HEMC on Cement Hydration

Hydroxyethyl Methyl Cellulose (HEMC) is a nonionic cellulose ether widely used in building materials, especially as a thickener, water retainer and stabilizer in dry-mixed mortar and cement-based materials.

HEMC has excellent water retention properties. In cement-based materials, cement hydration requires a continuous supply of water. HEMC can form a three-dimensional network structure in the cement system through its own high water absorption and film-forming properties, locking free water, thereby improving the water retention capacity of the mixture. This feature is particularly important in dry environments, helping to prevent early water loss and cracking, and improving construction adaptability and later strength development.

HEMC has a delayed effect on the hydration process of cement. Its mechanism mainly includes the following points: First, HEMC swells in water to form a viscous colloidal solution, which covers the surface of cement particles and forms a barrier to prevent water from further diffusing into the cement and delay the hydration reaction; second, HEMC molecules physically adsorb or complex with calcium ions (Ca²⁺) in cement, reducing the activity of these ions and thus slowing down the generation rate of hydration products. Studies have shown that the higher the HEMC dosage, the lower the cement hydration heat release rate and the longer the peak delay time, showing a significant retarding effect.

In terms of microstructure, the addition of HEMC affects the morphology and distribution of cement hydration products. Due to the reduction in hydration rate, the hydration of some cement particles is incomplete, making the hydration product generation process slower and more uniform, which is conducive to the formation of a dense microstructure. At the same time, the polymer network structure formed by HEMC can be used as a skeleton to fill in the cement paste, which helps to improve the integrity of the overall structure. However, if the HEMC dosage is too high, it may cause too many unhydrated cement particles in the cement-based material, thereby affecting the final strength.

HEMC also has a positive effect on the fluidity and construction performance of cement-based materials. The lubricating effect of HEMC improves the plasticity and workability of the slurry, making the material smoother during mixing, smearing and laying. At the same time, high water retention can effectively reduce water seepage and improve bonding performance and surface quality.

In terms of mechanical properties, HEMC has a certain inhibitory effect on the development of early strength, especially in the first 3 days, due to delayed hydration, the strength growth rate is slow. However, as the hydration reaction gradually proceeds, the cement particles in the system are fully hydrated, the microstructure tends to be dense, and the later strength can be restored or even improved. The appropriate amount of HEMC can optimize the construction performance while ensuring the later strength, and is an important means of preparing high-performance dry-mixed mortar.

HEMC in cement-based materials mainly affects the cement hydration process by improving water retention, delaying the hydration rate, and optimizing the microstructure. While its addition improves the workability and durability, it also needs to reasonably control the dosage to avoid adverse effects on early strength. Therefore, in practical applications, the type and dosage of HEMC should be scientifically selected in combination with specific engineering requirements to achieve optimal performance.