Innovations in cement-based materials: Addressing sustainability in structural and infrastructure applications
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Introduction Global per capita consumption of concrete has increased since 1970 from less than 1 tonne per person per year to nearly 2.5 tonnes per person per year today. By 2030, it is projected to increase to more than 3 tonnes per person per year (Figure 1).1,2 At the same time, the world population has increased from 3.7 billion to more than 7 billion people, meaning that 20 Gt of concrete is placed in service each year. To meet infrastructure needs in regions where population growth is highest, cement production has increased steeply, more than doubling in Africa and in the former Soviet Union and more than tripling in Asia during 2001–2014 alone.1 In developed regions with more stable or even decreasing populations, infrastructure maintenance, including reconstruction to maintain serviceability and moderate expansion to facilitate economic growth, is apparent through more modest increases of 25–50% in cement production during this period. With worldwide production in excess of 4 billion tonnes annually, Europe is the only region where cement production has remained relatively consistent since the turn of the 21st century.2 Because of the vast quantity of cement-based materials produced each year, there is much to be gained through improvements in the manufacturing of cement and the production of concrete in terms of meeting societal demand in an increasingly sustainable manner. Even those who are engaged in sustainable development on a global scale and at the forefront of technological innovation recognize
the important role key advances in commodity materials such as concrete can play in sustainability. For example, Bill Gates supports the idea—originally proposed by Vaclav Smil’s Making the Modern World: Materials and Dematerialization—that concrete is the most important human-made material. Gates cites the economic and health (or sanitation-related) benefits of concrete construction, while also recognizing that technological advances are needed to reduce the environmental impacts of the material’s vast use.3 Although “concrete” and “cement” are used interchangeably colloquially, cement is one component of concrete, along with water and fine and coarse aggregate (i.e., sand and crushed rock or gravel, respectively). The cement and water combine chemically over time to form heterogeneous hydrated phases that bind the mineral aggregates together, forming a waterresistant composite material. In modern concrete production, a portion of the cement might be replaced or augmented with finely divided siliceous or aluminosiliceous minerals (often industrial by-products), called supplementary cementitious materials (SCMs). Chemical admixtures and fibers might also be included in the mix, and reinforcing bars or strands— commonly carbon steel—can also be used as continuous reinforcement in concrete members. With kiln temperatures exceeding 1400°C, modern manufacturing of cement clinker (i.e., the cement components formed within the kiln) is a highly energy-intensive process
Kimberly E. Kurtis, School of Civil and Enviro
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