Effect of spent waterglass foundry sand on the performance of MgO-activated slag materials

Spent waterglass foundry sand (SwFS) is a bulk waste of the metallurgical industry containing at least 2-5 wt% of the waterglass layer without effective utilization. To this end, this paper proposes the disposal of SwFS as fine aggregates for MgO-activated slag materials (MASMs). Two types of SwFS subjected to different treating temperatures (100 degrees C and 800 degrees C) were prepared to investigate their effects on fluidity, compressive strength, pore structure, and micromechanical properties of MASM. The experimental results showed that the coated waterglass of SwFS played an important role in affecting the performance of MASM mortars. For SwFS subjected to 100 degrees C, the coated waterglass could be partially dissolved and released into the surrounding paste to activate slag along with MgO. Compared with the group without SwFS, the resulting compressive strength (MPa) of mortars with SwFS was increased by 33.6-74.1% at all ages, and the average elastic moduli (GPa) of C-A-S-H were increased by 19.6%. In contrast, for SwFS subjected to 800 degrees C, the coated waterglass can hardly be dissolved, which induced a complex interface in the microstructure of mortars, leading to the reduced compressive strength of mortars.