## 2 Materials and Experimental Procedure
### Microstructural Study and Performance Testing  
Here, CAD software was used to measure the cladding thickness of the reinforcement bars. First, a DFK 38 GX267 camera was used to capture images of the end and shaft faces of the clad rebars; these images were imported into CAD, and the cladding thicknesses of the rebars were measured using the CAD annotation tool.  
Sandpaper and a metallographic polishing flannel were used to grind and polish the rebar until both the stainless and carbon steels reached the leaching standard. Afterwards, an ethanolic solution of nitric acid (4%) was used to corrode the carbon steel side, and the mixed reagents with a volume ration of HNO\({}_{3}\):HCL\({}_{3}\):H\({}_{2}\)O = 1:3:4 were applied to corrode the stainless steel side. Finally, the corroded specimen was placed under a BH200M optical microscope for observation.  
Microscope specimens \(\approx\)4 um in length and 50 nm in thickness were prepared using the focused ion beam technique, and the microstructure at the composite interface was observed using transmission electron microscopy (TEM, Talos \(\mathrm{f200}\times\), Thermo Fisher Scientific, Waltham, MA, USA) at an accelerating voltage of 5 kV and a beam-shift current of 0.8 nA. The elemental distribution on both sides of the composite interface was analysed using an EPMA-8050G electron probe (Shimadzu, Tokyo, Japan). A HVT-10Z Vickers hardness tester (Jinan Huayin Test Instrument Co., Jinan, Shandong, China) was used to test the microhardness of the composite interface, where the test load was 0.5 kg. A HUT106A universal testing machine (Shenzhen Wance Testing Machine Co., Shenzhen, Guangdong, China) was used to test the tensile properties of the clad rebars; the tensile rate was 2 mm/min. After the tensile test, the tensile fractures of the clad rebars were manually saved off, and the microscopic morphology of the tensile fractures was observed using a TESCAN VEGA3 scanning electron microscope (Tescan, Brno, South Moravia, Czech Republic). A ZFWY-50 bending tester (Shanghai Bairoe Test Instrument Co., Pudong New Area, Shanghai, China) was used to test the bending performance of the clad rebar. After the bending test, the specimen was cut in half using a wire cutter and inspected to determine if the base cladding had become detached.  
Salt spray corrosion testing was performed on the rebars using a LYW-075 salt spray corrosion chamber (Shanghai Yiheng Technology Instrument Co., Fengxian, Shanghai, China) according to ISO 9227-2017 and the following experimental parameters: corrosion medium, 5% NaCl solution; solution pH, 6.8-7.2; corrosion chamber temperature, 35 \({}^{\circ}\)C; and spray volume 1.5-2.5 mL/(90 cm\({}^{2}\) h). After the corrosion experiment, the surface of the reinforcement was descaded according to ISO 8407-2009. The descaling solution  
Figure 6: Schematic of the cut end of a composite billet.  
parameters are listed in Table 3. The surface area of the rebar was determined using an ATOS optical scanner (Daum Optical Technology Co., Lower Saxony, Brunswick, Germany) and ScanBox software.  
Figure 7 shows is a schematic of the shear jig. The bond strength of the clad rebar was tested by cutting it into the specified size, placing it into a shear jig and locking it in place. Then, the shear jig was placed under a HUT106A universal testing machine, with the indenter of the tester driving the trapezoidal slider downwards to ensure shearing of the stainless steel from the carbon steel base. Finally, the bond strength of the clad rebar was calculated from the shear force.