The content of redispersible polymer powder
November 25th 2024
Consistency and Workability: When redispersible latex powder is incorporated into mortar, it disperses upon mixing with water. This process allows the polymer to enhance the consistency of the mortar, which initially increases and then decreases with further addition of the latex powder. This occurs because the polymer particles, being large and viscous, increase the cohesion of the mortar, reducing its flowability and increasing its consistency. Despite this, the stratification (separation of layers) remains relatively unchanged, maintaining the mortar’s workability and suitability for construction.
Strength Properties: The addition of redispersible latex powder generally leads to an improvement in flexural strength and bond strength of the mortar. However, compressive strength tends to decrease as the polymer content increases. This decrease is attributed to the lower elastic modulus of the polymer compared to that of cement paste and aggregates, which weakens the mortar under compression. Additionally, with the increase in tensile strength, the mortar tends to fail in shear under compression, as the polymer forms a weak interlayer with low shear strength.
Impermeability: The inclusion of redispersible latex powder significantly enhances the waterproofing properties of the mortar. This improvement is due to two main factors:
Physical Filling and Film Formation: The polymer particles fill larger and connected pores within the hardened mortar, reducing the number of pathways for water penetration. The formation of a continuous polymer film further seals these pores, improving the mortar’s impermeability.
Chemical Interactions: The organic components of the polymer interact with the inorganic materials in the mortar, forming a dense waterproof bonding layer that effectively prevents water ingress.
Early Strength Development: The initial increase in flexural strength at 7 days is slower with lower polymer content. This can be explained by the reduced number and connectivity of pores in the paste after polymer addition. The presence of polymer restricts water penetration into the mortar, delaying the hydration process and affecting the early development of strength.
Air Induction and Flexibility: Redispersible latex powder induces air in the mortar, providing hydrophobic properties, breathability, and compressibility. This improves the mortar’s application properties and makes it easier to work with. Additionally, the inclusion of flexible polymers enhances the deformability of the rigid cement matrix, resulting in a significant increase in both flexural and bond strengths.
Microstructure Enhancement: As the mortar hydrates and dries, the redispersible latex powder particles coalesce to form a continuous film within the pore structure. This film integrates with the cement hydration products, creating a dense network that significantly improves the mortar’s structural integrity and waterproofing performance.
In summary, redispersible latex powder enhances the performance of waterproof mortar by improving its consistency, workability, flexural strength, bond strength, and impermeability. It achieves this through physical filling and film formation, chemical interactions, and by enhancing the mortar’s microstructure. However, it may reduce compressive strength due to the lower elastic modulus of the polymer compared to traditional cementitious materials.
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