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Set Retarder is an additive that reduces the hydration rate and heat of cement or gypsum, extending the setting time.
They are environmentally friendly and biodegradable. Additionally, these retarders can effectively regulate the setting time of materials, making construction more convenient and improving work efficiency. Amino acid retarders can enhance the workability of building materials, making the construction process easier to operate and level. By delaying the setting time, they reduce the risk of cracks during the hardening process, thereby improving project quality. They typically do not negatively impact the final strength and other properties of the materials.
The compositions of gypsum retarders vary widely and mainly include the following categories:
Such as citric acid, sodium citrate, tartaric acid, potassium tartrate, acrylic acid, and sodium acrylate. These retarders can achieve a strong retarding effect with a small amount and are commonly used.
Such as sodium hexametaphosphate and sodium polyphosphate. These retarders work by delaying the setting of gypsum through different chemical reaction mechanisms.
These include certain specific proteins or composites of proteins with other inorganic substances, which also have a significant effect in delaying the setting of gypsum.
Such as calcium sulfate and calcium chloride. These retarders slow down the setting speed of gypsum by reacting with sulfate ions in gypsum, forming insoluble precipitates.
Such as sodium hexadecylbenzene sulfonate and polyethylene glycol, which can regulate the surface tension of gypsum particles, thereby slowing down the crystallization process.
| Product Name | Gypsum Retarder | Batch Number | |||||
| Production Date | Testing Date | ||||||
| Testing Results | |||||||
| No. | Test Item | Quality Indicator | Test Result | Remarks | |||
| 1 | Appearance | White Powder | White Powder | ||||
| 2 | Moisture Content % (105℃) | ＜5.0 | 3.3 | ||||
| 3 | pH (1% Aqueous Solution) | 7.5-8.5 | 7.9 | ||||
| 4 | Bulk Density (Kg/m³) | 600-800 | 706.9 | ||||
| 5 | Fineness@（50 Mesh Residue） | ＜3.0 | 1.1 | ||||
The working mechanisms of different gypsum retarders vary based on their composition:
These mainly work by adsorbing onto the surface of gypsum particles, forming a thin, insoluble film that hinders the hydration reaction of the particles, thus extending the setting time.
These retarders may work by altering the pH value of the gypsum slurry or reacting chemically with other components to delay the setting.
The retarding mechanism may involve interactions between proteins and gypsum particles, as well as the impact of the chemical properties of the protein itself on the setting of gypsum.
These work by reacting with ions in gypsum to form precipitates, which occupy the active surface of the gypsum particles, thereby delaying the setting process.
In summary, different gypsum retarders vary significantly in terms of composition, working mechanisms, performance characteristics, and application areas. The choice of a gypsum retarder should be made by considering the specific application scenario and requirements.
Their production costs are high, resulting in higher prices compared to other types of retarders. Precise control of the dosage is required during use, as improper amounts may affect the final performance of the materials. The applicability of these retarders is limited and may not be suitable for all types of building materials; specific effects need to be tested and adjusted for different materials. Additionally, their storage and stability may be affected by environmental factors, requiring special attention to storage conditions.
