ADVANCED MATERIALS & PROCESSES | JULY/AUGUST 2023 24 Alifecycle analysis is a way to evaluate environmental sustainability. It starts with the natural resources used to produce the materials, the type of project to be realized, marketing, the construction phase and the techniques used, management of the infrastructure, maintenance during service life, repairs, restoration, disposal, demolition, reuse, and recycling. This analysis requires that many boundary conditions be clarified. Each step may contribute to sustainability in a “circular economy” way of thinking[1]. Over the last decades, activities related to environmental protection mainly focused on reducing CO2 production. The growing lack of resources and landfill disposal spaces triggered the use of sustainable materials and reuse/recycling of materials, and other tasks that occur at the end of an infrastructure’s service life. This fact is particularly necessary for concrete and cement, some of the most used building materials worldwide, especially across China, India, USA, Brazil, EU, and other countries. CONCRETE AND ENVIRONMENT Reducing CO2 production requires an effort from many in the construction sector. Using sustainable alternatives to partially replace cement clinker, a solid material made during the manufacture of Portland cement, is an important step. Supplementary cementitious materials[2] such as pozzolana, fly ash, granulated ground blast furnace slags, silica fume[3], risk husk, bagasse, wood[4,5] and municipal solid waste slags (Fig. 1), and ashes partially contribute to environmental benefits. These materials may exhibit interesting hydraulic properties or partially act as filler with beneficial effects of the cementitious blends. Their presence on the market is subjected to technology variations. Moreover, changes in materials and energy production processes may limit the future availability of compounds in some geographic areas. In addition, geology and using locally available rocky aggregates may significantly reduce the environmental impact together with a decrease in transportation distances. On the other hand, all these mineral additions need to be carefully monitored with respect to pollutant content. Heavy metals, organic compounds, aluminum, and dioxins are among the detrimental compounds to be verified prior to use as a building material component. Waste materials such as foundry sands, cement kiln dust, marble or rock powders, glass powder, shredded rubber tires, and plastics may have positive effects on concrete[2]. Recently, carbon capture and other new techniques are under investigation, although they may have consequences on cement costs and social impact in developing countries that need to be carefully evaluated[6]. The recent addition of plant coal within concrete may be seen as a further CO2 sink. Nevertheless, the presence of organic elemental carbon within cementitious mixtures requires a deeper look into possible effects on performance. Furthermore, concrete should not be seen as a multiple trash container; this despite the moderate binding capability of some cement types with respect to detrimental ions[7], heavy metals[8], and pollutants. Additional cementitious binders, such as super sulphated, aluminate, ye’elimite, belite, celite, and magnesium- based cements as well as limestone calcined clay cement (LC3), calcined clays, ordinary Portland cement, and calcium carbonate cements[9] indicate an interesting alternative and feasible way to make sustainable concretes. Although classes such as reactive CONCRETE SUSTAINABILITY: A FUTURE PERSPECTIVE As a material widely used around the world, the reuse, recycling, and environmental implications of concrete are important to consider. Christian Paglia* University of Applied Sciences of Southern Switzerland Fig. 1 – Municipal solid waste slag, diameter 1-15 mm. *Member of ASM International
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