What is bentonite?
A: Bentonite, also known as montmorillonoid, is the layered aluminosilicate with montmorillonite as the main component. The cationic species between layers of bentonite determine the type of bentonite. If the interlayer cation is Na +, it is called sodium bentonite; if Ca+, it is called calcium bentonite; if H+, it is called hydrogen bentonite (activated clay); if organic cation, it is called organic bentonite.
Generally the materials with a particle size of 1-100nm are called to nanomaterials. The particle size of bentonite is nanoscale. It was naturally formed millions of years ago, so bentonite is called the natural nanomaterial abroad.
Bentonite has a very strong hygroscopic property, can absorb the amount of water equivalent to 8-20 times that of its volume and swell to 30 times. In an aqueous medium, it can be dispersed into a colloidal suspension, and has a certain viscosity, thixotropy, and lubricity. The mixture of it with sediment has plasticity and adhesion, as well as stronger cation exchange capacity and adsorption capacity. Bentonite is known as “universal clay,” and widely used in metallurgy, petroleum, foundry, food, chemical engineering, environmental protection and other industrial sectors.
What is bentonite?What’s the action mechanism of bentonite in the mortar?
A: Bentonite is a swellable material, which will absorb a large amount of water during the swelling process so as to reduce the free water in the mortar, resulting in the decrease in the fluidity of mortar and acceleration of fluidity loss. Bentonite is a silicate similar to montmorillonite and mainly has the columnar structure, so after its hydrolysis, in the mortar it can increase the stability of mortar. Meanwhile, its unique sliding effect, to a certain extent, can improve the sliding properties of the mortar and increase the pumpability.
In the pure water medium, montmorillonite can show all the above properties, while in the water containing salt, all the above properties then will change a lot. After the hydration of cement in the mortar, it will form the silicate and sulfate solution, which is rich in calcium and sodium ions, greatly weakening the swelling, viscosity, thickening, lubricity and thixotropic properties of montmorillonite. And montmorillonite plays a hindering role in the cement hydration, macroscopically manifested as the decrease of strength and increase of shrinkage. Therefore, montmorillonite must be modified so that it can still maintain the swelling, viscosity, thickening, lubricity and thixotropic properties even in the medium of salt solution rich in calcium and sodium ions.
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