New technologies are making it possible for researchers in MIT’s Concrete Sustainability Hub to make steady progress toward solving this mystery. First they determined that cement paste is a granular material, where the particles or basic nanoscale units pack together most densely when arranged orderly. A few years later they discovered that the calcium-silicate-hydrate (C-S-H) molecules that make up the basic nanoscale unit of cement have a disorderly geometric arrangement, rather than the orderly crystalline structure scientists had long assumed.
In new work, researchers found that the size of C-S-H particles themselves is also somewhat disorderly: The particles form at random sizes, not in homogenous spheres, and this diversity in the size of the nanoscale units leads to a denser, disorderly packing of the particles, which corresponds to stronger cement paste.
The researchers hope this understanding will allow materials scientists and concrete engineers to alter the C-S-H particles at the molecular level to develop stronger, more durable concrete that will have a reduced environmental footprint. If concrete is stronger, less of it is needed. And if it’s more durable, structures made from it will last longer.
Physical Review Letters recently published a paper about this work by Enrico Masoero, postdoctoral associate in the Department of Civil and Environmental Engineering (CEE); Professor Emanuela Del Gado of the Swiss Federal Institute of Technology; Roland J.-M. Pellenq, CEE senior research scientist; Franz-Josef Ulm, the George Macomber Professor in CEE; and Professor Emeritus Sidney Yip of the Department of Nuclear Science and Engineering and the Department of Materials Science and Engineering.
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