Effect of Redispersible Latex Powder on the Properties of Thick-Set Gypsum-Based Self-Leveling Mortar
Release Time:
2020-02-28
Source:
Redispersible latex powder is a crucial admixture that significantly influences the performance of thick-layer gypsum-based self-leveling mortars. This study investigates the impact of redispersible latex powder on the physical and mechanical properties of such mortars and, through microstructural analysis, elucidates the mechanisms by which it enhances their mechanical performance, thereby demonstrating the substantial role of redispersible latex powder in gypsum-based self-leveling systems.
Redispersible latex powder is a crucial admixture that significantly influences the performance of thick-layer gypsum-based self-leveling mortars. This study investigates the impact of redispersible latex powder on the physical and mechanical properties of such mortars and, through microstructural analysis, elucidates the mechanisms by which it enhances their mechanical performance, thereby demonstrating the substantial role of redispersible latex powder in gypsum-based self-leveling systems.
Redispersible latex powder is a widely used organic binder that, when incorporated into gypsum-based construction materials, can enhance product performance. Experimental results show that the initial flowability of thick-layer gypsum-based self-leveling mortar first increases and then decreases with increasing latex powder dosage. This phenomenon arises because latex powder, upon dissolution in water, imparts a certain degree of viscosity; at lower dosages, the increase in slurry viscosity enhances its ability to suspend fillers, thereby promoting flow. However, as the latex powder dosage continues to rise, the further increase in slurry viscosity leads to greater internal cohesion, resulting in a decline in flowability. Notably, the latex powder dosage has virtually no effect on the 20-minute flowability of the mortar.
As an organic binder, the strength development of latex powder depends on the evaporation of water from the slurry, with film formation ultimately contributing to bond strength. However, after 24 hours of placement, thick-layer gypsum self-leveling mortar still retains a relatively high moisture content, preventing the latex powder from fully developing its strength; consequently, the 24-hour strength of gypsum-based self-leveling mortar decreases as the latex powder dosage increases. At a latex powder dosage of 2.0%, the 24-hour flexural and compressive strengths of the mortar decrease by 25.5% and 11.9%, respectively, compared with the control mix without latex powder. Once the moisture has completely evaporated under oven-dry conditions, the latex powder forms a continuous film, resulting in improved bonding performance; accordingly, the oven-dry strength of the gypsum-based self-leveling mortar increases with increasing latex powder dosage. At a latex powder dosage of 2.0%, the oven-dry flexural and compressive strengths of the mortar are 63.5% and 36.8% higher, respectively, than those of the control mix without latex powder.
In gypsum-based self-leveling mortar without latex powder, numerous rod-like and columnar dihydrate gypsum crystals are interspersed with irregular fillers. These dihydrate gypsum crystals interlock with one another and also with the fillers, packing together in an irregular yet dense manner to develop strength in the mortar. When 2.0% redispersible latex powder is incorporated, the latex powder forms filamentous connections within the mortar, creating organic bridges between dihydrate gypsum crystals and between crystals and fillers. An organic film forms on the surface of the dihydrate gypsum crystals, enveloping and bonding the interlocking regions among the crystals, thereby enhancing the mortar’s cohesion and bond strength and increasing its overall strength. The latex powder exhibits film-forming properties in the mortar, which improve both the cohesion and bond strength of the dried mix. The film formed by the latex powder at the interfaces between dihydrate gypsum crystals and fillers provides effective adhesion between the crystals and among the fillers, boosting the cohesion at these interfaces and, consequently, the overall bond strength of the gypsum-based self-leveling mortar. At a latex powder dosage of 2.0%, the bond strength of the mortar increases by 46.5% compared with the unreinforced formulation.
Thick-layer self-leveling cement adjusts the performance of desulfurization gypsum or phosphogypsum by incorporating redispersible latex powder and uses industrial waste as aggregate, thereby making full use of industrial slag. This approach delivers both economic benefits and significant social benefits.
