Influence of milling of a reused FCC catalytic waste on the early hydration stages of a special class cement

This work investigates the influence of milling on the physical, chemical and mineralogical properties of a catalyst residue (Recat) after being reused in a second Fluid Catalytic Cracking process (FCC). The effect of milling this waste in a planetary ball mill for different times on the hydration process is also evaluated as partial replacement of a special cement for oil wells. Six pastes were prepared, one for reference and five others containing Recat milled for different times, replacing the cement mass by 15%. The water/solids ratio remained constant and equal to 0.5. The hydration process was evaluated by isothermal calorimetry during the first three days of hydration. The characterization of the pastes at the end of this period was done by thermogravimetric analysis (TG/DTG), X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). The results showed that the milling of Recat improves its reactivity in cementitious pastes, favoring not only pozzolanic activity, but also nucleating action. It was noticed that nucleating and pozzolanic effects occur simultaneously and, that thermogravimetry actually shows only the resulting effect on CH content. As a consequence, when the paste was composed by the less milled Recat, their pozzolanic action during the first three days was higher than their nucleating effect and the opposite was noticed in the pastes prepared with most milled Recat. This was only possible to detect analyzing by thermogravimetry all the pastes also after 28 days of hydration, when the pozzolanic action of the finest Recat particles overcame their early age nucleating effect.