Is Cement a Glassy Material?

TL;DR

This study investigates the nanoscale structure of calcium-silicate-hydrate (C--S--H) in cement, providing evidence that it is amorphous with intermediate order, mainly due to hydration effects, challenging the crystalline model.

Contribution

The paper offers a detailed simulation-based analysis demonstrating that C--S--H is amorphous with partial crystalline features, clarifying its structural nature.

Findings

C--S--H is amorphous with intermediate order

Its structure retains some crystalline characteristics

Hydration mainly causes the amorphous state

Abstract

The nature of Calcium--Silicate--Hydrate (C--S--H), the binding phase of cement, remains a controversial question. In particular, contrary to the former crystalline model, it was recently proposed that its nanoscale structure was actually amorphous. To elucidate this issue, we analyzed the structure of a realistic simulation of C--S--H, and compared the latter to crystalline tobermorite, a natural analogue to cement, and to an artificial ideal glass. Results clearly support that C--S--H is amorphous. However, its structure shows an intermediate degree of order, retaining some characteristics of the crystal while acquiring an overall glass-like disorder. Thanks to a detailed quantification of order and disorder, we show that its amorphous state mainly arises from its hydration.