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Sustainability (a) (b) Fig. 5: Substitution of 20% by volume of natural aggregates by: (a) plastic; and (b) rubber aggregates could also have some potential in ground support, where a higher deformability and energy absorption is sometimes sought. Even though the rubber aggregates did not have any influence on the rebound behavior, they have shown unexpected behaviors in fresh shotcrete. The texture of this shotcrete was nothing like any other one tested before; the consistency of the fresh shotcrete was very soft, but the cohesion was very high at the same time. Also, the mixture generated almost no dust in the shooting even at low water content (pre-bagged material, hydromix nozzle). This result is likely due to improved mixing in the nozzle created by the rubber particles bouncing against the hose or some electrostatic action of the fine rubber particles. This interesting behavior is quite new in dry-mix shotcrete and could have great potential in confined spaces such as tunnels and mines, where the reduction of dust is valuable. It is clear that more research is needed. Future Our studies have shown that nontraditional ingredients produced from waste materials can lead to new and very promising behaviors in drymix shotcrete, albeit the wettest consistency may not be best practice anymore. The use of all these new sustainable materials challenge the way we have used shotcrete for many years and may help us aim for an ever-improving design of concrete mixtures for shotcrete placement (Fig. 7). Now that we have some examples of waste products that can be recycled in shotcrete as cement or aggregate replacement, we have to consider unconventional approaches to their use. There are virtually limitless possibilities for us to design new shotcrete mixtures in the pursuit of more sustainable development. Reinventing shotcrete mixtures could still be sufficient in many applications considering the large replacement rate used and the possible optimization of the mixtures (Fig. 6). Because of their low stiffness, plastic and rubber Fig. 6: Strength behavior of dry-mix shotcrete containing rubber and plastic aggregates as sand replacement STRUCTURAL SHOTCRETE SYSTEMS, INC. LICENSE #579272 A www.structuralshotcrete.com JASON E. WEINSTEIN, P.E. VICE PRESIDENT 12645 CLARK STREET (562) 941-9916 SANTA FE SPRINGS, CA 90670 FAX (562) 941-8098 30 Shotcrete • Fall 2016


2016FallShotcreteEMag
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