Strength Properties of Phosphogypsum Based Composite Filling Materials

The experimental research of new composite filling cementitious materials that could replace the cement has been carried out, which uses the phosphogypsum as the basic material, the lime, slag powder and other solid waste as auxiliary materials. The researchers use the orthogonal experiment to study the role of phosphogypsum addition for the strength of new composite filling cementitious materials. The strength rule function of new composite filling cementitious materials was obtained based on the phosphogypsum by genetic programming. The regression function was optimized using the genetic algorithms. Though analysing the hydration mechanism of the new composite filling cementitious materials by SEM and XRD, the C-S-H gel and ettringite are turned out as the mainly hydration products. The results are shown: the ettringite and brushite are mainly hydration products of the new composite filling cementitious materials. Comparing with the contrast test of cement, the hydration products of new composite filling cementitious materials based on the phosphogypsum have more ettringite than cement. With increasing of curing time, the hydration products are growing and constantly filled in the pore. Sodium hydroxide is added to accelerate the speed of hydration, and enhance the filling body age compressive strength. The strength of new composite filling cementitious materials based on the phosphogypsum can meet the requirement of Jinchuan Mine when the content of lime is 4.48%, phosphogypsum is 32.42%, glauber is 2.35%, sodium hydroxide is 2.5% and slag powder is 58.3% respectively.