China is rich in bentonite resources and reserves. Because of its excellent performance, it has been widely used in many fields. In building waterproof engineering, it is used to manufacture waterproof materials with different properties. In recent years, its popularization and application has shown a strong momentum of development and achieved good social and economic benefits. This has broad prospects for the promotion and application of bentonite.

   Bentonite is usually a clay rock, mainly composed of montmorillonite. Montmorillonite is a kind of aqueous aluminosilicate containing a small amount of alkaline soil metal, belonging to monoclinic crystal system. The crystal is a 2:1 layer of silicate, consisting of two layers of silica and four layers of hydrogen and eight layers of oxygen. The number of ions in the octahedron is 2. The number of cations in the tetrahedron is 4. When the low valence cations in octahedron (ladder tetrahedron) replace the high valence cations in the same way, the original structure will increase the equivalent negative charge. The interlayer compensation of water-absorbing or anhydrous cations and polar molecules leads to the expansion and dispersion of fine particles in the direction perpendicular to the layer, and has the ability of adsorption and cation exchange. According to these characteristics, various waterproof materials are manufactured.

   Bentonite has strong water absorption and will hydrate in case of water. It can be expanded to 10~20 times the original volume. The reasons are as follows: (1) Bentonite has a large specific surface area and can absorb a large amount of water. (2) The crystal structure of bentonite allows water molecules to enter the lattice layer and expand. (3) The surface of each particle is negatively charged and repels each other. Bentonite has good water retention after hydration. Even under high pressure, water will not be discharged to form thick gel. Its impermeability is very low. After natural drying for 10cm/s, bentonite still has the ability to absorb water and expand after absorbing water, and can expand repeatedly.