Binary blended filler of spent fluid catalytic cracking (FCC) catalyst (ECat) and limestone for asphalt mixtures

The asphalt industry faces significant challenges regarding long-term durability, sustainability, with urgent need for decarbonisation. This study focuses on the reuse of a spent catalyst from the fluid catalytic cracking (FCC) unit, known as equilibrium catalyst (ECat), as a constituent of the binary-blended filler with limestone for asphalt mixtures. Since 2019, ECat has been officially classified in Portugal (to the authors’ knowledge, the only country) as a by-product eligible for use in construction materials, supporting its potential valorisation. A comprehensive chemical, geometrical, and physical characterisation revealed that ECat’s aluminosilicate-based composition with an exceptionally high specific surface area promotes a high bitumen number and a high Rigden Voids value. These properties enhance filler-bitumen affinity and mastic cohesion, but cause early stiffening when ECat fully replaces conventional filler. Asphalt mastics incorporating 15–30% ECat-limestone blended filler achieved a balance between stiffness and workability while meeting technical and normative thresholds; 15% is recommended to avoid excessive stiffening. Statistical analyses identified bitumen number, Rigden voids and absorption capacity as dominant predictors of mastic behaviour, enabling predictive models for filler optimisation. ECat allowed a reduction in bitumen content up to 10% without compromising the mechanical behaviour of asphalt mixtures while improving their functional performance. Overall, ECat improves high temperature performance and filler-bitumen interaction, offering a potential scalable circular-economy solution for ECat; field-scale mixture testing and long-term ageing assessments are recommended before widescale implementation. • Spent FCC catalyst (ECat) valorised in binary blend filler for asphalt mastics. • 15% ECat-limestone blended filler maintains workability and meets standards. • ECat-bitumen interaction enhances mastic cohesion and high-temperature performance. • ECat mixtures show similar or improved fatigue, deformation and water resistance. • Use of ECat reduces bitumen content supporting circular economy in asphalt industry.