Faculty Profile: Franz-Josef Ulm

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Professor, Department of Civil and Environmental Engineering

Franz-Josef Ulm joined the MIT faculty in 1999, after serving as head of the Composite Concrete Materials Division at the Laboratoire des Ponts et Chaussees in Paris. Ulm is a world leader in research on cement-based materials. He has made important innovations in both theory and experiment, including developing experimental tests to provide basic information on the smallest scale and extending mathematical techniques to predict the behavior of concrete on the macro-scale. In previous experiments on concrete weathering, his lab showed the likely long-term deterioration of concrete containments designed to isolate radioactive wastes.

What’s the environmental impact of concrete?
Ulm: Concrete is the second most widely consumed material in the world, after water. One ton of cement, the primary component of concrete, produces about one ton of CO2 in its manufacture and use, which is roughly the equivalent of what a tree can absorb in 100 years. Worldwide production of cement stands now between 2 and 3 billion tons per year. This creates between 5 and 10 percent of all atmospheric CO2. My students did a study that shows that increasing the strength of concrete by a factor of x reduces the environmental impact by a factor of 1/x. If concrete were to be produced with the same amount of initial material to be seven times normal strength, we could reduce the environmental impact by 1/7. Maybe we can use nanoengineering to create such a green high-performance concrete.

What information do you get from nanoengineering studies?
Ulm: First you have to realize that everything we see at a larger scale is the result of how matter organizes at a smaller scale: electron scale, atom scale, clusters of microstructure, which then cluster again to become what we see as building materials, which we put together into structures. Everything at those smaller scales is what makes a larger structure behave the way it behaves.

For instance, in my lab we took samples of the glue that holds concrete together—cement paste—from different mix designs, different locations and different cement plants, and tested them at a very small scale in the lab. Each time, we found the same two fundamental properties: the stiffness and strength were always the same, independent of the type and source of the material. We were astonished, because everyone is accustomed to thinking—from macroscopic testing—that material from one manufacturing plant varies from the next.

It turns out that there is a fundamental way that these materials organize at the nano-scale. The fundamental building block of concrete—calcium silica hydrate (c-s-h) particles—organizes around two limit packing densities: 64 percent (like randomly packed oranges in a box) and 74 percent (like stacked oranges). This, it turns out, corresponds to the mathematically proved limit packing densities allowed by Nature for spherical objects. If cement always packs at these densities, this indicates that its strength might come not only from the c-s-h particles, but from their packing density. What would happen if we changed the basic materials or altered the packing density at the micro-scale? This work began in 2000 with an idea from Giorgios Constantinides, a former student who is now a professor in Cyprus. At the time, I didn’t believe that going to the micro-scale would provide information valid for engineers. More recently, Matthieu Vandamme, who earned the Ph.D. last year and is now a researcher at Ecole de Ponts, found that you could get ultra-high-density c-s-h if you add smaller objects to fill the space between particles.

How nano is nano?
Ulm: Nano-scale is 10-9 meters. Atomic level is roughly one order of magnitude smaller than that. The aim of our lab is to make a link between atomic structure and the properties at the nano-scale and bring this information up to the macro-scale.

Is that feasible?
Ulm: Some people in the industry have already created ultra-high-performance concrete, which reaches steel-like strengths. Bridges made from this material are much lighter and their construction doesn’t interrupt traffic, because they can be pre-cast and installed in one night. But these newly engineered materials generally have been used as boutique materials for aesthetic projects. The FHWA did install one test bridge in Iowa in 2006, and it performed perfectly.

Until recently, the big question was, “Where’s the money to implement this?” I hope the new administration, if it generates an infrastructure renewal program, will put efforts into sustainable development. If we use these sorts of new materials to revive our infrastructure, we can have a big environmental impact, elevate the social status of our workers through increased training to use these new materials, and create economic growth. These three components—economic growth, social development and environmental protection—are the definition of sustainable development as set forth in the Rio Declaration on Environment.