What is the application of RDP in dry-mixed mortar system?

Redispersible polymer powder (RDP) is the core functional additive of modern dry-mixed mortar system. It is a powder material prepared by ethylene-vinyl acetate copolymer (EVA) or vinyl acetate-ethylene copolymer (VAE) emulsion through advanced spray drying technology. This material can be quickly redispersed to form a stable colloid after contacting water. Its physical and chemical properties are highly consistent with the original emulsion. This unique property makes it show excellent application value in the field of building materials.

In the preparation process of dry-mixed mortar, RDP significantly improves the material performance through the following mechanism:

Interface enhancement effect: polymer particles migrate to the mortar-substrate interface area during cement hydration, forming a continuous polymer film with a three-dimensional network structure, which effectively improves the interfacial bonding strength. According to experimental measurements, the bonding strength of the mortar system with 2% RDP added can be increased by 40%-60%.

Cohesion optimization mechanism: The dispersed polymer particles fill the pore structure of cement stone and form an elastic connection network through physical cross-linking, so that the mortar has excellent flexibility and deformation resistance. ASTM C109 test data shows that the elastic modulus of mortar with RDP can be reduced by 30%-50%.

Stress buffering function: The polymer film can effectively absorb and disperse the internal stress caused by temperature changes, humidity fluctuations or loads, and prevent the generation and expansion of microcracks. According to the EN 12004 standard test, the lateral deformation capacity of tile adhesive containing RDP can reach more than 5mm.

Water retention regulation function: The formation of polymer film significantly reduces the capillary osmotic pressure of the mortar system, prolongs the hydration reaction time, and ensures that the cement is fully hydrated. According to the DIN 18555-7 test results, the addition of RDP can increase the water retention rate of mortar to more than 98%.

Key performance improvement indicators include:

Adhesion strength: Improved by 200%-400% (EN 1348)

Flexural strength: Increased by 30%-50% (ISO 679)

Impact resistance: Improved by 3-5 times (ASTM D2794)

Freeze-thaw cycle: Mass loss after 50 cycles <5% (GB/T 50082)

In specific application scenarios, different dosages of RDP show differentiated performance:

Tile adhesive (dosage 1.5%-3.0%): Wet adhesion ≥1.0MPa, slip <0.5mm

External wall insulation mortar (dosage 2.0%-4.0%): Compressive strength/flexural strength ratio ≤3.0

Self-leveling mortar (dosage 0.5%-1.5%): 28d flexural strength ≥8MPa

Repair mortar (dosage 3.0%-5.0 %): Bond strength ≥ 2.0MPa

The current technology development trend focuses on the development of functionalized RDP, including:

Anti-efflorescence type: Reduce Ca(OH)₂ migration through ion complexation technology

Early strength type: Introduce nano-nucleating agent to accelerate polymer film formation

Hydrophobic type: Grafted organic siloxane increases the contact angle to above 115°

The implementation of this technical solution can significantly improve the service performance of buildings and extend the maintenance cycle to 3-5 times that of traditional mortar, which meets the requirements of GB/T 50378 green building evaluation standards. It is recommended to optimize the synergistic ratio of RDP with cellulose ether, water reducer and other components through orthogonal experiments according to specific engineering needs to achieve the best cost-effectiveness.