Impact of incorporating spent oil filtering earths into the formulation of alkali-activated cements based on electric arc furnace slag

In this study an investigation of the effect of incorporating spent oil filtering earths (SOFE) as a precursor in the manufacture of alkaline activation cements based on electric arc furnace slags (EAFS) has been carried out. SOFE were mixed up to 50 wt% with EAFS at 10 wt% intervals. As a control, a binder containing only EAFS was manufactured. The fresh binder samples were cured at room temperature for 7 and 28 days. Phase analysis was conducted using X-ray Diffraction (XRD), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and Scanning Electron Microscopy-Energy Dispersive X-ray spectroscopy (SEM-EDS). The results indicated that the addition of SOFE caused a delay in the geopolymerization or alkaline activation reactions, which resulted in a decrease in mechanical properties at low hydration times, 7 days. However, substitution of SOFE led to an improvement in physical, mechanical, and thermal properties after 28 days of curing. Ideal substitution ratios were 30 wt% or higher. At optimum substitution ratios, the bulk density of alkaline-activated cements decreased, water absorption and total porosity increased, but conversely, flexural and compressive strengths raised from 8.3 MPa and 19.3 MPa, respectively, for control cements to 11.3-11.8 MPa and 24.5-25.7 MPa for cements that incorporated 30-50 wt% SOFE. The increase in mechanical properties could be attributed to the synergistic formation of a hybrid N,C-A-S-H gel, resulting from the higher formation of N-A-S-H geopolymeric gel in comparison to C-A-S-H gel, owing to the higher amount of silica in the SOFE residue. The insulating capability of the cements improved as increasing amounts of SOFE residue were incorporated, with values ranging from 0.68 W/mK for the control binders to 0.34-0.15 W/mK for the cements that included 30-50% by weight of SOFE. The results of this study may help to promote the application of SOFE in the production of more environmentally friendly EAFS-based alkaline activation cements.