## 2 FRC Under Chloride Ingress
### Impact of Fibres on Chloride Ingress in Concrete  
Several authors, including [PERSON] et al. (2018), [PERSON] et al. (2018), [PERSON] et al. (2018), [PERSON] and [PERSON] (2018), [PERSON] et al. (2018), have performed extensive literature reviews on the durability aspects of different types of FRC. Focusing exclusively on findings related to chloride-induced corrosion and incorporating insights from more recent studies, a summary table of key conclusions from previous research is provided below (Table 1). The table serves as a basis for evaluating the performance of RR-FRC elements in the following chapter. Unless otherwise noted, the crack width values (\(w\)) refer to widths to which the elements were pre-cracked. Fibres themselves may also be susceptible to corrosion depending on their composition. On the one hand, steel fibres (SF) have been found to be prone to corrosion according to [PERSON] et al. (2018); however, the study's authors observed that their corrosion resistance was higher compared to rebar and attributed this enhanced resistance to the presence of mill scale on the fibre surface. [PERSON] (2018) offered an alternative explanation, suggesting that the increased resistance to chlorides of SF might result from their production process. [PERSON] et al. (2018) identified a linear relationship between the duration of SF exposure to sodium chloride (NaCl) and the reduction in fibre diameter. They also observed that the corrosion rate of SF is affected by pH levels, with higher pH values (above 12) resulting in a very slow corrosion rate. This finding underscored that the corrosion of SF is governed by the same fundamental mechanism as the corrosion of rebar. [PERSON] and [PERSON] (2018) found that coating SF in triethanolamine (TEA) is an efficient method to increase their resistance to corrosion. [PERSON] et al. (2018) observed an increase in the bond strength of corroded SF on account of the increased surface roughness of corroded fibres. On the other hand, [PERSON] and [PERSON] (2018) compiled a comprehensive report on the chemical resistance of thermoplastic materials. Based on it, polyethylene and polypropylene as materials have excellent resistance to seawater and NaCl exposure at various temperatures. This implies that polypropylene fibres (PPF) and polyethylene fibres (PEF) themselves are immune to chloride attack. This claim is further supported by the results of a review by [PERSON] et al. (2018) on the use of polyolefin (PPF, PEF) in the construction industry. \begin{table}
\begin{tabular}{l l l l l l l l l} \hline \hline
**Paper** & \(w\)/\(b\) & \begin{tabular}{l} **Duration** \\ **[d]** \\ \end{tabular} & **Material** & \(\begin{tabular}{l} \(V_{\ell}\) \\ **[\%]** \\ \end{tabular} & \
\begin{tabular}{l} **NaCl** \\ **[\%]** \\ \end{tabular} & \(
\begin{tabular}{l} \(w\) \\ **[mm]** \\ \end{tabular} & \multicolumn{3}{c}{**Conclusion**} \\ \hline
[43] & 0.30 & 91 & \begin{tabular}{l} MSFRC, \\ SFRC, \\ HyFRC 1 \\ \end{tabular} & SF: & 0.25–1.00, & 10.0 & 0.00 & 0.00 & - & SF reduce water absorption with the increase in \(V_{\ell}\) \\  & & & \
\begin{tabular}{l} PFF: \\ 0.15–0.45 \\ \end{tabular} & 0.10–0.00 & 10.00 & 0.00 & 0.00 & - &
\begin{tabular}{l} PFF increase porosity; \\ - \\ \end{tabular} \\ \hline
[44] & 0.31 & - & PC, SFRC & SF: 0.76 & 10.0 & 0.00 & - &
\begin{tabular}{l} Similar water absorption of PC and SFRC; \\ - \\ \end{tabular} \\  & & & & & & & \\ SF reduce electrical resistivity of concrete by 63\%. & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Experimental setups and concrete properties considered in the reviewed campaigns regarding FRC. The results from studies reviewed in Table 1 predominantly point to increased water tightness, lower permeability and lower chloride penetration in FRC elements compared to PC, with benefits correlating with an increase in the fibre content, regardless of fibre type.