## 3 Results and Discussion
### Analysis of Clad Rebar Corrosion-Resistance  
To effectively evaluate the corrosion resistance of the clad rebars, we selected clad rebars, epoxy-resin rebars, galvanised rebars, carbon rebars, and 316L stainless steel round bars (stainless steel round bars were used instead as stainless steel rebars could not be sourced commercially) for the salt spray corrosion experiments; the rebar dimensions were \(\Phi 25\times 500\) mm. The corrosion time was 42 d; every 7 d, a set of specimens was removed and analysed. The ends of the clad rebars were weld-sealed before the corrosion experiments were initiated. Figure 19 shows the surface morphology of each specimen before corrosion.  
Figure 20 shows the surface morphology of each specimen after corrosion. As can be seen from the diagram, a rust layer was visible on the surface of the carbon reinforcement after 7 days of corrosion. After 21 days of corrosion, the horizontal and vertical ribs of the carbon rebars disappeared. Epoxy reinforcement did not change significantly in the early stages of corrosion but, as the corrosion progressed, the resin at the ends of the cladding began to fall off, and corrosion products were gradually deposited.  
Figure 19: Surface morphology of each specimen before corrosion.  
Figure 18: Schematic of corrosion depths on reinforcement ends: (**a**) epoxy seals; (**b**) sleeve joints; (**c**) without sealing treatment; (**d**) welded seals.  
Compared with the corrosion of the epoxy rebar, the galvanised rebar corrosion was more serious. After 7 d, the galvanised layer of the rebar peeled off in a large area, and after 14 d, a large amount of yellow rust appeared on the surface of the rebar. After 35 d, the galvanised layer on the surface of the rebar disappeared; at this point, the surface morphology of the galvanised rebar was similar to that of the carbon steel. In stark contrast to the other rebars, both the 316L stainless steel round bar and clad rebars demonstrated good corrosion resistance, without any obvious pitting or cracking of their surfaces during the corrosion process.  
At the end of the corrosion experiment, the rebars were de-rusted, dried, and weighed, and the corrosion rate for each rebar was calculated using Equation (3), as follows:  
\[R=\frac{G_{0}-G_{1}}{S\cdot t}\times 10^{6} \tag{3}\]  
where \(R\) is the weight-loss rate of the reinforcement, g/(m\({}^{2}\) h), \(G_{0}\) is the mass (g) of the reinforcement before corrosion, \(G_{1}\) is the mass (g) of the reinforcement after rust removal, \(S\) is the surface area (mm\({}^{2}\)) of the reinforcement, and \(t\) is the corrosion time (h).  
Figure 21 shows the corrosion rate curves of the rebars. As can be seen, the corrosion rates of the carbon rebars and galvanised rebars increase and then decrease as the corrosion time increases. The reason for this is that, at the later stage of the corrosion, the rust layer of the rebars can effectively isolate the contact between the corrosive medium and the substrate, so as to slow down the process of corrosion. A comparison between the clad rebars and the stainless steel round bars shows that the variation curves almost coincide, indicating that the corrosion resistance of the clad rebars is similar to that of the stainless steel round bars. The corrosion rates of the rebars decrease in the following order: carbon rebar > galvanised rebar > epoxy rebar > clad rebar > stainless steel round bar. The corrosion rates for the carbon reinforcement and clad rebar are \(\approx\)2.2 g/(m\({}^{2}\) h) and \(\approx\)0.22 g/(m\({}^{2}\) h), respectively, a difference of 10-fold.  
Figure 20: Surface profile of each specimen after various corrosion times: (**a**) 7 d; (**b**) 14 d; (**c**) 21 d; (**d**) 28 d; (**e**) 35 d; (**f**) 42 d.