Effect of phosphogypsum on the stability upon firing treatment of alkali-activated slag

The paper analyses the preparation of alkali-activated slag with phosphogypsum additive. The specimens of alkali-activated slag were tested both at room and at elevated temperatures. It was determined that phosphogypsum shortened the setting times of alkali activated slag mixture cured at room temperature. During hydration process sodium sulfate formed in alkali activated specimens. Compressive strength depends on phosphogypsum amount too. The highest compressive strength MPa of specimens was with 5% of phosphogypsum. Similar situation was after exposure elevated temperatures. The inclusion of 5% phosphogypsum showed the optimum content in which higher residual strength was obtained after being treated at 400, 600, 800 and 1000 °C temperatures. These type specimens exhibited approximately an average of 1.2 times greater residual strength than specimens without phosphogypsum. This means that alkali-activated slag blended with phosphogypsum have great potential applications for fire resistance. It is possible to recycle phosphogypsum in alkali activated slag blends.