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2015SpringShotcreteEMag

ASA Graduate Student Scholarship 2014-2015 Research Updates TStudent Scholarship recipients. The 2014-15 scholarships and impact energy on the substrate2,3; to gather this particulardata requires quite the laboratory setup given the number ofvarying parameters in a shotcreting session (air, water andhe following are three short updates on graduate studentresearch being undertaken by ASA’s 2014-15 Graduate were announced at the February 2015 ASA Annual Meeting, material flows, movement of the nozzle, distance, mixture Awards Banquet, and in the Winter 2015 issue of Shotcrete. design, and so on). • Simon Bérubé is currently pursuing his MSc in civil engi- In the continuation of Ginouse’s recent works4 on the char- neering from Laval University, Quebec City, QC, Canada. acterization of the shotcrete spray, this research project, con- • Pasquale Basso Trujillo is a PhD Candidate at Laval Uni- ducted under the supervision of Marc Jolin at Laval University, versity. will be focusing on the placement process of shotcrete and the • Qian Wu is a graduate student majoring in civil engineering phenomena that takes place during a spraying session. The at the University of Texas at Austin, Austin, TX. main objective of this research is to further the understanding We hope they find the research into shotcrete­related topics of conditions that facilitate a good inclusion of shotcrete par- rewarding, and we look forward to getting future updates on ticles, such as reduced rebound. the research results. The first part of the experimental program tested a certain number of nozzles and recorded images of the spray produced by each of them. To achieve this, a high-speed imaging system provided numerous images for the calculation of particle Simon Bérubé received his BEng in civil velocities at up to 1250 images per second. engineering from Laval University in 2014 The second objective of the project was to characterize the and is currently pursuing his MSc in civil parameters that combine sufficient velocity and kinetic energy engineering from the same university. His to a particle at the moment it impacts onto the fresh shotcrete research project at Laval is centered on the substrate in a way to ensure it is captured and does not kinematics of the shotcrete spray. The study rebound. To understand what conditions are favorable to the aims to provide a better understanding of incorporation of incident particles into the substrate, the next the rebound phenomenon and to express the step of the experimental program measured the spatial distri- impacting materials’ energy within the spray. Bérubé plans to bution of the particle’s masses on the receiving surface to pursue a career in concrete and/or shotcrete projects, as his obtain the mass distribution of the accumulation of shotcrete main field of interest is centered on cementitious materials. materials produced by a fixed­point nozzle. Ultimately, we will connect velocities and masses to express the energy Research: Study of the Placement Process profiles of the particles at different distances from the nozzle. and Rebound of Shotcrete By knowing which particles adhere to the fresh substrate among various sections of the spray, it will be possible to Introduction and Background establish which part of the spray is efficient and which part Despite the constant evolution of new shotcrete equipment of it produces rebound. This will turn into a unique charac- solutions and the recent progress in our understanding of the terization tool to evaluate a given nozzle’s efficiency at placement process,1 a significant factor remains in the shot- reducing rebound. crete industry: losses of materials by rebound. Even under the best conditions and by following the rules of good prac- Significance of Research Project tice, losses will often account for 10% of the material; this Material losses from rebound represent significant financial amount can climb to 30% of the total quantity of materials losses in the shotcrete industry and represent as much as 30% used in adverse and difficult conditions. In this regard, it is of the total amount of materials used. By furthering the under- safe to say that rebound losses have a significant financial standing of shotcrete rebound, it would be possible to lower impact on the use of shotcrete. This situation is not at all easy the operational costs for the shotcrete sector of the construction to deal with, because to have a chance at solving the problem industry. Following Ginouse’s initial work,1 this project of rebound, it requires an excellent comprehension of the describes the kinematics of shotcrete particles and their incor- placement process and the mechanisms behind it, access to poration among the substrate within the spray for the first time. shotcreting equipment, and a well-equipped laboratory. This understanding hopes to contribute solutions to lowering Indeed, the velocities and spatial distribution of the incident the loss of larger aggregates, which tend to rebound the most shotcrete particles are key parameters to understand rebound among all incident particles, thus affecting the mechanical 54 Shotcrete • Spring 2015


2015SpringShotcreteEMag
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