Improving shotcrete: modelling and rebound reduction

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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, the construction of underground spaces and the accelerating of mining undertakings 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 without the need for formwork. Although the technique is used all around the world and has been found to be highly efficient, rapid and economical, concerns are still present with regards to rebound (material losses during placement) and some aspect of its durability.****Using a more fundamental approach than ever before, the projects proposed will benefit from the unique results of a recently completed project. The main objective is to continue and expand the “spray-scale” approach and identify the material and equipment parameters that affect placement and promote the best in-place concrete and overall application. This will allow true development and optimization for reduced rebound and improved durability of shotcrete, providing a reliable construction and repair method. ***The scientific approach is elaborated to meet three specific objectives:****- Understand and describe the effect of the placement techniques on the internal structure (compaction voids & encapsulation of obstacles) of concrete and the associated rebound losses. ***- Pursue the modeling effort to understand and optimize the behavior of fresh shotcrete as it goes through and exits the nozzle, and during impact.***- Offer a unique training experience to a large number of students. ***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; this will lead to both improvements of existing mixture design (reduction of rebound, increased early strength) as well as new and innovative mixture design. It was recently found, for example, that the addition of powdered recycled glass as a SCM has a significant effect on the placement behaviour (high apparent plasticity); the approach proposed here will help understand this effect and exploit it to further reduce rebound and improve quality.***The training of highly qualified personnel is, throughout the project, an important goal by itself. The research program to be proposed will provide a unique training opportunity for a number of graduate students, research assistants and research engineers in the field of concrete materials. The wide variety of issues to be treated, from material behavior characterization to modeling analysis, will promote the development of widely diversified skills. ********