# Effects of Water-Reducing Agents on the Mechanical Properties of Foamed Phosphogypsum
## 1 Introduction  
Phosphogypsum is a by-product of phosphate fertilization. According to statistics, approximately 4-6 tons of phosphogypsum are produced from 1 ton of phosphoric acid. This large amount of phosphogypsum occupies land resources and causes pollution to the surrounding environment, seriously restricting the green development of the phosphate industry. Therefore, the resource utilization of phosphogypsum has become the focus of the Government and the phosphate industry [1; 2; 3; 4; 5; 6; 7; 8]. Paper gypsum boards are one of the main absorption media of phosphogypsum. When phosphogypsum is used as the gypsum base raw material in paper gypsum boards, it can alleviate the pressure of efficient resource utilization for phosphogypsum and solve the shortage problem of gypsum resources. Therefore, under current green, low-carbon, and other strict environmental requirements, it is of great significance to carry out the research and production of phosphogypsum paper boards [9; 10; 11]. Phosphopypsum paper boards are mainly composed of a phosphogypsum board core and a protective paper [12; 13; 14]. During the preparation of gypsum board cores, to save production energy consumption and reduce cost, water-reducing agents are often added to ensure that gypsum slurries keep a certain fluidity with reduced water consumption [15; 16; 17; 18; 19; 20]. Moreover, the decrease in the water consumption of gypsum slurries increases their surface density; thus, foaming agents are used to reduce the surface density of gypsum boards [21; 22; 23; 24; 25; 26; 27]. Water-reducing agents and foaming agents are indispensable raw materials in the production of paper gypsum boards. Superplasticizers and foam are highly active organic materials. When they work together in gypsum slurries, strong chemical interactions occur between them. If the degree of interactions between them is small, they manifest little influence on the macro-performance of the gypsum board core. On the contrary, if the interaction degree is strong, they yield an adverse effect on the macro-performance of the gypsum board core. [PERSON], [PERSON] et al. [28] analyzed the interaction between the foaming agent and the water-reducing agent for deslufurized gypsum and found that the effect of the foaming agent on 0.3% of FDN was less than that on 0.1% of PCE. Although the effects of foaming agents on water-reducing agents are considered during the preparation of gypsum slurries, the influences of water-reducing agents on the formation and distribution of foam are generally neglected, causing the poor stability of paper gypsum boards [29; 30]. [PERSON], [PERSON] et al. [31] studied the compatibility between different water-reducing agents and phosphogypsum-based cementitious materials, including the dependence of mechanical properties and rheological properties. The test results showed that the FDN has strong compatibility with the gypsum-based cementitious materials of phosphorus buildings. [PERSON], [PERSON] et al. [32] studied the effects of polycarbonate acid and sulfonated melamine superplasticizer on the fluidity, setting, and dry compression strength of phosphogypsum; the results showed that the 0.48% dosage of polycarbonate acid was more suitable for phosphogypsum. However, in these studies, foamed phosphogypsum was not considered. [PERSON], [PERSON] et al. [33] studied the effects of hydroxypropyl methyl cellulose ether (HPMC) on the rheological properties, pore structure and mechanical properties of EPS-phosphorus gypsum composite paste. The results showed that, with the increase in HPMC content, the yield stress and plastic viscosity of paste increase gradually and that the pore structure and mechanical properties of gypsum paste are improved. The optimum HPMC content for EPS-phosphorus gypsum composite slurry is 0. 20%. [PERSON] [34] focused on the preparation of foamed phosphogypsum and the effect of silicone on the properties of foamed phosphogypsum.