Effect of milled fluidised bed cracking catalyst waste on hydration of calcium aluminate cement and formation of binder structure

Abstract

This study analyses the effect of fluidised bed cracking catalyst (FBCC) waste, milled to nano-sizes and unmilled, on the hydration of calcium aluminate cement after hardening under normal conditions and after thermal treatment of the samples at 1200 °C. Differential thermal analysis (DTA), X-ray analysis (XRD), and electron scanning microscopy analysis (SEM) were conducted. Results of calorimetry studies showed that milled FBCC added up to 5% slightly slows down the hydration processes of aluminate cement, whereas 10% of FBCC accelerates the hydration. The total amount of heat released in the samples with milled FBCC was lower than that in the samples with unmilled FBCC. The thermogravimetry analysis (TG) revealed higher mass loss in samples with unmilled FBCC. Additionally, XRD results after hardening showed that, compared to the samples with unmilled FBCC, the samples with milled FBCC yielded a higher relative intensity of unreacted minerals of cement. After burning the samples at 1200 °C, anorthite crystals were formed in the samples with FBCC. The effect of unmilled FBCC on the hydration process was explained by the ability of the particles to absorb water at the initial hydration stage and subsequently to transfer it to further hydration steps, thereby promoting the formation of crystallohydrates in larger quantities.