Mechanism of action of HPS in cement mortar

Introduction to HPS

Hydroxypropyl Starch Ether (HPS) is a chemically modified natural starch derivative with good water solubility, stability and rheological adjustment ability. It is widely used in modern dry-mixed mortar systems, especially in plaster mortar, bonding mortar, self-leveling mortar and thermal insulation mortar. HPS can significantly improve the construction performance and use performance of cement mortar with its unique molecular structure, and is an economical and efficient organic polymer additive.

Main mechanism of action of HPS in mortar

2.1. Improve water retention performance

HPS molecular chain contains a large number of hydrophilic hydroxypropyl and hydroxyl functional groups, which can adsorb and lock part of the free water in the mortar system, reducing the rapid loss of mixing water to the porous base or air. This water retention effect helps to extend the open time of the mortar, fully hydrate the cement, increase the strength and reduce the risk of shrinkage and cracking. Especially when constructing a base with a high water absorption rate, the water retention capacity of HPS is particularly important.

2.2. Enhance construction and workability

HPS adjusts the rheological properties of mortar, improves the thixotropy and lubricity of mortar, and makes mortar easier to apply, compact and level. After adding HPS, the "knife stickiness" and "slurry hanging properties" of mortar are improved, reducing the flow and stratification of mortar during construction, which is conducive to obtaining a uniform coating. In addition, the thickening effect of HPS can also reduce the bleeding of mortar to a certain extent and maintain the stability of the construction interface.

2.3. Improve anti-sagging performance

In facade or ceiling construction, mortar often sags due to gravity. HPS improves the yield stress and thixotropy of the mortar system, making it easy to flow when sheared (such as during scraping construction), but quickly restores the viscoelastic structure in a static state, thereby effectively preventing sagging. This mechanism makes HPS an indispensable additive in facade plastering and tile bonding mortar.

2.4. Synergistic effect of water retaining agent to improve comprehensive performance

In dry-mixed mortar system, HPS is often used in conjunction with cellulose ether (such as HPMC). The molecular structure of HPS is more flexible than that of cellulose ether, and its water absorption and release rate is faster. It can quickly provide water retention effect in the early stage of construction, complementing HPMC and improving the overall stability and working performance of mortar. This synergistic effect can also optimize material costs and reduce the amount of cellulose ether.

2.5. Improve the crack resistance and surface quality of mortar

Good water retention and uniform hydration reaction reduce the shrinkage cracks of mortar. In addition, HPS makes the water distribution of mortar more uniform during the hardening process, reduces porosity, and improves interfacial bonding, thereby improving the surface flatness and crack resistance of mortar.

Microscopic analysis of the action principle

HPS mainly forms hydrogen bonds with water molecules in mortar through the spatial network structure of molecular chains, changing the rheological behavior of the system. Since HPS is a non-ionic polymer, its adsorption effect on cement particles is weak and will not significantly affect the hydration reaction of cement. However, by changing the microstructure and water distribution of the slurry, it improves the construction window and stability of the mortar. In addition, HPS can also reduce the free water migration rate of the mortar system, thereby delaying water seepage and improving the initial strength.

Application effect and economy

Practice shows that adding 0.1%~0.3% HPS to ordinary cement-based mortar can significantly improve the construction performance, reduce sagging and water seepage, and improve the coating quality. Its dosage is low and cost-effective, and it is suitable for promotion and application in various types of dry-mixed mortars. For construction personnel, HPS can bring a smoother operating feel and longer adjustment time, improve construction efficiency and finished product quality.

The mechanism of action of HPS in cement mortar is mainly reflected in water retention and thickening, improving construction performance, improving anti-sagging performance, and synergizing with other additives to improve the comprehensive performance of mortar. By adding HPS reasonably, the mortar can achieve better working performance and surface quality while reducing material costs. It is an important functional additive in modern building dry-mix mortar systems.