There are limitations in improving the performance of gypsum paste by single admixture. If the performance of gypsum mortar is to achieve satisfactory results and meet different application requirements, chemical admixtures, admixtures, fillers and a variety of materials are needed to compound and complement each other scientifically and reasonably.
1. The coagulant
Regulating coagulant is mainly divided into retarder and coagulant. In gesso dry mix mortar, the product that uses cooked gesso to make up all uses delay coagulate agent, use anhydrous gesso or the product that uses 2 water gesso to make up directly needs to promote coagulate agent.
2. Retarder
By adding retarder to gypsum dry mixed building materials, the hydration process of semi-hydrous gypsum is inhibited and the solidification time is prolonged. The hydration conditions of gypsum plaster are various, including the phase composition of gypsum plaster, temperature of gypsum material, particle fineness, setting time and pH value of finished product. Each factor has a certain influence on the effect of retarding, so there are great differences in the amount of retarding agent under different circumstances. At present, the better domestic gypsum special retarder is metamorphic protein (high protein) retarder, it has the advantages of low cost, long retarder time, small strength loss, good construction, long opening time and so on. In the bottom type stucco gypsum preparation amount is generally in 0.06% ~ 0.15%.
3. The coagulant
Accelerating the stirring time of slurry and prolonging the stirring speed of slurry are one of the physical methods to promote coagulation. The chemical coagulants commonly used in anhydrous gypsum powder building materials are potassium chloride, potassium silicate, sulfate and other acids. The dosage is generally 0.2% ~ 0.4%.
4. Water retention agent
Gesso dry mix building materials cannot leave protect water agent. To improve the water retention rate of gypsum product slurry is to ensure that water can exist in gypsum slurry for a long time so as to obtain a good hydration and hardening effect. Improving the constructability of gypsum powder building materials, reducing and preventing the segregation and bleeding of gypsum slurry, improving the slurry flow hanging, prolonging the opening time, solving the engineering quality problems such as cracking and empty drum are inseparable from water retaining agent. Whether the water-retaining agent is ideal depends mainly on its dispersibility, quick solubility, molding, thermal stability and thickening, among which water retention is the most important index.
Cellulose ether water-retaining agent
At present, hydroxypropyl methyl cellulose is the most widely used in the market, followed by methyl cellulose, and carboxymethyl cellulose. The comprehensive properties of hydroxypropyl methyl cellulose are better than methyl cellulose. The water retention of hydroxypropyl methyl cellulose is much higher than that of carboxymethyl cellulose, but the thickening effect and bonding effect are worse than that of carboxymethyl cellulose. In gypsum dry mixed building materials, the amount of hydroxypropyl and methyl cellulose is in the range of 0.1% ~ 0.3%, and the amount of carboxymethyl cellulose is in the range of 0.5% ~ 1.0%.
Starch water-retaining agent
Starch kind protects water agent basically uses at gesso be putty in child, face layer model stucco gesso, can replace partial or total cellulose kind protects water agent. The workability, constructability and consistency of slurry can be improved by adding starch water-retaining agent to gypsum dry building materials. Commonly used starch water-retaining agent products are cassava starch, pre gelatinized starch, carboxymethyl starch, carboxypropyl starch. Starch kind protects water agent dosage to be in 0.3% ~ 1% commonly, if dosage is too big meeting makes gesso product produce mildew phenomenon below damp environment, affect project quality directly.
③ Glue type water retaining agent
Some instant adhesives can also play a better role in water retention. Such as 17-88, 24-88 polyvinyl alcohol powder, green gum and guar gum used for bonding gypsum, gypsum putty, gypsum insulation glue and other gypsum dry mixed building materials, in a certain amount of the case, can reduce the amount of cellulose water retention agent. Especially in fast sticking gypsum, it can replace cellulose ethers in some cases.
(4) Inorganic water retaining materials
The application of composite other water-retaining materials in gypsum dry mixed building materials can reduce the amount of other water-retaining materials, reduce the cost of products, and improve the workability and constructability of gypsum slurry. The commonly used inorganic water retaining materials are bentonite, kaolin, diatomite, zeolite powder, perlite powder, attapulgite clay, etc.
5. Adhesive
The application of adhesive in gypsum dry mixed building materials is inferior only to water retaining agent and retarder. Gesso self leveling mortar, adhesive gesso, caulking gesso, heat preservation gesso glue can not leave adhesive agent.
Redispersible latex powder:
Redispersible latex powder is widely used in gypsum self-leveling mortar, gypsum insulation glue, gypsum caulking putty and so on. Especially in gypsum self-leveling mortar, it can make the slurry viscidity, good fluidity, to reduce stratification, avoid bleeding, improve crack resistance and so on also played a great role. Usage is generally 1.2% ~ 2.5%.
Instant polyvinyl alcohol:
At present, the instant dissolved polyvinyl alcohol with more dosage on the market is 24-88, 17-88 the product of two models, often used at adhesive plaster, gesso, gesso compound heat preservation glue, stucco plaster and other products, dosage is in 0.4% ~ 1.2% commonly.
Guar gum, field gelatin, carboxymethyl cellulose, starch ether and so on are adhesives with different bonding functions in gypsum dry mixed building materials.
6. Thickener
Thickening is mainly to improve the workability and fluidity of gypsum slurry, which is similar to adhesive and water retaining agent, but not completely. Some thickening agent product is good in thickening respect effect, but respect is not ideal in cohesive force, water retention rate. When making up gypsum dry powder building materials, the main effect of admixture should be considered fully so as to apply admixture better and more reasonably. Commonly used thickener products are polyacrylamide, green gum, guar gum, carboxymethyl cellulose.
7. Air-entraining agent
Air entraining agent is also known as foaming agent, mainly used in gypsum insulation glue, plaster plaster and other gypsum dry mixed building materials. Air entraining agent (foaming agent) helps to improve construction, crack resistance, frost resistance, reduce bleeding and segregation phenomenon, the dosage is generally in 0.01% ~ 0.02%.
8. Defoaming agent
Defoaming agent is often used at gesso self-leveling mortar, gesso caulking be putty in, can raise the density of material pulp, strength, water resistance, caking sex, dosage is in 0.02% ~ 0.04% commonly.
9. Water reducing agent
Reducing water agent can improve gesso slurry fluidity and gesso hardening body strength, usually at gesso self leveling mortar, stucco gesso. At present, domestic water reducing agent is polycarboxylic acid retarding water reducing agent, melamine high-efficiency water reducing agent, tea system high-efficiency retarding water reducing agent, lignosulfonate water reducing agent according to fluidity and strength effect. In addition to water consumption and strength, it is necessary to pay attention to the setting time and fluidity loss of gypsum building materials when using water reducing agent in gypsum dry mixed building materials.
10. Waterproofing agent
The biggest defect of gypsum products is poor water resistance. The area with larger air humidity has higher water resistance requirements for gypsum dry mixed mortar. Generally, the water resistance of gypsum hardened body is improved by adding hydraulic admixture. Under the condition of wet or saturated water, the softening coefficient of gypsum hardened body can reach 0.7, so as to meet the requirements of product strength. Chemical admixtures can also be used to reduce the solubility of gypsum (that is, increase the softening coefficient), reduce the absorption of gypsum to water (that is, reduce water absorption) and reduce the erosion of gypsum hardened body (that is, water isolation) water resistance pathway. Gypsum waterproof agent has ammonium borate, methyl sodium silicate, silicone resin, milk fossil wax, the effect is better and silicone emulsion waterproof agent.
11. Active activator
Natural and chemical anhydrous gypsum can be activated to make it sticky and strong, so as to be suitable for the production of gypsum dry mixed building materials. Acid activator can accelerate the early hydration rate of anhydrous gypsum, shorten the setting time and improve the early strength of gypsum hardened body. Alkaline activator has little effect on the early hydration rate of anhydrous gypsum, but it can obviously improve the later strength of gypsum hardened body, and can form part of hydraulic cementing material in gypsum hardened body, which effectively improves the water resistance of gypsum hardened body. The application effect of acid-base compound activator is better than that of single acid or basic activator. Acid activators include potassium alum, sodium sulfate, potassium sulfate and so on. Alkaline activators include quicklime, cement, cement clinker, calcined dolomite and so on.
Thixotropic lubricant
Thixovariable lubricant is used in self-leveling gypsum or stuccoing gypsum, which can reduce the flow resistance of gypsum mortar, prolong the opening time, prevent the stratification and settlement of slurry, so as to make slurry get good lubricity and construction, while making the hardened body structure uniform, increase its surface strength.
Post time: May-25-2022