Cellulose ether is a type of organic polymer compound widely used in building materials, especially in cement-based materials. Cellulose ether can delay the hydration process of cement, thereby adjusting the workability, setting time and early strength development of cement paste.
(1). Delayed hydration reaction
Cellulose ether can delay the hydration reaction of cement, which is mainly achieved through the following mechanisms:
1.1 Adsorption and shielding effects
The high viscosity solution formed by dissolving cellulose ether in aqueous solution can form an adsorption film on the surface of cement particles. The formation of this film is mainly due to the physical adsorption of hydroxyl groups in cellulose ether molecules and ions on the surface of cement particles, which results in the surface of cement particles being shielded, reducing the contact between cement particles and water molecules, thereby delaying the hydration reaction.
1.2 Film formation
In the early stages of cement hydration, cellulose ether can form a dense film on the surface of cement particles. The existence of this film effectively hinders the diffusion of water molecules into the interior of the cement particles, thereby delaying the hydration rate of the cement. In addition, the formation of this film can also reduce the dissolution and diffusion of calcium ions, further delaying the formation of hydration products.
1.3 Dissolution and water release
Cellulose ether has strong water absorption, can absorb moisture and release it slowly. This water release process can adjust the fluidity and workability of the cement slurry to a certain extent, and slow down the rate of hydration reaction by reducing the effective concentration of water during the hydration process.
(2). Influence of cement phase composition
Cellulose ethers have different effects on the hydration of different cement phases. Generally, cellulose ether has a more obvious effect on the hydration of tricalcium silicate (C₃S). The presence of cellulose ether will delay the hydration of C₃S and reduce the release rate of early hydration heat of C₃S, thereby delaying the development of early strength. In addition, cellulose ethers can also affect the hydration of other mineral components such as dicalcium silicate (C₂S) and tricalcium aluminate (C₃A), but these effects are relatively small.
(3). Rheology and structural effects
Cellulose ether can increase the viscosity of cement slurry and affect its rheology. High viscosity slurry helps reduce the settling and stratification of cement particles, allowing the cement slurry to maintain good uniformity before setting. This high viscosity characteristic not only delays the hydration process of cement, but also improves the fluidity and construction performance of cement slurry.
(4). Application effects and precautions
Cellulose ethers have a significant effect in retarding cement hydration and are therefore often used to adjust the setting time and fluidity of cement-based materials. However, the dosage and type of cellulose ether need to be precisely controlled, because excessive cellulose ether may cause problems such as insufficient early strength and increased shrinkage of cement-based materials. In addition, different types of cellulose ethers (such as methylcellulose, hydroxypropylmethylcellulose, etc.) have different mechanisms and effects in cement slurries, and need to be selected according to specific application requirements.
The application of cellulose ether in cement-based materials can not only effectively delay the hydration reaction of cement, but also improve the construction performance and durability of the material. Through reasonable selection and use of cellulose ethers, the quality and construction effect of cement-based materials can be significantly improved.
Post time: Aug-03-2024