# Effect of Polycarboxylate Admixture on the Performance of Fluorogypsum-Based Self-Leveling Material
## 3 Results and Discussion  
### Setting Time and Fluidity  
Figure 3a illustrates the impact of PCE on the setting time of FSLM. The results indicate that PCE has a noticeable effect on delaying the setting of the plaster, with the setting time increasing as the superplasticizer dosage increases. Specifically, when the superplasticizer dosage was 0.2%, the initial setting time extended to 330 min, and the final setting time reached 450 min, which were 4.5 and 2.8 times longer than the blank group, respectively. This effect can be attributed to the complexation between the carboxylic group of the superplasticizer and the calcium ions of gypsum, as well as the chemisorption on the nucleation clusters. As the concentration of the superplasticizer increases, the adsorption of gypsum crystals on the superplasticizer also increases, thereby hindering the formation of gypsum crystals [33; 37]. In summary, the alteration in setting time can be attributed to the modification of the crystallization rate of gypsum crystals by PCE [29].  
Figure 3b presents the trends of initial slump, 30 min slump, and 30 min slump loss of FSLM with PCE doping. It can be observed that the group doped with 0.08% PCE exhibits no fluidity at a water-cement ratio of 0.24, with a 30 min slump of 57 mm. As the superplasticizer dosage increases, the adsorption of the superplasticizer on the surface of gypsum particles increases, resulting in increased inter-particle bilayer repulsion and enhanced fluidity. When the superplasticizer dosage reaches 0.14%, the 30 min slump of the plaster increases to 142 mm. Further increasing the superplasticizer dosage to 0.2% leads to a 30 min slump of 159 mm for the plaster. For PCE dosages of 0.08%, 0.11%, 0.14%, 0.17%, and 0.20%, the 30 min slump losses of the samples are 25 mm, 16 mm, 4 mm, 3 mm, and 1 mm, respectively. The improvement effect of PCE on 30 min slump loss strengthens with increasing dosages. This is because PCE possesses a comb-like molecular structure, and its dispersion effect is primarily achieved through the spatial dislocation effect provided by its long side chains. As a result, the fluidity of gypsum plaster is enhanced, and the plaster's fluidity loss is reduced while improving dispersibility [22; 38]. When combined with the effect on the setting time, the dispersion mechanism of PCE on gypsum powder is realized by influencing the setting time and hydration reaction between gypsum and water [39]. The higher the PCE admixture, the greater the adsorption on the surface of anhydrous gypsum, resulting in higher fluidity and better dispersion retention of the plaster.  
The dashed line in Figure 3b represents the baseline requirement for the 30 min slump of gypsum-based self-leveling mortar according to JC/T 1023-2021. It can be observed that the 30 min slump of FLSM samples meets the standard requirement when the PCE admixture is \(\geq\)0.14%. Additionally, as the superplasticizer reaches 0.14%, the initial slump of the plaster shows a lesser tendency to increase with the increase in superplasticizer dosage, indicating that the appropriate PCE dosage is 0.14%.