What Are The Measures To Improve The Waterproof Performance Of Gypsum Products At Home And Abroad?

At present, there are two main measures to improve the waterproof performance of gypsum products at home and abroad: (1) product surface coated with sodium methylsilanol, chlorine partial emulsion waterproofing agent and waterproof finish, the method is simple and easy, if can be strictly operated, can obtain more ideal waterproof effect. However, once coated products surface or local defects, or due to improper waterproof treatment, exposed gypsum will be dissolved in water, resulting in coating, finish peeling, reduce the waterproof effect. In order to ensure the formation of crystallized structure of gypsum hardened slurry, the compactness of the product is improved under the premise of certain strength. To fundamentally improve the internal structure of gypsum products, add a certain amount of Portland cement or active volcanic ash material slag, fly ash, zeolite and activator in gypsum, so that it has a hydraulic calcium silicate hydrate or calcium aluminate hydrate in the process of hydration and hardening, strength and stability and waterproof performance are better than dihydrate gypsum. Although the hydration products produced by this method can improve the wet strength and softening coefficient of the products, the hydration products do not belong to the category of gypsum cementitious materials. In addition, when gypsum is mixed with active mixed materials, gypsum and active mixed materials react with each other, forming waterproof components at the same time, gypsum fast hardening, high early strength characteristics have changed.(2) gypsum is mixed with water emulsion or water soluble hydrophobic material accounting for less than 5% of the total gypsum cementing material, control and adjust the hydration and water absorption rate of gypsum, reduce the water absorption rate of gypsum products, improve its waterproof performance. For example, mixing organic silicon to change the surface energy, mixing paraffin, asphalt, rosin and so on to increase the density, close the gap, and polymer resin to form composite material, the formation of water resistant film, improve the strength, adhesion, wear resistance, so as to improve the moisture-proof, waterproof performance. However, the fracture load of the plate decreases obviously, which can be attributed to the fact that the mixed hydrophobic organic materials isolate the effect of gypsum and water, thus improving the softening coefficient of gypsum, but also reducing the contact point of gypsum crystal, weakening the strength of the crystal structure network. This kind of gypsum to reduce the absolute strength of gypsum and excellent porous structure to improve the gypsum resistance to water, obviously is not ideal, but most of our moisture-proof decorative gypsum board with this technique.Chemical admixtures are used to improve the water resistance, mainly by reducing the solubility of gypsum (improve the softening coefficient), reduce the absorption of gypsum to water (reduce water absorption) and reduce the erosion of gypsum (water isolation) and other ways. The admixtures used to reduce the solubility include: ammonium borate, oxalic acid and its salts, phosphoric acid, phosphate, stearic acid, barium hydroxide and synthetic fatty acids, etc. The purpose is to convert calcium sulfate dihydrate with large solubility into calcium borate and calcium oxalate with small solubility. Change the surface energy: silicone waterproof agent, silicone resin and resin prepolymer. The silicone emulsion changes the surface energy within a certain length by infiltrating the port of each pore, that is, the contact Angle with water is changed, so that the water molecules condense together to form droplets, blocking the infiltration of water, and maintaining the permeability of gypsum. By adding water reducing agent to reduce the water consumption, can reduce the void fraction of gypsum hardened slurry, adding water reducing agent can speed up the early hydration of gypsum, but has no effect on the final hydration rate, its addition can make gypsum crystals well developed, on the one hand to promote the growth of building gypsum crystals, skeleton enlargement, particle thickening, needle crystals greatly reduced, on the other hand, The gypsum crystal is made into a relatively complete columnar compact structure, and small acicular crystals are bonded between the large skeleton of the gypsum hardened body. As the water reducing agent promotes the formation of amorphous hydration gel, it also reduces the pores between crystals, thus improving the mechanical properties of gypsum hardened body and improving its strength. However, after adding water reducing agent, it will bring obvious slump time loss, so other admixtures need to be added to improve the performance.