Abstract
Cement production is a significant contributor to global CO2 emissions, necessitating the development of alternative construction materials. While ground granulated blast furnace slag (GGBS) and fly ash (FA) have been explored as potential substitutes, their limited availability has prompted the search for new solutions. Current cement production processes, such as calcining, continue to emit substantial amounts of CO2 and consume high levels of energy, exacerbating environmental concerns. This study explores the activation of alternative, waste-derived materials, specifically SCOTBRO’s wash plant filter cake and kaolin using ultra-high shear and hybrid activation techniques to produce high-performance geopolymer mortars.A comprehensive review of emerging opportunities in low-temperature processing and hybrid techniques for feedstock activation in the context of sustainable construction materials demonstrates significant promise for the approach. Therefore, two activation routes were systematically investigated: (i) ultra-high shear mechanical activation (ball milling without additives), and (ii) hybrid activation (mechanochemical activation via ball milling with NaOH). Both uncalcined and calcined SB filter cake samples, alongside kaolin, were subjected to varied milling durations (1, 10, 30, and 60 min) and subsequently characterised using XRD, FTIR, SEM-EDX, particle size distribution, and surface area analyses. Compressive strengths of geopolymer mortars were measured at 7 and 28 days and correlated with material reactivity and microstructural evolution.
The results reveal promising results to produce alternative activation methods for using waste derived filter cakes as primary feedstock materials for low cement construction. The results demonstrate that hybrid activation significantly improved reactivity and compressive strength, overcoming the diminishing returns caused by particle agglomeration observed in prolonged mechanical activation. Uncalcined filter cake treated via hybrid activation achieved a 136% increase in compressive strength (14.74 MPa at 28 days), while calcined hybrid-activated samples reached 30.89 MPa at 28 days, comparable to benchmark SCMs. Optimal milling durations of 10–30 min was identified as critical for balancing amorphization, particle refinement, and avoidance of agglomeration. These findings establish hybrid activation as an effective method for producing high-performance geopolymer precursors from low-reactivity industrial wastes.
From a sustainability perspective, this research demonstrates the global potential of hybrid activation as a scalable and economically viable method for transforming an otherwise landfill-bound industrial waste into a value-added construction material. The hybrid activation approach directly supports international circular economy frameworks by reducing reliance on Portland cement, significantly lowering CO₂ emissions, and decreasing the environmental burden of industrial waste disposal. Furthermore, it contributes to the achievement of multiple UN Sustainable Development Goals (SDGs 9, 11, 12, and 13), offering a transformative pathway for industrial symbiosis and decarbonisation of the built environment.
Overall, this study establishes a novel and technically robust activation methodology that addresses the dual global challenges of climate change mitigation and resource efficiency. The findings provide a strong foundation for large-scale industrial adoption of geopolymer technology derived from SB filter cake, with recommendations for future work including pilot-scale production, durability testing, and techno-economic feasibility studies to enable implementation at a global level.
| Date of Award | 15 Oct 2025 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | David Hughes (Supervisor) & Emeka Amalu (Supervisor) |