The role of cellulose ethers in controlling shrinkage and cracking of cement mortars

1. Basic characteristics of cellulose ethers

Cellulose Ether is a water-soluble polymer obtained by chemical modification of natural cellulose. It is commonly used in industries such as building materials, coatings and pharmaceuticals. In cement mortar, commonly used cellulose ethers include methylcellulose (MC), hydroxypropylmethylcellulose (HPMC) and hydroxyethylcellulose (HEC).

These cellulose ethers have good water retention, thickening, cohesion and lubricity. They mainly expand in the mortar by absorbing water and form a three-dimensional network structure, thereby affecting the performance of the mortar.

2. The water retention effect of cellulose ether in mortar

One of the most important functions of cellulose ether in cement mortar is to improve the water retention of mortar. Water retention refers to the ability of mortar to retain moisture, which directly affects the hardening and shrinkage properties of mortar. Cellulose ether uses its efficient water-absorbing expansion ability to form a uniform pore structure inside the mortar and reduce the rapid loss of water. This process can significantly slow down the hydration rate of the cement, thereby reducing the risk of early drying shrinkage cracking.

3. Effect of cellulose ether on mortar shrinkage

The shrinkage of cement mortar is mainly divided into dry shrinkage and plastic shrinkage. Drying shrinkage is the volume reduction caused by water evaporation after the mortar hardens, while plastic shrinkage is the volume change caused by water loss during the initial setting stage of the mortar. Cellulose ethers play an important role in controlling both types of shrinkage.

(1). Dry shrinkage control: Through its excellent water retention properties, cellulose ether maintains a high internal humidity of the mortar during the hardening process, thereby slowing down the volume change caused by dry shrinkage. In addition, the uniform pore structure formed by cellulose ether helps disperse stress and reduce the occurrence of cracks.

(2). Plastic shrinkage control: During the initial setting stage, the mortar is prone to plastic shrinkage cracks due to changes in capillary water pressure and rapid evaporation of water. The water absorption and adhesiveness of cellulose ether can increase the viscosity of the mortar, slow down the rate of water loss, and reduce the possibility of plastic shrinkage and cracking.

4. The mechanism of action of cellulose ethers in mortar cracking

Cellulose ethers control the cracking of cement mortars through the following mechanisms:

(1). Improve workability: Cellulose ether can significantly improve the working performance of mortar, including fluidity and water retention, making the mortar more uniform and stable during the construction process. Uniform construction properties help reduce the internal stress generated during the mortar hardening process and reduce the risk of cracking.

(2). Improve mortar strength: Cellulose ether can increase the bonding strength of mortar and improve the bonding performance between mortar and base material, thereby enhancing the overall strength of mortar and reducing the occurrence of cracks.

(3). Delay the hydration reaction: The water retention of cellulose ether makes the water distribution inside the mortar more uniform, delaying the hydration reaction of cement. This delaying effect can reduce the temperature gradient caused by early hydration heat, thereby reducing cracks caused by temperature changes.

(4). Increase cohesion: The three-dimensional network structure formed by cellulose ether in the mortar can increase the cohesion of the mortar, allowing the mortar to resist external stress during the hardening process and reduce the expansion of cracks.

5. Dosage and selection of cellulose ether

The dosage and type of cellulose ethers have a significant impact on their effectiveness in cement mortars. Generally speaking, the optimal addition amount of cellulose ether depends on the specific mortar formulation and construction requirements. Too little addition may not fully exert its water retention and thickening effects, while too much addition may affect the strength and durability of the mortar. Different types of cellulose ethers (such as HPMC and HEC) also have differences in performance and application, and should be selected according to actual needs.

Cellulose ether in cement mortar effectively controls the dry shrinkage and plastic shrinkage of the mortar through its unique mechanisms of water retention, thickening, bonding and cohesion, reducing the risk of cracking. Reasonable selection and use of cellulose ether can significantly improve the construction performance and durability of mortar, and increase the quality and service life of construction projects. In future research and applications, the effects of cellulose ethers under different environmental conditions should be further explored to provide more theoretical and practical support for the optimization of building materials.