Set in stone? A perspective on the concrete sustainability challenge
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Set in stone? A perspective on the concrete sustainability challenge Krystyn Van Vliet, Roland Pellenq, Markus J. Buehler, Jeffrey C. Grossman, Hamlin Jennings, Franz-Josef Ulm, and Sidney Yip As the most abundant engineered material on Earth, concrete is essential to the physical infrastructure of all modern societies. There are no known materials that can replace concrete in terms of cost and availability. There are, however, environmental concerns, including the significant CO2 emissions associated with cement production, which create new incentives for university–industry collaboration to address concrete sustainability. Herein, we examine one aspect of this challenge—the translation of scientific understanding at the microscale into industrial innovation at the macroscale—by seeking improvements in cement-paste processing, performance, and sustainability through control of the mechanisms that govern microstructure development. Specifically, we consider modeling, simulation, and experimental advances in fracture, dissolution, precipitation, and hydration of cement paste precursors, as well as properties of the hardened cement paste within concrete. The aim of such studies is to optimize the chemical reactivity, mechanical performance, and other physical properties of cement paste to enable more sustainable processing routes for this ubiquitous material.
Sustainability challenges and opportunities With more than one-half of the world’s growing population (now ∼7 billion) living in cities, a sustainable physical infrastructure is central to improving and maintaining a high quality of life. Concrete is an important component of this infrastructure, with a current annual per capita consumption of about 2.8 tonnes (t) (Figure 1). Concrete powers a worldwide US$35 billion industry, employing more than two million workers in the United States alone. This high demand is driven by a number of remarkable properties of this material (Table I), with which a structural composite with complex geometry and high strength can be created on demand by mixing water with cement powder and stone. This “liquid stone” processing capacity enables rapid construction and repair of geometrically complex pavements, bridges, buildings, and waterways. However, such high usage carries a price associated with Earth’s finite resources and limited tolerance for industrial byproducts. Sustainable use of concrete requires that its function and costs (in economic, environmental, energy, and social terms) be evaluated within the context of its end use and
that new and highly optimized materials be developed (Table I). Life-cycle assessment shows quantitatively that the greatest environmental burden from structures such as buildings occurs during the use stage,5 which presents new priorities for the exploration of property and processing optimization. As illustrated in Figure 2, concrete is manufactured locally and directly from readily available limestone and clay, which are mixed without refinement and then heated in a large, rotating kiln (up to 200
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