Size diversity in cement nanoparticles optimizes packing density to give concrete its strength

November 8, 2012

By Denise Brehm
Civil and Environmental Engineering

Concrete may be one of the most familiar building materials on Earth, but its underlying structure remains a bit of a mystery. Materials scientists and concrete engineers still don’t fully understand exactly how the cement paste that works as glue in concrete hardens during the first hours after water and cement powder are mixed.

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.

Particle size implications 

In new work, they found that the size of C-S-H particles themselves is also somewhat disorderly: The particles form at