# Effect of Polycarboxylate Admixture on the Performance of Fluorogypsum-Based Self-Leveling Material
## 1 Introduction  
Gypsum resources primarily comprise natural gypsum and industrial by-product gypsum, including fluorogypsum. Fluorogypsum is generated during the production of hydrofluoric acid. In China, every ton of hydrofluoric acid produces 4-5 tons of fluorogypsum [1]. Its main physical phase is CaSO\({}_{4}\), which contains a small amount of unreacted CaF\({}_{2}\) impurities compared with natural anhydrite. The physical and chemical properties of fluorogypsum vary widely, exhibiting poor hydration and hardening ability, low early strength, and other defects [2]. Because of the low utilization rate [3], a significant amount of fluorogypsum is deposited as solid waste in piles or landfilled. However, some studies have demonstrated that fluorogypsum has a higher potential activity compared to natural anhydrite [4]. In recent years, numerous scholars have effectively stimulated the potential activity of fluorogypsum through various modifications, such as pulverization treatment, various salt excitations [5; 6; 7; 8], and further enhancements using active minerals like slag, fly ash, silica fume, and Portland cement [9; 10; 11; 12; 13; 14]. These modifications have led to the production of high-strength cementitious materials that are more widely used in the field of building materials. For instance, [PERSON] [15] developed a high-strength composite cementitious material using fluorogypsum, slag, and Portland cement. Similarly, [PERSON] [16] and [PERSON] [17] used a fluorogypsum-based cementitious agent to cure sludge. Self-leveling materials, which are now more widely used, can be categorized into cement-based and gypsum-based materials based on their properties [18]. Althoughcement-based self-leveling mortars possess excellent mechanical properties, they are prone to shrinkage and cracking. On the other hand, gypsum-based self-leveling mortars not only offer advantages such as sound and heat insulation, fire resistance, moisture regulation, and resistance to shrinkage and cracking, but they can also reduce carbon emissions by 20% [19; 20]. Numerous studies have demonstrated that gypsum can be utilized to produce self-leveling mortars [21; 22; 23; 24]. For instance, [PERSON] used phosphorus II anhydrous gypsum as the primary cementing material and modified phosphopysum with modified steel slag, \(\beta\)-hemihydrate gypsum, and calcium aluminate cement. The resulting self-leveling mortar was performed in accordance with JC/T 1023-2021 [25; 26]. However, due to the requirements of gypsum-based self-leveling mortar for low fluidity loss over time and high early strength, high-strength alpha-hemihydrate gypsum is primarily used as the cementitious material for gypsum-based self-leveling mortar [27; 28]. In contrast, the poor hydration and hardening ability, low early strength, and poor fluidity of fluorogypsum limit its application in preparing gypsum-based self-leveling mortars. Superplasticizers are crucial admixtures that enhance the fluidity of self-leveling materials under low water-cement ratio conditions. They are widely used in cement-based materials, but it has also been shown that superplasticizers can improve the properties of gypsum-based materials by increasing their fluidity while reducing water consumption and porosity, thereby increasing their strength and water resistance [29; 30; 31]. [PERSON] [32] produced gypsum-based self-leveling mortars by adjusting the polycarbonate admixture (PCE) content to achieve a suitable consistency for self-leveling, using hemihydrate gypsum as raw material. Moreover, compared to other types of superplasticizers, PCE has a less inhibitory effect on the growth and hydration of hemihydrate gypsum crystals [33]. The water reduction rate of hemihydrate gypsum slurry reached 18-20% with a PCE dosage of 0.6%, and the structure of the hardened body was denser, with the compressive strength increasing up to 72% compared to the blank sample [34].