Long-Term Behavior of RC/FRC Beams Aged under Service Loading
## 4 Conclusions  
In the present paper, the results of an extensive experimental campaign with the aim of investigating the beneficial effects of short (steel and polyester) fibers in FRC beams under sustained loads are presented and discussed with special attention to long-term behavior and durability. Fibers were used as additional reinforcement to rebars present in all of the beams, and designed according to Eurocode 2. Ten Reinforced Concrete (RC) beams were monitored for several months during exposure to natural agents under sustained (service) load. In addition, three reference RC/FRC beams (made of the same materials) were tested 28 days after casting without any environmental exposure (Set #1). After long-term loading and exposure (17 months for Set #2 and 72 months for Set #3), all of the beams were unloaded and tested in the laboratory under monotonic conditions up to failure. Experimental results confirm that fiber reinforcement helps in reducing crack width and in increasing the flexural stiffness of the FRC beams. In fact, long term loading provokes an increase of deformations that corresponds to a stiffness loss which was particularly evident in PC beams. The FRC beams with steel fibers showed the highest flexural strength. The use of FRC (in addition to conventional reinforcement) allows for a reduction of the crack width of up to 50%. In particular, up to the service load (about 50-60 kN), polyester FRC beams have shown lower values of mean crack width, compared to steel FRC beams. However, FRC beams with steel fibers showed the maximum flexural strength (due to the highest fracture energy of FRC). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Beam ID Tag** & **T (Months)** & **Beam ID Tag** & **T (Months)** \\ \hline PC\_E\_72 & 61.0 & PC\_E\_17 & 28.8 \\ ST1\_E\_72 & 64.0 & ST1\_E\_17 & 67.1 \\ ST2\_E\_72 & 85.2 & ST2\_E\_17 & 60.0 \\ POL1\_E\_72 & 64.3 & POL1\_E\_17 & 69.2 \\ POL2\_E\_72 & 85.9 & POL2\_E\_17 & 68.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Estimated time for the start of corrosion in exposed beams (17 and 72 months). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Beam ID**} & \multicolumn{2}{c}{**K (mm/year\({}^{\mathbf{0.5}}\))**} & \multicolumn{2}{c}{**K (mm/year\({}^{\mathbf{0.5}}\))**} \\ \cline{2-5}  & **Un Cracked** & **Cracked** & **Tag** & **Un Cracked** & **Cracked** \\
**Tag** & **Sections** & **Sections** & **Sections** & **Sections** \\ \hline PC\_E\_72 & 6.77 & 13.30 & PC\_E\_17 & 8.07 & 19.38 \\ ST1\_E\_72 & 10.46 & 12.99 & ST1\_E\_17 & 8.46 & 12.69 \\ ST2\_E\_72 & 11.42 & 11.26 & ST2\_E\_17 & 8.18 & 13.44 \\ POL1\_E\_72 & 8.70 & 12.96 & POL1\_E\_17 & 9.11 & 12.49 \\ POL2\_E\_72 & 9.97 & 11.21 & POL2\_E\_17 & 9.05 & 12.58 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Carbonation coefficients in exposed beams: 17 vs. 72 months. Furthermore, FRC led to an enhanced ductility in structural members (especially in beams with steel fibers) and to smaller mid-span deflections. The beneficial effect of fibers has been studied also in terms of durability. In fact, FRC beams have shown a lower crack width and, therefore, a lower carbonation depth at the cracked sections (than do the PC beams). However, in uncracked sections the carbonation depth of the FRC beams was slightly higher than that in the PC beams, probably due to the higher porosity of the matrix provoked by the reduced workability of FRC. Finally, the experimental results of the long-term bending tests clearly show the beneficial effects from FRC; such properties make FRC a suitable material for improving the service life performance of reinforced concrete structures. Conceptualization, G.P., M.A.A. and F.M. ; methodology, G.P., M.A.A., F.M. and E.V. ; investigation, E.V., L.C., F.M. ; data curation, E.V. and L.C. ; writing--review and editing, F.M., E.V., L.C. ; supervision, G.P. and M.A.A. ; project administration G.P. and M.A.A. This research received no external funding.