Shotcrete placement automation for improved quality and zero rebound losses

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The need for construction methods that are rapid, efficient, economical and, above all, durable is more important than ever as it is the key to durable design and service life optimization. Infrastructures repair and rehabilitation of all kinds, the construction of underground spaces and the mining undertaking in challenging grounds have increased sharply over the last decades; they all have in common the extensive use of shotcrete. Shotcrete is regularly used to place concrete on vertical and overhead surfaces with obvious advantages: excellent compaction and adhesion, the absence of complex formwork and the possibility to encapsulate reinforcement. The possibilities in both mixture designs and types of applications are almost limitless. Examples such as the extensive use of massive structural shotcrete walls and shoring elements in recent constructions in the Toronto area are witnesses of the ever-advancing nature of shotcrete. However, despite having been invented more than a 100 years ago and its increasing usage around the world, the final quality of placement -amount of rebound losses, correct consolidation and proper reinforcing bars encapsulation- is yet still in the hands of the nozzleman. The long-term objective of this research proposal therefore is to improve our understanding of the mechanisms that control the placement of shotcrete in order to improve the placement quality and the technological process, to design new equipment, and to optimize the mixture design methods. This objective is further built upon through the exploration of automated placement techniques for producing high quality structural shotcrete, using a fully programmable 6-axis industrial robot recently acquired in the laboratory. We indeed find ourselves at an interesting and never attained before moment in shotcrete research and development: on the one hand, we have a better understanding than ever of the fundamental mechanisms of shotcrete placement dynamics involving substrate rheology and material velocity (and hence rebound reduction, adequate consolidation and complete reinforcement encapsulation) while, on the other hand, we are discovering how the automation of placement allows for precise control of the nozzle movements and trajectories, which opens the way to further reduce rebound losses and improve placement quality by exploiting, adapting, and controlling shotcrete rheology as well as precise nozzle movement during placement. The novelty and uniqueness of the approach is the coupling of full-scale production of shotcrete in a controlled environment and the optimization brought by study of the spray and particle impact on the surface. The proposed research program is designed to leverage the unique facilities and the know-how developed at Université Laval over the years with its fully equipped for indoor, year-round shotcreting in a controlled environment and offering life-size equipment for both dry-mix and wet-mix shotcrete.