Effect of Redispersible Latex Powder on the Properties of Cement Mortar

Effect of Redispersible Latex Powder on the Properties of Cement Mortar

Redispersible latex powder exhibits excellent redispersibility: upon contact with water, it re-disperses into an emulsion, with chemical properties virtually identical to those of the original emulsion. When incorporated into cement- or gypsum-based dry-mix mortars, redispersible latex powder can enhance a wide range of mortar performance characteristics, including improved bond strength and cohesion; reduced water absorption and lower elastic modulus; enhanced flexural strength, impact resistance, wear resistance, and durability; and superior workability.

Mechanical properties and water resistance

The incorporation of latex powder into cement mortar forms a highly flexible and elastic polymeric network film, which significantly enhances the mortar’s performance, particularly its tensile strength. Under external loading, the increased cohesive strength of the mortar matrix combined with the flexibility and elasticity of the polymer help to counteract or mitigate the initiation of microcracks. Investigation of the effect of latex powder dosage on the strength of thermal insulation mortar reveals that the tensile bond strength increases with increasing latex powder content, while the flexural and compressive strengths decrease to some extent as the latex powder dosage rises; nevertheless, these properties still meet the requirements for exterior wall finishes.
The bond strength of latex-modified cement mortar at 28 days increases with increasing latex powder dosage. As the latex powder content rises, the bonding performance between the mortar and existing cement-concrete surfaces improves, thereby ensuring its unique advantages when used for repairing cement-concrete pavements and other structural elements. Moreover, the flexural-to-compressive strength ratio of the mortar increases with higher latex powder content, indicating enhanced surface flexibility. It is also observed that, as the latex powder dosage increases, the elastic modulus of the mortar initially decreases and then increases. Overall, with increasing polymer-to-cement ratio, both the elastic modulus and the deformation modulus of the mortar are lower than those of conventional mortar.
The variation in latex powder dosage has a very significant impact on the flexural strength of geopolymer mortar. When the latex powder content is 3%, 6%, and 10%, the flexural strength of fly ash–metakaolin-based geopolymer mortar increases by factors of 1.8, 1.9, and 2.9, respectively. Moreover, the deformation-resistance capacity of the fly ash–metakaolin-based geopolymer mortar increases with increasing latex powder content. At latex powder dosages of 3%, 6%, and 10%, the flexural toughness of the fly ash–metakaolin-based geopolymer mortar increases by factors of 0.6, 1.5, and 2.2, respectively.
SAE latex powder significantly enhances the flexural and bond tensile strengths of cement mortar, thereby improving its flexibility and increasing the bond tensile strength at the interface between cement mortar–concrete and cement mortar–EPS board systems.
When the polymer-to-cement ratio is between 0.3 and 0.4, the fracture elongation of polymer-modified cement mortar increases sharply from less than 0.5% to nearly 20%, thereby transforming the material from rigid to flexible. Further increasing the polymer content can yield even superior flexibility.
Increasing the dosage of latex powder in mortar can enhance its flexibility. When the polymer content is around 15%, a significant change in mortar flexibility is observed; beyond this dosage, the degree of improvement in flexibility increases markedly with further increases in latex powder content.
Bridge-crack-bridging capacity and transverse-deformation tests reveal that, as the latex-powder dosage increases from 10% to 16%, the flexibility of the mortar progressively improves: the dynamic bridge-crack-bridging capacity (at 7 days) rises from 0.19 mm to 0.67 mm, while the transverse deformation (at 28 days) increases from 2.5 mm to 6.3 mm. In addition, it is observed that increasing the latex-powder content slightly enhances the impermeability pressure on the back face of the mortar and reduces its water absorption. However, with further increases in latex-powder dosage, the mortar’s long-term water resistance gradually declines. By optimizing the latex-powder content within the range of 10% to 16%, the modified cement-based slurry can achieve both excellent flexibility and outstanding long-term water resistance.