As an efficient means of underground engineering construction, wet spraying technology of concrete is widely used in tunnel construction. However, how to effectively reduce the rebound rate of concrete and improve the quality and economy of operation has always been the focus of the industry. This article will explore how to effectively control the rebound of concrete by combining refined management with operating skills.

　　1. Strict quality control of raw material selection

　　All raw materials used for wet spraying must be strictly tested to ensure that they meet engineering standards. In particular, key additives such as accelerators must be properly stored to avoid performance degradation due to moisture, which affects the quality of the final concrete.

　　2. Accurately control the proportion and mixing

　　Water-cement ratio control

　　It is crucial to accurately adjust the water-cement ratio in the concrete mixture. Too high or too low a water-cement ratio will result in poor fluidity or insufficient strength of the concrete, thereby increasing the risk of rebound. Therefore, the construction team needs to regularly check and adjust the injection amount of the accelerator to ensure the stability of the mixture.

　　Monitoring slump

　　Before spraying, the slump (fluidity index) of concrete should be between 140 and 180 mm. This range can better balance the fluidity of the material and the density after molding, which helps to reduce the occurrence of rebound.

　　3. construction operation skills

　　Distance and angle control

　　During spraying, the optimal distance and angle between the nozzle and the sprayed surface are the key factors affecting the rebound rate. It is generally recommended to keep an appropriate distance between the nozzle and the working surface, and the spraying direction is as perpendicular to the sprayed surface as possible (about 90°), so as to obtain the maximum compaction effect and the lowest rebound loss.

　　Circular movement strategy

　　Use continuous and slow horizontal circular movement to spray, each circle covers half of the area of ??the previous circle, forming a "one circle presses half a circle" mode. This uniform distribution method can effectively reduce gaps and enhance structural stability.

　　When encountering a situation where a steel frame or steel mesh is covered, moderately adjust the spray angle to no less than 70°, which can avoid obstacles and maintain a good spraying effect.

　　4. Monitor rebound rate and adjust

　　During construction, the actual rebound rate of concrete should be monitored in real time and construction parameters should be adjusted in time. The target rebound rate is set as: no more than 15% for the side wall and less than 25% for the arch. Once the exceeding standard is found, the cause should be analyzed immediately and corresponding measures should be taken to correct it.

　　The implementation of the above comprehensive measures can not only significantly reduce the rebound loss in concrete wet spraying operations, but also improve the safety, efficiency and final project quality of the entire construction process. This requires construction units to achieve fine management and professional operation in every link from raw material preparation to on-site execution, so as to promote the industry to develop in a more environmentally friendly and economical direction.