Effects of HPMC on the Performance of Wet-mix Mortar

Wet-mixed mortar is a mixture of cement, fine aggregate, mineral admixtures, admixtures, additives, and water in a particular proportion. After being measured and mixed in a mixing station, the mortar will be transported to the place of use and used within a specified time. The raw materials used in wet-mixed mortar do not need to be dried, and there is no need to set up storage tanks, mixers, and other equipment on site. So it has the advantages of low cost, centralized mixing, stable quality, and green manufacturing.

Under the current construction situation where manual operations are still the mainstay, the supply of wet-mixed mortar at one time must be larger than the one-time construction. It determines that wet-mixed mortar must be used for a long time and still has good water retention and consistency. Thus, the two technical indicators of wet-mix mortar mixture’s water retention rate and setting time have become the key to its popularization and application.

1. HPMC can improve the water retention and cohesion of the wet mortar mixture, But excessive addition will reduce the consistency of the wet mortar mixture

As we know, HPMC is used as one of the main additives of mortar due to its excellent water retention performance. It can enhance the consistency of wet-mixed, reduce the bleeding rate of mortar to a certain extent, and improve the fluidity of wet-mixed mortar within a specific dosage range. Yet, too high content of HPMC makes the wet-mix mortar too cohesive. It will reduce the fluidity of the mortar and makes the mortar more challenging to construct.

2. HPMC will increase the tensile bonding strength of wet-mixed mortar

HPMC will reduce the compressive strength of wet-mixed mortar, and the reduction is more significant. But it can be used to increase the tensile bonding strength of wet-mixed mortar. On the one hand, the cellulose ether and the hydration particles form a thin layer of a polymer film. It can produce a sealing effect and prevent water loss. So that it has enough moisture to ensure the hydration and strength development of the cement and improve the bonding strength of the paste. On the other hand, HPMC enhances the cohesiveness of the wet-mixed mortar to ensure its good plasticity and flexibility. It reduces the slip stress between the wet-mixed mortar and the substrate specimen interface and further improves the interface bonding ability of the mortar.

3. It is recommended that during the preparation process, HPMC is mixed into the wet-mixed mortar in the form of a solution rather than directly integrated with the form of a powder

The former has a better effect on improving water retention, cohesion, and mechanical properties of wet-mixed mortar. When the converted content of HPMC is in the range of 0.01%~0.04%, the water retention rate of HPMC in solution form is 1.4%~3.0% higher than that of powdered HPMC in wet-mixed mortar. Thus, HPMC mixed in the form of a solution has a better effect on improving the water retention of wet-mixed mortar.