Hydroxyethyl Methyl Cellulose (HEMC) is a cement mortar admixture commonly used in construction projects. It is a water-soluble polymer compound obtained by chemical modification of natural plant cellulose. The application of HEMC in cement mortar is mainly to improve the workability and construction performance of mortar by improving the rheological properties of mortar (such as fluidity, viscosity, water retention, etc.).

1. Improve the fluidity of cement mortar
As a thickener, HEMC can significantly improve the fluidity of mortar after being added to cement mortar. Its mechanism of action is mainly to increase the flow resistance of cement slurry by forming intermolecular interactions with water molecules and other components in the cement matrix, thereby improving the fluidity of mortar. When the fluidity of mortar is good, it is not only easy to apply and level during construction, but also can avoid stratification or sedimentation of cement mortar, and improve construction efficiency and quality.

2. Improve the viscosity of mortar
HEMC has strong water solubility. After adding HEMC to cement mortar, the viscosity of mortar will be improved. The increased viscosity helps to improve the construction performance of mortar, especially when constructing on vertical surfaces, to prevent mortar from flowing down or falling off. In addition, the viscosity-increasing effect of HEMC also plays a positive role in improving the stability of mortar in high or low temperature environments, especially in extending its operability time.

3. Enhance the water retention of cement mortar
HEMC can effectively improve the water retention of cement mortar, which is an important feature of its common application in the construction industry. Water retention is an important property of cement mortar that keeps water from evaporating or being absorbed during construction. HEMC forms a protective film to prevent rapid evaporation of water and keep the mortar moist, thereby delaying the hydration reaction of cement, avoiding premature drying, and increasing the working time of cement mortar to ensure construction quality.

4. Change the rheological curve characteristics
After HEMC is added to cement mortar, the rheological curve shows the characteristics of non-Newtonian fluid, that is, the viscosity of the mortar changes with the change of shear rate. The shear viscosity of the mortar is high, but when the shear rate increases, the mortar shows shear thinning phenomenon. HEMC can effectively adjust this characteristic, so that the mortar has a higher viscosity at a low shear rate, ensuring the stability during construction; while at a higher shear rate, the fluidity of the mortar is improved, reducing the mechanical burden during construction.

5. Improve the operability and stability of the mortar
The role of HEMC in cement mortar is also reflected in enhancing the stability and operability of the mortar. HEMC, as a stabilizer, can effectively control the hydration rate of the mortar and prevent its stratification, sedimentation and segregation. By adjusting the amount of HEMC added, the ideal mortar operability and stability can be achieved according to different engineering requirements, especially when constructing in high temperature and dry environment, the effect of HEMC is more obvious.

6. Relationship between the amount of HEMC and performance
The amount of HEMC is one of the key factors affecting the rheological properties of cement mortar. Generally speaking, the more HEMC is added, the more obvious its effect of improving rheological properties is, but there are also certain limits. Excessive addition of HEMC may cause excessive viscosity increase of mortar, which will affect the smoothness of construction. Therefore, in practical applications, it is necessary to accurately adjust the amount of HEMC according to the use environment and construction requirements of the mortar.

7. The effect of HEMC on cement mortar after hardening
During the hardening process of cement mortar, the role of HEMC still exists. Although HEMC does not directly participate in the hydration reaction of cement, it can indirectly affect the physical properties after hardening by improving the water retention of cement mortar. For example, HEMC can delay the process of cement hydration, thereby promoting the compressive strength and durability of cement mortar. Mortar treated with an appropriate amount of HEMC usually has better compressive strength and anti-permeability, and is especially suitable for construction projects that require a longer operating time.

As an important additive for cement mortar, hydroxyethyl methylcellulose (HEMC) plays an important role in improving the rheological properties, water retention, viscosity and construction stability of mortar. HEMC can improve the fluidity of mortar, improve workability, enhance the stability of cement mortar, avoid stratification and sedimentation, and thus improve the construction quality of mortar. However, the amount of HEMC needs to be precisely controlled to ensure that the mortar achieves the best rheological properties during the working process and avoid the adverse effects caused by excessive addition. Therefore, in practical applications, the amount of HEMC added should be reasonably adjusted according to different construction conditions and requirements to give full play to its role.