The main components of building gypsum and high-strength gypsum are β-type hemihydrate gypsum and α-type hemihydrate gypsum, which are mixed with water; semi-water gypsum will be rehydrated to form dihydrate gypsum, which will release heat and solidify into a certain strength. Hardened body.
The hemihydrate gypsum is first dissolved after adding water, and then hydrated to form dihydrate gypsum; since the solubility of dihydrate gypsum is lower than that of hemihydrate gypsum, dihydrate gypsum is precipitated from the supersaturated solution by colloidal particles. Due to the precipitation of dihydrate gypsum, the balance of the dissolution of hemihydrate gypsum is destroyed, and the hemihydrate gypsum continues to dissolve and hydrate. The dissolution of the hemihydrate gypsum and the precipitation of the dihydrate gypsum are continuously performed until the hemihydrate gypsum is completely consumed. In the above process, the free moisture in the gypsum slurry is gradually reduced by hydration and evaporation, and the slurry is gradually thickened. And lose plasticity, a process called condensation. Thereafter. The slurry continues to thicken, and the dihydrate gypsum gradually aggregates into crystals, which gradually grow, symbiosis and staggered to form a crystalline structure network. In this process, the slurry gradually hardens and the strength continues to increase, forming a hardened body with a certain strength, and the strength stops growing until it is completely dry. This process is called hardening.
The theoretical water demand meter for the hydration reaction of hemihydrate gypsum is 18.6% of its weight, in order to make the slurry have sufficient fluidity. The usual amount of water added is much larger than the theoretical water requirement: therefore, the hardened gypsum slurry contains a large amount of pores. The β-type hemihydrate gypsum in the building gypsum is mostly flaky, cracked crystal with fine grain and large specific surface area. When the gypsum slurry is mixed, the water requirement is 60%-80%, so the porosity after hardening is large. , the intensity is low. And in high-strength plaster. The type of hemihydrate gypsum has good crystallinity, coarse crystal grains and small specific surface area. When it is prepared into a plastic slurry, the water requirement is about 35% to 45%, and the porosity after hardening is small, so that it has high strength.
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