Investigation on rapid solidification of waste dredged sludge with magnesium phosphate cement modified by GGBFS

Abstract

The main concern of this paper is to understand the influences of industrial by-products ground granulated blast furnace slag (GGBFS) on the properties of waste dredged sludge solidified by magnesium phosphate cement (MPC), which were determined in terms of the fluidity, setting characteristic, temperature evolution, mechanical properties, spontaneous imbibition, water absorption, electroosmosis, leachate and shrinkage behavior. The obtained results indicated that when the ratio of GGBFS to MgO was 5:5, the GGBFS-modified solidified sludge (SS) had fast setting performance, suitable hydration temperature and good mechanical properties. GGBFS can react with NH4H2PO4 and improve overall performance. Proper amount of slag can significantly improve the unconfined compressive strength (UCS) which was attributed to chemical reaction, filling effect and dilution effect. The imbibition indexes of the SS were approximately linear with the square root of time. Moreover, the microstructure and the hydration products were tested by X-ray diffraction (XRD), scanning electron microscopy (SEM) along with energy dispersive spectrometer (EDS). The experimental results illustrated that the filling effect and reaction of the GGBFS make the structure denser and the skeleton connection strengthened, forming new hydration products such as MgNH4PO4·6H2O, AlPO4, MgHPO4·3H2O, Mg(OH)2, Mg3(PO4)2, (NH4)2Ca(HPO4)2·H2O, Ca(NH4)2·(HPO4)2·H2O, Ca(H2PO2)2.