Spent fluid catalytic cracking catalyst (FCC) as a viable substitute for enhancing low-grade kaolinite clays in LC3 systems

Abstract

Limestone Calcined Clay Cement (LC3) is a promising alternative to Ordinary Portland Cement (OPC) for reducing CO2 emissions. However, the widespread availability of high-quality kaolinitic clays required for its production is limited. This study investigates the enhancement of LC3 mixtures using a low-grade calcined kaolinitic clay (L-CC), with the employment of a waste derived from the petrochemical industry. In this context, this waste is a silicoaluminous material denominated spent fluid catalytic cracking catalyst (FCC). The L-CC was partially replaced (doped process) with FCC at 6%, 10%, and 15% by weight. The pozzolanic reactivity, hydration kinetics, phase evolution, and mechanical properties of the mixtures doped with FCC were evaluated and compared against control LC3 mixture made with a high-grade calcined kaolinitic clay (H-CC). Here, the R3 test was used to characterise the reactivity of both calcined clays and FCC. Thermogravimetric analysis (TGA) and X-ray diffraction (XRD) confirmed that FCC addition enhanced pozzolanic activity, leading to a greater portlandite consumption and the formation of additional C-(A)-S-H and AFm phases. Consequently, compressive strength improved with increasing FCC content. After 28 curing days, the mortar containing 6% FCC achieved a 21.2% improvement in compressive strength compared to the non-doped LC3 system. At the same curing ages, the improvements in the mortars with 10% and 15% of FCC were 33.7% and 58.3% respectively. These values confirmed the potential of waste FCC to improve mixtures with low-grade calcined kaolinitic clays.