To further understand concrete’s microscopic structure and behavior, researchers from the Massachusetts Institute of Technology, Georgetown University, France’s CNRS and peer institutions on both sides of the Atlantic have focused on the principal binder: Is calcium silicate hydrate a continuous solid, like metal or stone, or an aggregate of small particles? Their finding that solidified CSH is a “bit of both” could inform new approaches to lowering mix designs’ water volume and finished structures’ permeability.