Fabrication of thermal insulation geopolymer bricks using ferrosilicon slag and alumina waste

The present study introduces the preparation of thermal insulation geopolymer bricks using ferrosilicon slag and alumina waste. Compressive strength, bulk density, cold and boiling water absorption, apparent porosity, thermal conductivity, and Fourier-transform infrared spectroscopy were used to characterized the geopolymer bricks. Ferrosilicon slag suffers from low alumina content. Thus, alumina is added to compensate for this deficiency. Pristine ferrosilicon slag and the SiO2/Al2O3 (Si/Al, ratio = 2) sample were prepared at different NaOH concentrations (i.e., 6, 8, 10, and 12 M; Na2SiO3/NaOH ratio = 2.5), different curing times (i.e., 3, 7, 14, and 28 days), and room temperature. The 8 M NaOH concentration achieved the best compressive strength. Accordingly, different Si/Al ratios were prepared and tested at 8 M NaOH, room temperature, and different curing times (i.e., 3, 7, 14, and 28 days). Results indicate that increasing the alumina content enhances the geopolymer properties but reduces the compressive strength of the prepared geopolymer. The sample with Si/Al ratio = 1 exhibited a higher compressive strength (10.9 MPa) than the other Si/Al ratios (i.e., 4, 3, 2, and 0.5) and the pristine ferrosilicon slag after 28 days of curing and at 8 M NaOH. The obtained value is consistent with the ASTM C62 and Egyptian standards. Furthermore, the addition of alumina waste decreased the thermal conductivity of the prepared geopolymer bricks.