Optimisation of hydraulic lime mortars incorporating an oil-refinery catalyst by-product for sustainable building rehabilitation

ABSTRACT This investigation employs a Central Composite Design-based Design of Experiments (DoE) methodology to develop hydraulic lime mortars incorporating equilibrium catalyst (ECat), a by-product generated at the fluid catalytic cracking unit in oil refineries. The derived mathematical models describe the quantitative effects of key mixing variables, specifically ECat content, water-to-binder ratio and water repellent dosage, as well as their cross-interactions, on mortar properties, namely workability, compressive strength, ultrasound propagation velocity and dynamic modulus of elasticity. Numerical optimisation techniques enabled the identification of optimal lime mortar compositions that maximise eco-efficiency while ensuring compliance with both regulatory and technological requirements for diverse masonry applications, including the rehabilitation of ancient buildings. Results confirm the by-product upcyclability of ECat, with feasible incorporation levels up to 56.6% by mass, yielding mortars with significant potential for reducing the environmental impact of the built environment while advancing the circular economy and fostering technological innovation in the construction sector.