Effect of HPMC on the properties of wet mix mortar

Hydroxypropyl methylcellulose (HPMC) is a polymer compound widely used in building materials, especially in the formulation of wet mortar. It has good water retention, thickening properties, improved construction performance and other characteristics, and can effectively improve the overall performance of mortar.

1. Improve water retention
HPMC has strong water absorption and water retention capabilities, which can significantly improve the water retention of wet-mix mortar. During the construction process, rapid loss of moisture can cause the mortar to shrink and crack, reduce its strength and weaken its bond with the substrate. After adding an appropriate amount of HPMC, a dense molecular network can be formed in the mortar to lock in moisture and prevent it from evaporating too quickly, thus extending the opening time and operability time of the mortar. In addition, high water retention ensures that the cement is fully hydrated, thereby improving the later strength of the mortar.

2. Improve workability
The workability of wet mortar is an important indicator of construction performance, including its fluidity, lubricity and operability. Due to its thickening effect, HPMC can significantly improve the fluidity and adhesion of mortar, making it easier to apply the mortar and evenly cover the surface of the substrate. At the same time, it can also reduce the delamination and bleeding of mortar and ensure good uniformity of mortar during the construction process. This improvement effect can not only reduce the difficulty of construction, but also improve the adhesion between the mortar and the base material and improve the construction quality.

3. Enhance sag resistance
In vertical construction, mortar is prone to sagging, which affects the application effect and construction efficiency. The thickening effect of HPMC can increase the yield stress of the mortar, making it more resistant to sagging in the vertical direction. Especially when applying a thicker mortar layer, HPMC can maintain the shape stability of the mortar and reduce the risk of the mortar sliding down after construction. In addition, the thixotropy of HPMC allows the mortar to maintain a high viscosity in a static state and exhibit good fluidity when subjected to external forces, further improving the construction performance.

4. Improve mechanical properties
Although HPMC is mainly added as a modifier with a low dosage, it still has a certain impact on the mechanical properties of the mortar. An appropriate amount of HPMC can help improve the crack resistance of mortar because its water retention effect can reduce the formation of dry shrinkage cracks. In addition, due to its improvement in the internal microstructure of the mortar, the tensile strength and flexural strength of the mortar are also improved. However, it should be noted that too high a dosage of HPMC may lead to a decrease in the strength of the mortar, as it will increase the air content of the mortar and weaken the compactness of the mortar. Therefore, the addition amount should be strictly controlled when using HPMC, usually 0.1%-0.3% of the cement weight.

5. Influencing factors and optimization
The influence of HPMC on the properties of wet-mix mortar is closely related to its molecular weight, degree of substitution and addition amount. High molecular weight HPMC has a stronger thickening effect, but may have a negative impact on construction performance; low molecular weight HPMC is more soluble and suitable for rapid construction needs. In addition, HPMC with different degrees of substitution also has different performance in water retention and adhesion. In practical applications, the appropriate type of HPMC should be selected based on the mortar formula and construction conditions, and its dosage should be optimized through experiments to achieve a balance between performance and cost.

As an important admixture in wet-mix mortar, HPMC provides support for the overall improvement of mortar performance by increasing water retention, improving workability, enhancing sag resistance and optimizing mechanical properties. Reasonable selection and use of HPMC can not only improve the construction efficiency and durability of mortar, but also reduce construction defects and reduce project maintenance costs. Therefore, in-depth study of the action mechanism of HPMC on the performance of wet-mix mortar is of great significance to modern construction projects.