Strength Development of Gypsum-Based Self-Leveling Mortar
Release Time:
2021-07-14
Source:
Self-leveling
The shrinkage of cement-based self-leveling mortar is significantly higher than that of gypsum-based self-leveling mortar; by 28 days, the shrinkage of cement-based self-leveling mortar is approximately 1.17 mm/m. Over time, the shrinkage of cement-based self-leveling mortar increases to about 1.31 mm/m after three months, whereas the shrinkage of gypsum-based self-leveling mortar remains around –0.19 mm/m. In other words, the excessively high shrinkage of cement-based self-leveling mortar makes cracking highly likely; therefore, during actual construction, appropriate curing measures must be implemented for cement-based self-leveling mortar to ensure construction quality.
Intensity development
The strength development of gypsum-based self-leveling mortar is closely related to the degree of drying of the mortar itself. In addition to the crystal water required for the formation of dihydrate gypsum, any excess water remaining in the voids of the mortar will evaporate into the air through the capillary pores, thereby contributing to strength development. In other words, the rate of strength gain is directly proportional to the drying rate of the gypsum-based self-leveling mortar.
Gypsum-based self-leveling mortar not only exhibits high early strength (greater than 6 N/mm² at 6 hours) but also demonstrates rapid strength development over time, reaching more than 30 N/mm² at 28 days.
The bond strength of gypsum-based self-leveling mortar at different curing periods (1 day, 2 days, and 7 days) increases rapidly with the extension of the curing period. For example, the 28-day bond strength rises from 0.8 N/mm² (measured after 1 day) to 1.4 N/mm² (measured after 7 days), representing an increase of approximately 35%.
In other words, for gypsum-based self-leveling mortar, an extended drying time promotes the development of its inherent strength; however, under the same conditions, cement-based self-leveling mortar exhibits significantly superior early-age bond strength compared with gypsum-based self-leveling mortar.
Thermodynamic Properties
Gypsum-based self-leveling mortar remains essentially stable at 50°C, with no significant further changes; for example, its shrinkage values and compressive strength at 28 days and 194 days are virtually identical. This demonstrates that gypsum-based self-leveling mortar is particularly well suited for underfloor heating systems.
