Reuse of Oil Refining Sludge Residue Ash via Alkaline Activation in Matrices of Chamotte or Rice Husk Ash

The aim of this work is to investigate the possibility of reusing ashes obtained by the calcination of industrial sludge from the oil refining industry (ORSA) as a secondary raw material in the manufacture of alkaline activated cements or geopolymers. The incorporation behavior of 5–20 wt.% of residue in binary mixtures with rice husk ash (RHA) or chamotte (CHM) was evaluated. The cements were activated with a sustainable alternative activating solution obtained from NaOH (10 M) and diatomaceous earth. The specimens were cured at room temperature. Physical and mechanical properties were determined, and the reaction products were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM-EDX). The results indicate that the addition of ORSA (5–20 wt.%) to RHA and CHM improves the mechanical strength of alkaline activated cements with maximum compressive strengths of 30.6 MPa and 15.7 MPa, respectively, after 28 days of curing, with the incorporation of 20 wt.% waste. In these mixtures, the sludge acts as a source of aluminum, promoting the formation of a higher amount of geopolymer gel N-A-S-H in materials using RHA as a precursor and also (N)-(C)-A-S-H gel in cements using CHM.