# Effects of Short Fibers on the Long-Term Behavior of RC/FRC Beams Aged under Service Loading
## 3 Experimental Results and Discussion
### Long-Term Behavior
#### 3.1.3. Durability Tests  
After carrying out the mechanical tests, the beams were cut both along the cross and longitudinal directions in order to perform durability tests. Firstly, ion chloride penetration was checked in cross sections by means of a colorimetric test based on a sprayed solution of silver nitrate (AgNO3). No reaction displaying a violet color was assessed by infrared light, not even after alkalizing the surfaces. Therefore, according to [PERSON] et al. [44], it is likely that the chloride content is lower than 0.012% of the concrete weight; for this reason, it can be considered negligible.  
Carbonation depth was checked at both cracked and uncracked sections, leading to interesting, and somehow apparently controversial, results. Table 4 reports the mean carbonation depth values obtained from measurements taken on both sides of the longitudinal sections for each single beam exposed for 72 months. The mentioned mean values refer to the measurements taken respectively at all cracked sections along the constant moment zone and in 12 points of the uncracked area. FRC beams showed lower crack widths and slightly lower carbonation depths in cracked sections than the PC beams. However, in uncracked sections the carbonation depth in the FRC beams is slightly greater than in those PC beams; this is probably due to the increased porosity of FRCs, which show a higher content of entrapped air in the mold than the PC mix [45]. The increased content of entrapped air is a consequence of the reduced workability of FRC, and is considered the main cause of the slightly reduced compressive strength of FRC (Table 2). This clearly evidences that a proper mix design becomes a major issue in FRC in order to avoid reduced workability and a consequent increase of porosity.  
The carbonation depth \(D\) (measured in mm) in uncracked concrete sections can be determined by means of the well-known [PERSON]'s formula \(D=K\times t^{0.5}\), where \(K\) is the carbonation coefficient  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Uncracked Sections**} & \multicolumn{2}{c}{**Cracked Sections**} \\ \hline \multirow{2}{*}{**Beam ID**} & **Carbonation** & \multirow{2}{*}{**Standard**} & **Carbonation** & **Standard** & **Maximum** \\  & **Depth** & **Deviation** & **Depth** & **Deviation** & **Carbonation** \\ \cline{1-1}  & **(mm)** & **Deviation** & **(mm)** & **Deviation** & **Depth** \\ \hline PC\_E\_72 & 16.59 & 3.30 & 33.82 & 10.41 & 49.13 \\ ST1\_E\_72 & 25.63 & 2.68 & 31.81 & 8.33 & 45.16 \\ ST2\_E\_72 & 27.97 & 3.04 & 27.59 & 4.41 & 34.02 \\ POL1\_E\_72 & 21.31 & 3.06 & 30.61 & 4.77 & 37.44 \\ POL2\_E\_72 & 24.41 & 1.44 & 26.55 & 6.93 & 36.18 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Carbonation depths and standard deviation for 72-month exposed beams.  
Figure 7: Carbonation depth and standard deviation for 72-month exposed beams.  
and \(t\) is the time in years [46]. Taking into account the exposure time and the carbonation depths reported in Table 4, the \(K\) coefficients for each exposed beam can be obtained, as reported in Table 5; results confirm the observation reported in [23]: Carbonation agents penetrate faster into cracks than in uncracked concrete, and carbonation coefficients are lower for FRC compared to PC. It can be noticed that the values of coefficients \(K\) are similar between beams with same mix exposed, respectively for 17 and 72 months (except for PC_E_72, which had a K value in cracked sections 30% lower than that of PC_E_17). Figure 7 shows the average values of the carbonation depth, as measured in the beams of Set #3 after 72 months of exposure.  
The application of [PERSON]'s formula provides the predictions of the time to the start of corrosion (in months) for the tested beams (Table 6); however, it should be underlined that the load level applied in the long-term tests (50 kN) was higher than the quasi-permanent load assumed by EC-2 [24].