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2013FallShotcreteEMag

Technical Tip this difference in velocity distribution. First, the equipped with experimentally validated velocity double-bubble nozzle used in dry-mix shotcrete profiles, the description and optimization of induces more turbulence, slowing down periph- rebound is just around the corner. eral particles, compared with a “convergent” wet-mix nozzle where the air ring seems to references produce the opposite effect. Second, the exis- Armelin, H. S.; Banthia, N.; and Mindess, S., 1999, “Ki- tence of a lubricating layer formed within the nematics of Dry-Mix Shotcrete,” ACI Materials Journal, delivery hose during pumping can also facilitate V. 96, No. 3, May-June, pp. 283-290.Bolduc, L.-S, 2009, “Étude des propriétés de transport du peripheral particle acceleration by reducing fric- béton projeté,” M.Sc. thesis, Université Laval, Québec City, tion with the internal nozzle walls (Kaplan et al. QC, Canada. 2005). Indeed, according to yet-unpublished Jolin, M., and Ginouse, N., 2012, “Recent Research in work conducted in Laval University’s lab on Wet-Mix Shotcrete at Laval University,” Proceeding of the wet-mix shotcrete, the periphery of the wet-mix tures, São Paulo, Brazil, Mar. 20-22. pp -3rd Brazilian Congress on Tunnels and Underground Struc spray contains more cement paste and fine aggre- Kaplan, D.; Larrard, F. D.; and Sedran, T., 2005, “Design gates compared to its core. Therefore, this lubri- of Concrete Pumping Circuit,” ACI Materials Journal, V. 102, cating layer appears to be conserved while No. 2, Mar.-Apr., pp.110-117. passing through the nozzle, confirming its poten- tial effect on peripheral particle acceleration. The average velocities calculated from the centerline and edge velocities provide further Nicolas Ginouse received his information on the effect of equipment and pro- degree in mechanical and cess on outlet velocity. In both cases, average industrial engineering from Art velocities are very similar (61.5 mph 27.5 m/s et Métiers Paritech, Paris, for dry-mix and 64.9 mph 29 m/s for wet-mix). France, in 2010, and he is cur- In our experiments, we used the same input air- rently a PhD Candidate in civil flow of 200 ft3/min (5.7 m3/min) for both pro- engineering at Laval Univer- cesses. Although it is commonly believed that sity, Québec City, QC, Canada. wet-mix shotcrete requires less pneumatic energy His research is supervised by Professor Marc to accelerate the particles than the dry-mix pro- Jolin and deals with the understanding of the cess, in which airflow is also used to convey dry shotcrete placement process controlling rebound material from the gunning machine to the nozzle, and in-place material properties. He is also a the same input airflow generated similar average recipient of the 2010 ASA and ACI Québec-East velocities. To explain this somewhat unexpected Ontario graduate scholarships. Since 2012, he similarity, we must also consider the amount of has pursued his thesis work at King Packaged material (mass) that is accelerated or conveyed in Materials Company, where he leads research and each process. In fact, even if the dry-mix shotcrete development projects on shotcrete and cementi- configuration required more airflow to reach a tious materials as part of the Industrial Innovation given average outlet velocity, our wet-mix shot- Scholarships (IIS) program. crete case required acceleration of about three times more material (in term of mass). The output Dr. Marc Jolin, FACI, is a Full mass rate (pumping rate) was about 6.2 lb/s Professor in the Department of (2.8 kg/s) with the Powercreter 10 against 2.0 lb/s Civil and Water Engineering at (0.9 kg/s) with the Aliva 246.5. Laval University. He received Based on the results presented, it is the nozzle his PhD from the University of type, the shotcrete process, and the output rate of British Columbia, Vancouver, material that will primarily affect the outlet BC, Canada, in 1999. An active velocity distribution. Moreover, in the wet-mix member of Centre de recherche process, the lubricating layer induced by the sur les infrastructures en béton (CRIB), he is cur- pumping phase and the air ring positioning seem rently involved in projects on service life, reinforce- to provide favorable conditions to create a more ment encasement quality, new admixtures, and uniform velocity distribution out of the nozzle. rheology of fresh shotcrete. Jolin is an ASA member; The next phase of this research will take advan- an ACI Examiner for Shotcrete Nozzleman Certifica- tage of the complete velocity profiles generated tion (wet- and dry-mix processes); Chair of ACI and concentrate on the material rebound phase of Committee C660, Shotcrete Nozzleman Certification; the application process. It is believed that, once and Secretary of ACI Committee 506, Shotcreting. 24 Shotcrete • Fall 2013


2013FallShotcreteEMag
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