Flow ability of cemented paste backfill with high-volume industrial wastes

• Sustainable CPB flowability achieved with high-volume slag and fly ash. • Yield stress and viscosity reduced with up to 80% binder replacement. • Response surface methodology optimized CPB rheological properties. • Microstructural analyses identified C–S–H–dominated hydration in slag–FA binders. • Optimized mix achieves >90 % slag–FA reuse, advancing sustainable mine backfilling. This study investigates the rheological properties of cemented paste backfill (CPB) incorporating high-volume slag and fly ash (FA) as sustainable substitutes for Portland cement type I (PCI). The research aims to enhance CPB flowability while maximizing the reuse of industrial byproducts. Rheological tests were conducted on CPB samples composed of silica tailings with varying PCI/slag/FA ratios to assess their effects on yield stress and viscosity. Using a central composite design and response surface methodology, mathematical models were developed to quantify and predict the relationships between rheological parameters and binder composition. Microstructural and monitoring analyses revealed that slag and FA influence CPB flowability through particle size, shape, and hydration characteristics. Results indicate that replacing up to 80 % of PCI with slag and FA reduces yield stress and viscosity by 4.2 %–21.7 % and 0.7 %–5.0 %, respectively, improving flowability for mine filling applications. However, excessive slag and FA contents (90 %) increase fine particle interactions, elevating yield stress and viscosity. Time-dependent rheological changes were observed, with yield stress and viscosity increasing by 40 %–66.7 % and 3.9 %–7.1 % during two hours of curing, driven by hydration product formation. The optimal binder ratio (10.15 % PCI, 20.3 % slag, and 79.7 % FA) achieves a desirable balance of low yield stress (137.4 Pa) and viscosity (2.91 Pa·s) with over 90 % industrial waste reutilization. This study provides a robust framework for optimizing CPB formulations, addressing key challenges in sustainable mining practices, and guiding the large-scale reuse of industrial wastes.