Ceramics in the Environment

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ceramics in the environment Ancient lessons: Roman concrete durable, green Scientists working to make modern concrete more durable and sustainable are focusing their attention on ancient technology. Specifically, a research team led by Paulo Monteiro of the US Department of Energy’s Lawrence Berkeley National Laboratory and the University of California, Berkeley, has analyzed samples from a 2,000-year-old Roman concrete breakwater to determine why the concrete is so durable, how its manufacture was more environmentally sound, and how to adapt those characteristics to modern concrete production. “It’s not that modern concrete isn’t good. It’s so good we use 19 billion tons of it a year,” Monteiro says in a news release. “The problem is, manufacturing portland cement accounts for seven percent of the carbon dioxide that industry puts into the air.” Portland cement acts as the primary binding agent in modern concrete, but its production is an energy-intensive process. Roman concrete used 10 percent less binder that was produced at a temperature only 2/3 of that needed for processing portland cement, according to the researchers. Team member Marie Jackson, a research engineer of civil and environmental engineering at UC, Berkeley, obtained the sample of Roman concrete used for underwater structures from a breakwater in Pozzuoli Bay near Naples. Roman engineers produced the material by mixing lime and volcanic ash (pozzolan) to form mortar, then packing the mortar and volcanic tuff into wooden forms. Seawater hydrated the lime and reacted with the ash to cement the mixture together. “In the mid-first-century BC, there was an explosive advance of technology in concrete,” Jackson says. “The Romans needed to find a mix that would work for building harbors for shipping and military purposes.” With the help of classics scholars, Jackson went back to the Latin texts describing the concrete technology of the time. Based on translations and characterization observations, she says a special mix was used for seawater exposure applications. “Caesar Augustus must have standardized the mix because we see that all of the concrete samples used a specific ash from a specific eruption.” Fast forward a few centuries and scientists used Berkeley Lab’s Advanced Light Source as well as facilities at UC, Berkeley, the King Abdullah University of Science and Technology in Saudi Arabia, and the BESSY II synchrotron at Germany’s Helmholtz-Zentrum Berlin für Materialien und Energie to discover how Roman concrete differs from the modern material. They found that the binder in modern concrete is a compound of calcium, silicates, and hydrates. The binder phase of Roman concrete contains aluminum and has lower silicon content. X-ray spectroscopy indicated that the aluminum substitution may be responsible for the durability of the seawater concrete: The ancient material contained a rare hydrothermal mineral, aluminum tobermorite, that is absent in modern concrete formulations. The researchers determined tobermorite has higher stiffness than modern concrete binders and may serve as a model for future concrete strength and durability. Full results are reported in the JACerS paper “Material and elastic properties of Al-tobermorite in ancient Roman seawater concrete.”n Cree moves in commercial, retail LED markets Cree Inc., Durham, N.C., recently announced it was “redefining the midpower LED market” with the introduction of a family of ceramic-based LEDs “that offers no-compromise performance and reliability.” According to the company, “… the ceramic-based XH LEDs are designed to deliver the long L70 lifetimes at hightemperature and high-current operation of Cree’s other high-power LEDs, such as XP and XT LEDs. In comparison, plastic LEDs are known for short L70 lifetimes at high-temperature and highcurrent operation. The XH LEDs allow lighting manufacturers to offer products that meet the reliability expectations of LED technology.” Products include easy-to-use retrofit or upgrade kits for linear fluorescent lighting with a claimed typical payback period of only two years. Cree says the kits use 50 percent less energy, provide better light, and last up to twice as long as the standard 32-W fluorescent lamps they replace. The two-year payback period is based on a comparison to a fluorescent three-lamp setup used 12 hours per day with electricity costs of $0.11 per kWh. On the consumer front, Cree recently announced an exclusive marketing deal with Home Depot. The company is retailing 40- and 60-W equivalent bulbs starting at $9.97. n Drill core of concrete from a 2,000-year-old Roman breakwater consists of pumice (yellowish inclusions), lava and other volcanic crystalline materials (dark and gray spots), and lime (white). Inset: scanning electron micrograph of aluminum tobermorite crystals believed to provide the superior durability and mechanical properties of Roman seawater concrete. (Credit: Lawrence Berkeley National Laboratory.) American Ceramic Society Bulletin, Vol. 92, No. 6 | www.ceramics.org 17


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