## 3 RR-FRC Under Chloride Ingress
### Corrosion Initiation and Corrosion Propagation in RR-FRC
#### 3.1.1 Effects of Cracks on Corrosion Initiation and Propagation
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corrosion initiation time based on measurements of corrosion potential (\(E_{\text{corr}}\)) and the rebar weight loss determined by corrosion current density (\(i_{\text{corr}}\)) are plotted for different concrete types (summarised in Table 2). The influence of cracking conditions is clear (Figure 1), as uncracked elements consistently remained passive for over 30 weeks, whereas cracked elements with \(w\) between 0.06 and 0.10 mm experienced nearly instantaneous corrosion initiation. [PERSON] et al. [81] investigated non-loaded and loaded (in pure axial tension) RC and RR-HyFRC elements. An axial tensile load of 53 kN was used to pre-crack specimens (resulting in a tensile stress of 265 MPa in the reinforcement, which is below the threshold value for SLS given in EC2 [25]). The resulting maximal crack widths from axial loads equalled 0.42 mm for RC and 0.22 mm for RR-HyFRC. The effect of fibres on the crack widths can be clearly seen in Figure 2. In ascending order, the time of corrosion initiation was observed after 35 days (loaded RC), 35 days (loaded RR-HyFRC), 301-401 days (non-loaded RC) and 511-681 days (non-loaded RR-HyFRC). In the propagation phase, the same trend was observed, with higher values of \(i_{\text{corr}}\) in RC than in RR-HyFRC. This study also used accelerated corrosion with wet/dry cycles (2 weeks per cycle) for 912 days, similar to studies by [PERSON] et al. [79; 80]. In the campaign by [PERSON] et al. [83], the elements were cyclically loaded in 4 PBT (five cycles) up to 42 kN to simulate SLS conditions while maintaining the reinforcement  
Figure 1: (**a**) Rebar weight loss under chloride attack; (**b**) Corrosion initiation time (PL refers to RC, ST to RR-SFRC, SY to RR-PVAFRC, Hy to RR-HyFRC) [80]. Figure 2: Tensile cracks in (**a**) RC; (**b**) RR-HyFRC [81]. in the elastic range. This resulted in cracks opening in RC elements, whereas RR-HyFRC remained uncracked. Electrochemical measurements indicated that the corrosion process began in RC elements within the first week of exposure, whereas corrosion initiation in RR-HyFRC was only observed after six weeks. The average loss of reinforcement mass due to corrosion was 0.132 g/cm\({}^{2}\) for RC and 0.039 g/cm\({}^{2}\) for RR-HyFRC elements. In Figure 3, higher degradation of rebar in the case of RC may be observed. This correlates with the percentage of reinforcement surface area covered by corrosion products, averaging 93% for RC and 26% for RR-HyFRC. In the study by [PERSON] et al. [84], a methodology similar to the one in [83] was used (five loading cycles up to 32 kN in 4 PBT were used to pre-crack specimens). After one year, the chloride solution was allowed to evaporate, and corrosion monitoring was continued in dry conditions. Corrosion initiation was fastest in pre-cracked RC specimens (one week), followed by uncracked RC specimens (five weeks). For the first 45 weeks of exposure, no active corrosion process was detected in either uncracked or cracked RR-HyFRC elements. An active corrosion process in the top bars of RR-HyFRC specimens was only detected in the second year of the campaign. In RC elements, cracks formed due to active corrosion, whereas RR-HyFRC remained uncracked. In cracked RC elements, previously induced cracks grew in size and depth, allowing the chloride solution to reach the bottom bar (Figure 4) and initiate the corrosion process. The highest measured value of \(i_{\text{corr}}\) was recorded for the cracked RC element, amounting to 21.95 \(\upmu\)A/cm\({}^{2}\) (bottom bar) and 6.05 \(\upmu\)A/cm\({}^{2}\) (top bar). In the uncracked RC element, the bottom bar remained in a passive state, whereas the \(i_{\text{corr}}\) for the top bar was 2.80 \(\upmu\)A/cm\({}^{2}\). For the RR-HyFRC elements, similar values of \(i_{\text{corr}}\) were observed for the top bars: 0.43 \(\upmu\)A/cm\({}^{2}\) for the un-damaged elements and 0.40 \(\upmu\)A/cm\({}^{2}\) for the pre-cracked elements. The bottom bars of both RR-HyFRC elements remained in a passive state.