Why do cement and toothpaste harden?

  Some of you may already know why cement with water hardens over time. Cement is mainly composed of compounds such as calcium silicate and aluminate. When the cement encounters water, these small cement particles will combine with water molecules and then expand, and the gaps between the particles will also decrease accordingly. Over time, the excess water between the particles evaporates, and the particles get closer and closer together, and finally connect together, and the cement hardens accordingly.

Eric Furst, an American professor who studies why pasty materials harden

  Scientists have recently discovered, however, that there are deeper and more general reasons why cement hardens, and that the same principles apply to substances such as toothpaste, paint and clay.
The principle of tight connection between particles

  Researchers from the United States and France collaborated in experiments and found that materials such as cement, toothpaste and silica increase in hardness due to the contact and “linking” of their respective particles to each other, so that The microstructure of the substance is stable. But why are these particles linked together?
  The researchers found that particle contact control occurs because those particles carry ions. Ion-carrying particles are either positively or negatively charged, and these charged particles are then attracted to each other and linked together, forming a stable microstructure, based on the principle that “oppositely charged particles attract each other.”
  We now know what makes substances like cement and toothpaste harden. It’s just that this principle seems a bit simple, so why do scientists spend so much effort to explore it? What is the use of the principle behind the hardening of substances such as cement and toothpaste?
Apply this principle to solve practical problems

  Scientists can use this principle of close connection between particles to predict the properties of material substances. For materials such as cement, we want to know how hard they have hardened; for substances such as paint and toothpaste, we want to know how long before they completely harden (paint becomes hard and peels off, toothpaste becomes Hard will be difficult to use). However, for various reasons, we cannot make accurate predictions about these situations. Therefore, scientists intend to use this principle to build a model to help people better predict changes in material substances.
  In addition, scientists can also add certain chemical substances to the material substance according to this principle to prevent the material substance from hardening and improve performance. In fact, people are already doing it unconsciously. For example, manufacturers add humectants to toothpaste. Molecules in humectants prevent toothpaste particles from touching each other, thereby preventing toothpaste from hardening. But scientists intend to apply this principle to a wider range of materials such as toothpaste, inks and paints, to improve their overall performance and make things made of these materials last longer.