# Properties of Foamed Lightweight High-Performance Phosphogypsum-Based Ternary System Binder
## 2 Materials and Methods  
Dihydrate phosphogypsum (CaSO\({}_{4}\):2H\({}_{2}\)O) analyzed in this work is a waste generated by fertilizer production plant AB Lifosa (Kedainiai, Lithuania) in wet-process phosphoric acid production, where apatite from the Kovdor mine, Kola peninsula, Russia, is decomposed by sulphuric acid. To produce 1t of orthophosphoric acid, about 3.0-4.5 t of PG is obtained [16]. At the enterprise, volcanic origin Cola apatite (Kirov and Kovdor) (containing F\({}_{2}\) 1-2%, P\({}_{2}\)O\({}_{5}\)--about 38% as phosphorus) is used as a raw material in the production of phosphoric acid. Besides, phosphorites of sedimentary origin from other countries (Morocco, Jordan, Kazakhstan (Karatau), Algeria, South Africa Republic) are used. The dihydrate PG was used as secondary raw material in the present research. Chemical composition of raw materials is given in Table 1. The initial pH of PG is in the range from 2.2-2.9 while during the storage it can increase gradually. The PG was dried at 60 \({}^{\circ}\)C (moisture content 9-12 wt.%) and milled to powder-like particles with collision milling in semi-industrial disintegrator with the rotational speed of 50 Hz. The particle size distribution is given in Figure 1. Then, the calcium sulfate hemihydrate binder was obtained by treatment of milled gypsum powder at temperature 180 \({}^{\circ}\)C for 4 h. Commercial gypsum plaster (BG) was used to compare the characteristic technological properties of obtained binder. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Element** & **Commercial Gypsum BG** & **Phosphogypsum PG** & **Metakaolin MKW** & **Cement CEM I 42.5N** \\ \hline SiO\({}_{2}\) & 3.73 & 1.07 & 51.80 & 22.64 \\ Al\({}_{2}\)O\({}_{3}\) & 1.68 & 0.70 & 34.20 & 5.93 \\ Fe\({}_{2}\)O\({}_{3}\) & 0.46 & 0.22 & 0.50 & 3.26 \\ CaO & 35.64 & 37.16 & 0.10 & 57.04 \\ MgO & 3.92 & 0.21 & 0.10 & 4.26 \\ SQ\({}_{3}\) & 30.90 & 37.38 & - & 3.30 \\ Na\({}_{2}\)O & 0.31 & 0.48 & 0.60 & 0.10 \\ K\({}_{2}\)O & - & - & - & 2.40 \\ TiO\({}_{2}\) & 0.05 & 0.11 & 0.60 & 0.38 \\ Cl & - & - & - & 0.14 \\ P\({}_{2}\)O\({}_{5}\) & - & 0.57 & - & 0.46 \\ LOI & 22.43 & 19.24 & 11.5 & - \\ Total & 99.42 & 99.74 & 99.60 & 99.90 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Chemical composition of raw materials used to prepare novel building material [weight %]. Figure 1: The particle size distribution of the raw materials used to prepare novel building material. The other components of the binder were metakaolin as supplementary cementitious material and Portland cement CEM I 42.5N (CEM). Chemical composition of CEM is given in Table 1. The initial setting time was 182 min and the final setting was 224 min (according to LVS EN 196-3); the normal consistency was 28.2% (according to LVS EN 196-3). Blaine fineness of cement was 3787 cm\({}^{2}\)/g (according to LVS EN 196-6). Na equivalent was 1.68. Compressive strength after 1 day was 15.4 MPa, after 2 days--32.9 MPa, after 7 days--48.8 MPa, and after 28 days--60.5 MPa. Waste metakaolin (MKW) was obtained from the porous glass granule production factory \"Stiklporas\" JSC (Druskininkai, Lithuania). Metakaolin is a by-product from the final stage of expanded glass granule production, where kaolinite clay powder is used as a substance for anti-agglomeration and is heated at 850 \({}^{\circ}\)C temperature for 40-50 min. MKW is mostly amorphous dehydration product of kaolinite, Al\({}_{2}\)(OH)\({}_{4}\)Si\({}_{2}\)O\({}_{5}\), which exhibits strong pozzolanic activity often used in the concrete industry as a supplementary cementitious material. XRD pattern and detailed description of MKW was published before [17]. MKW contains amorphous metakaolin detected in 20 region from 15 to 30\({}^{\circ}\), and some minor crystalline phases were also detected in MKW: quartz (SiO\({}_{2}\)) and Halloysite Al\({}_{2}\)Si\({}_{2}\)O\({}_{5}\)(OH)\({}_{4}\). The specific surface area of the MKW is 15.86 m\({}^{2}\)/g. Loss of ignition for metakaolin was 11.5%.