Influence of air pressure on the rheological behaviour of shotcrete fibre-reinforced cementitious composites for structural strengthening

In the realm of structural strengthening and protection, the shift toward automation is essential to boost productivity and address the labour shortage. Robots facilitate precise and efficient shotcrete application, however, quality control remains challenging, as robotic methods provide less flexibility than manual techniques. Careful selection of parameters is vital to maintain quality and consistency in applying sprayed layers without formwork. Previous research has demonstrated the viability of using shotcrete to apply a strengthening layer of strain-hardening cementitious composites (SHCC). However, compressed air mixing with the material alters its rheological properties after spraying, unlike those of freshly mixed material before spraying. This study focuses on the influence of air pressure on material parameters including density, air void content, and static yield stress. The impact of air pressure on static yield stress is measured in the fresh state using fast penetration tests. These tests are conducted on fresh material both before and after spraying to assess how pumping and spraying affect its properties. By deepening our understanding of the mixture’s rheological behaviour throughout the shotcrete process, this research aims to improve SHCC printing efficiency and reduce the risk of application failure.