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2016SpringShotcreteEMag

ASA Graduate Student Scholarship 2015-2016 Research Update The following is a short update on the graduate student research being undertaken by ASA’s 2015-16 Graduate Student Scholarship recipient. The 2015-16 scholarship winner was announced at the February 2016 ASA Annual Meeting, Awards Banquet, and in the Winter 2016 issue of Shotcrete. Antoine Gagnon is currently pursuing his MSc in civil engineering from Laval University, Quebec City, QC, Canada. We hope he finds the research into shotcrete-related topics rewarding and we look forward to getting future updates on the research results. Antoine Gagnon received his bachelor’s degree in civil engineering from Laval University, where he continues to work toward his master’s degree in the same field. The focus of his graduate research is in developing shotcrete mixture designs with added environmental/sustainable value. Toward that end, Gagnon is exploring the reduction of waste associated with shotcrete rebound and inclusion of industrial waste and recycled materials to minimize the use of new resources, all with an eye toward conventional and environmental costs as well as sustainable performance. Research: Developing Shotcrete Mixture Designs with Environmental Added Value Background For decades, the concrete industry has been working on reducing its environmental footprint by optimizing working techniques, using high-performance materials, and increasing the use of alternative materials. In the shotcrete industry, this avenue also appears to be very promising, but unfortunately very few studies have been conducted regarding this subject and significant changes have yet to come. As we know, multiple recycled products and industrial waste can be used in concrete as replacement for cement or aggregates. However, the control of the workability of the fresh concrete is often the limiting factor with such mixtures. The key to this problem is the shotcrete dry-mix process method. Indeed, this method allows the unhydrated material to easily flow with air right until it is wetted down at the nozzle, only a short moment before it reaches the spraying surface. This process opens the door for the use of multiple materials that would normally decrease the workability of cast-in-place concrete. On the other hand, waste produced by rebound of the shotcrete causes a great deal of concern. Rebound represents wasted resources that generates direct material costs, disposal and cleaning costs, along with environmental externalities. Generally averaging from 10 to 40%, depending on various parameters, rebound is a problem in terms of economy, physical properties of concrete, and environmental footprint. Enhancing shotcrete efficiency by lowering the rebound would therefore address these compatible issues. Objectives In this research, the first objective is to reduce waste associated with shotcrete rebound by developing highefficiency shotcrete mixture designs. These shotcrete mixture designs will contain supplementary cementitious materials such as modified clays and gums designed to have lower rebound. All shotcretes will be characterized both in the fresh and hardened states to better evaluate their potential. The second objective is to minimize the need for new resources. Thus, other mixtures with substitute materials will be evaluated. These alternative ingredients are industrial waste and recycled materials such as paper sludge ashes, recycled concrete, or recycled plastic. Finally, the third objective is to measure the potential of these mixtures in terms of conventional costs, environmental costs, and sustainable performance. If the results are promising, this research could contribute to legitimize shotcrete with environmental added value in the industry. Research Significance Ironically, most waste materials will keep generating costs and energy consumption as they are normally sent to landfills or treated. Alternatively, they could be used as substitute materials in shotcrete and save new resources. This situation could become a win-win strategy as the concrete producer, the waste producer, and the environment could all benefit from this collaboration. Shotcrete mixture designs have a great potential in terms of energy efficiency and sustainable development—both permanent issues of our technological challenges. It is all about managing our resources in a better way. In a world of limited resources, adapting the shotcrete industry to sustainable development standards is essential to guarantee its prosperity. If the results of this research show potential for new shotcrete mixture designs with environmental added value, it would help enhance the environmental footprint in the shotcrete industry. As the carbon market is now a part of our economy, becoming a leader in sustainable development is one of the best ways to grow in a thriving industry. 12 Shotcrete • Spring 2016


2016SpringShotcreteEMag
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