Cement Americas

SPR 2013

Cement Americas provides comprehensive coverage of the North and South American cement markets from raw material extraction to delivery and tranportation to end user.

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CEMENTSCOPE arrangements possible for homogenous-sized spheres with the highest density occurring when particles arranged in an orderly pattern. However, Ulm's nanoindentation experiments (poking a tiny dot of cement paste with an even smaller needle and measuring the resistance), which relate the hardness of a nanoscale unit to its packing density, indicate that C-S-H particle strength occurs on a spectrum, suggesting that there could be more than two packing densities. In the new models, parameters for particle size were opened up to range from 3.5 to 35 nanometers. These models' predictions of C-S-H particle packing densities agree with the spectrum shown by the earlier nanoindentation tests. PARTICLE INTERACTION A second important insight comes from the model's assumption that particles interact. When they touch, they stick together, and when they stick together, the cement is stronger. When they touch, they stick together, and when they stick together, the cement is stronger. the interactions between particles at the meso scale. The meso scale, Masoero said, has been "like this valley of death in between" the nano and macro scales that was difficult to study because some key quantities for the interactions could not be computed from the molecular structure of the particles, before Pellenq's work. The next step will be to learn how to improve the sticking of the particles and their packing densities by playing with the chemistry of the raw materials. "We feel our work supports an emerging awareness that funda- "Before we thought of C-S-H particles as grains with no sticking together," said Enrico Masoero, a department postdoctoral associate. "Now we assume there are interactions between the particles and the strength of the interaction determines the strength of the material." They extrapolated from Pellenq's work at the nanoscale that the interactions between molecules within a particle would determine "The challenges involved in the molecular-level understanding of cement hydration are related to problems in the aging and degradation of materials, which are related to environmental sustainability. With the new awareness of this connection, progress in one problem could be effectively translated into insights in another." Particle packing density research was funded by MIT Concrete Sustainability Hub, Swiss National Science Foundation and Schlumberger. Denise Brehm is Senior Communications Officer of Massachusetts Institute of Technology Department of Civil and Environmental Engineering. PHOTO: MIT Department of Civil and Environmental Engineering The researchers know this from the atomic-scale modeling work of the Hub's Roland Pellenq, the Civil & Environmental Engineering senior research scientist who determined the basic structure of a C-S-H particle and the behavior of molecules within the particle. mental advances in cement research have the potential to transform an entire industry that is critical to global welfare," said MIT Department of Materials Science and Engineering Professor Emeritus Sidney Yip. (from left) Enrico Masoero, Franz-Josef Ulm and Roland Pellenq use fruit as a visual metaphor for the packing density of diversely sized cement nanoparticles. www.cementamericas.com • Spring 2013 • CEMENT AMERICAS 5

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