## 1 Introduction  
A high sulfate concentration and low pH value of wastewater are suitable for the growth of sulfur-oxidizing bacteria, which produce sulfuric acid, making the reinforced concrete drainage pipes within a wastewater environment susceptible to long-term acid corrosion [1]. Reinforced concrete pipes then crack and spall, causing a gradual reduction in their wall thickness due to corrosion, which decreases the bearing capacity of the pipes and can potentially cause structural fail; therefore, timely repair of reinforced concrete pipes is necessary [2]. The spray construction method, originally used as a repair technology for steel pipes via manual application, aims to stop further corrosion of internal pipe walls. In 1933, American company Centriline introduced the cement mortar spray construction restoration technique, which utilizes machinery for mortar spraying and is commonly referred to as the Centriline technique. In 1934, the city of Newark, NJ, USA, employed the spray construction method to repair an 8.4 km section of a steel pipe, solving the problem of leakage and improving the flow capacity of the original pipeline [3]. In 2003, during the renovation of the Shanghai Yang Shupu water plant outlet pipe, it was determined that the pipe has been initially repaired with cement mortar during its construction [4]. Scholars around the world have researched the coordinated deformation relationship between the lining and existing pipelines. [PERSON] analyzed the concrete pipe-liner-mortar layer relationship and concluded that the three are completely bonded; that is, the composite structure, and the three as a whole, bear the load together [5]. [PERSON] determined that when the coordinated deformation of the existing pipeline lining depends on the relationship between the load on the interface and the interface resistance, and if the resistance is greater than the load, the two form a superimposed composite structure. An indoor test of the composite structure model indicated that the bearing capacity of the upper and lower beams could not be fully exerted due to the gap caused by the shrinkage of the mortar layer, which was approximately 0.6-0.9 times the theoretical value [6]. WRC studied the influence of the modulus of the mortar layer on the bearing capacity of the repaired pipeline. It was found that the deformation of the lining pipe was 0.16% and 0.08% at 8 and 12 MPa, respectively, while deformation without lining was 0.56%. The contribution of the mortar layer to the bearing capacity of the repaired pipeline was higher than that of the pipeline lining [7]. [PERSON] et al. studied the influence of the lining thickness, deformation degree, and reinforcement ratio on the bearing capacity of existing pipelines based on a trilateral load test of mortar-repaired reinforced concrete pipelines [8]. Most existing theories regard the lining layer and the existing pipeline as primary force structures, though the interface between the lining layer and the pipeline may be detached under an external load. However, there is a lack of research on the overall mechanical properties of reinforced concrete composite members under corrosion conditions [9]. In this paper, the residual bearing capacity of reinforced concrete pipes with different degrees of corrosion was simulated, and the variation law of the residual bearing capacity of reinforced concrete pipes was studied using a ring stiffness instrument loading test. Ultra-high-performance concrete materials were used to repair the corroded and thinned reinforced concrete pipes, and three parameters were set up, including different corrosion and repair thicknesses and different interface forms. The control variable method was used to study the influence of each parameter on the bearing capacity of reinforced concrete pipes, and the applicability of ultra-high-performance concrete material as a spray repair material was analyzed.