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2013FallShotcreteEMag

the Use of recycled Glass in Shotcrete By Isabelle Fily-Paré and Dr. Marc Jolin rmandated to work on the development of mentary cementing materials (SCMs) are now-byproducts, such as slag, fly ash, and silica fume.Once costly material to dispose of, these suppleight after the G8 summit in Japan 2008,the International Energy Agency was technology roadmaps meant to identify specific regularly included in concrete mixture designs. industries and help governments in their quest Their effects on concrete and shotcrete properties, for sustainable development. The concrete—or both in fresh and hardened states, are considered more precisely, the cement—industry was very positive. Consequently, many cement pro- identified as an area with high improvement ducers around the world are now offering pre- potential. Indeed, cement production is respon- blended binary or even ternary cements. sible for about 5% of the total CO emitted in Naturally, the question is whether or not there the atmosphere around the globe.1 The reduc- are other materials that can be used as cement2 tion of those emissions is not a simple chal- replacement. A plentiful supply of recycled glass, lenge; the cement production process involves an environmental issue by itself, has attracted the both high melting temperatures (2500°F attention of researchers2-6 around the world. Pub- 1400°C) and the decarbonation of the raw lished results are very promising, including material (such as limestone), each of which is compressive strength improvement, enhanced responsible for about half of the greenhouse durability of certain types of mixtures, and even gas production. The end result is that for each a water-reducing effect in some cases. ton of cement produced, almost a ton of CO is also generated. recycled Glass2 This leaves us with two simple approaches The recycling of glass is not as simple as it for reducing the carbon footprint of concrete sounds. It is quite unpopular because of the high construction: either modify the cement produc- costs of transportation and the need to sort the tion process (a task cement producers are different colors. It is unfortunately often cheaper actively working on) or, more simply for the for cities to send glass waste to landfills instead end-user, reduce the amount of cement in con- of paying recycling companies to reinsert it in the crete mixtures. consumption loop. As an example, in North America, only 33% of the glass used for glass Food for thought containers is recycled.7 Even when glass is col- Fortunately, brilliant initiatives for partial lected by a traditional recycling truck, only 40% cement replacement have found success in recent of the collected glass is recycled.8 Overall, years. It is interesting to see how concrete became roughly 13% of glass is truly recycled and the a solution for the disposal of many industrial other 87% goes to landfills, even though it would be suitable for a second life. While it may not seem cost-effective to recycle glass, wasting it represents a real problem. In China, for example, the government is considering legislation to make glass recycling mandatory because “glass accounts for 3% of all waste in the cities, and only 5% of it is recycled.”9 The same worries are heard across Europe10 and Asia. the Use of recycled Glass in concrete Fig. 1: Centre for Sustainable Development, The first trials with recycled glass used it as an Montreal (www.maisondeveloppementdurable. aggregate replacement. This approach was highly org/batiment/choix-ecologique-materiaux) appreciated by architects because of the special 14 Shotcrete • Fall 2013


2013FallShotcreteEMag
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