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2014FallShotcreteEMag

Shotcrete Corner it is out of sync with the concrete pump you will to the wet-mix nozzle or the air can keep the get varying degrees of hard and soft shotcrete accelerator from getting into the air stream. Con- mixture on the sprayed surface. trol the accelerator dosage with the pump. The Use a positive displacement pump such as a pump should have a variable speed drive; and use peristaltic or rotor-stator pump (Fig. 2 and 3). that to control the flow. These pumps should all Make sure that the pump pressure is 10 to 15 psi have stainless steel fittings due to the corrosivity (0.07 to 0.10 MPa) higher than the air pressure of alkali-free accelerators. There are all sorts of wet-mix nozzles on the market and everyone has their preference. Some nozzles have a connection for the accelerator on one side of the nozzle and the air connection on the other side. Some have only one inlet to the nozzle that is split into two. The type of nozzle shown tends to mix the accelerator into the concrete better than the ones with separate inlets. Better yet is to pump the accelerator into the air stream a few feet back from the nozzle, don’t use a regulating valve for the accelerator. Simply an on-off valve allows for control of the accelerator with the pump (Fig. 4). Dan Millette, a Mining Engi- neer, is the Director of the Mining and Tunneling Division Fig. 2: Peristaltic accelerator pump of The Euclid Chemical Com- pany. Millette has over 30 years of experience in the shotcrete industry and is a certified EFNARC Nozzleman Examiner. He is a member of ACI Subcommittee 506-F, Shotcreting-Underground, as well as a member of the Society for Mining, Metallurgy and Explo- ration (SME); the Canadian Institute for Mining, Metallurgy and Petroleum; and the Tunneling Association of Canada. Fig. 3: Rotor-stator accelerator pump Marc Jolin, FACI, is a Full Professor in the Department of Civil and Water Engineering at Laval University. He received Air inlet his PhD from the University of British Columbia, Vancouver, BC, Canada, in 1999. An active member of Centre de Recherche Accelerator inlet sur les Infrastructures en Béton (CRIB), he is currently involved in projects on service life, reinforcement encasement quality, new admix- tures, and rheology of fresh shotcrete. Jolin is an ASA member; an ACI Examiner for Shotcrete Nozzleman Certification (wet- and dry-mix pro- cesses); Chair of ACI Committee C660, Shotcrete Nozzleman Certification; and Chair of ACI Com- Fig. 4: Acme nozzle with accelerator port mittee 506, Shotcreting. 46 Shotcrete • Fall 2014


2014FallShotcreteEMag
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