Hydroxypropyl methylcellulose (HPMC) is a widely used additive in mortar compositions and has a variety of functions that improve the performance and workability of the mortar. Content includes the chemical structure of HPMC, its interaction mechanisms in the mortar matrix, and its impact on the properties of fresh and hardened mortars.

Mortar is an essential ingredient in construction that acts as a binder for masonry units, providing cohesion and stability to the structure. The performance of the mortar significantly affects the integrity and longevity of the building, so additives are required to adjust its properties. Among these additives, hydroxypropyl methylcellulose (HPMC) emerges as a versatile ingredient that provides a wide range of benefits to mortar compositions. This article elucidates the role of HPMC in mortar formulations, elucidates its impact on various properties, and explores the underlying mechanisms controlling its functionality.

1.Chemical structure and properties of HPMC
Hydroxypropyl methylcellulose belongs to the cellulose ether family and is derived from cellulose through chemical modification. Substitution of hydroxypropyl and methyl groups on the cellulose backbone gives HPMC unique properties, including water solubility, film-forming ability, and surface activity. The degree of substitution (DS) and molecular weight (MW) significantly affect the performance of HPMC in mortar compositions, with higher DS improving water retention and lower MW improving dispersion.

2. Mechanism of action
HPMC affects mortar properties through various mechanisms, mainly due to its interaction with water and cementitious materials. After hydration, HPMC molecules form a protective colloid around the cement particles, retarding water evaporation and promoting hydration. This enhances the water retention of the mortar matrix, extending workability and reducing the risk of cracking. In addition, HPMC can also be used as an adhesive to improve the adhesion between the mortar and the base material, thereby enhancing the bonding strength and reducing shrinkage.

3. Effect on the performance of fresh mortar
In fresh mortars, HPMC offers several desirable properties, including improved consistency, adhesion and ease of application. By modifying the rheological behavior of the mortar, HPMC improves workability and pumpability, allowing for efficient placement and compaction. In addition, HPMC reduces the tendency to segregation and bleeding, ensuring uniformity and homogeneity of the mortar mixture.

4. Effect on the performance of hardened mortar
In hardened mortars, the presence of HPMC helps enhance durability, strength and resistance to environmental factors. By optimizing water distribution and cement hydration, HPMC promotes the development of a dense microstructure, reduces permeability and improves mechanical properties. In addition, HPMC minimizes shrinkage and cracking during drying and curing, thereby improving dimensional stability and reducing maintenance requirements.

5. Practical considerations for using HPMC
Optimizing the performance of HPMC in mortar compositions requires careful consideration of various factors, including dosage, particle size, and compatibility with other additives. Excessive dosage of HPMC may lead to prolonged setting time and early strength reduction, so it needs to be chosen wisely according to specific requirements. Particle size distribution also affects the dispersion and effectiveness of HPMC in mortars, with finer particles exhibiting superior water retention properties. In addition, compatibility testing with other admixtures is crucial to avoid adverse interactions and ensure synergistic effects.

Hydroxypropyl methylcellulose (HPMC) is a valuable additive in mortar compositions and offers several advantages in improving performance and workability. With its ability to enhance water retention, adhesion and durability, HPMC plays a key role in optimizing the performance of both fresh and hardened mortars. By understanding the underlying mechanisms of HPMC function and considering preventive measures through practical considerations of its use, researchers and practitioners can fully exploit its potential to advance mortar technology and meet the ever-changing needs of the construction industry.