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<p>Incorporating oily sludge ash (OSA) into fly-ash based geopolymers addresses environmental disposal issues and enhances sustainability. Geopolymer mortars were synthesized to identify the optimal alkali activator ratio. Thereafter, OSA content (0–10%) were incorporated to explore the effects on some technical properties of the mortar. Compressive and flexural strengths were measured at 7, 14, and 28 days, and durability was assessed via water absorption; microstructural properties were analysed by X-ray Fluorescence (XRF), Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDX) and Fourier Transform Infrared Spectroscopy (FTIR). The geopolymer with 35% NaOH and 65% Na₂SiO<sub>3</sub> had the optimal alkali activator ratio as evident by the compressive and flexural strengths of 30.98&#xa0;MPa and 5.90&#xa0;MPa, respectively. Incorporating 2.5% OSA into this mix further improved densification and strength, but higher replacements (5 − 10%) reduced strength due to excess unreacted carbon and alkali imbalance. XRF indicated OSA contains high CaO (33.9%) and Fe₂O₃ (25.4%), complementing the SiO₂ (47.2%) and Al₂O₃ (17.4%) of fly ash. SEM-EDS of the optimal geopolymer revealed well-dispersed angular OSA particles filling voids and major binder elements (Oxygen:42%, Carbon:34% and Silicon: 9%), confirming aluminosilicate gel formation. FTIR spectra exhibited a dominant Si–O–Si/Al band (1009&#xa0;cm⁻¹) and no characteristic petroleum-hydrocarbon peaks. Cradle-to-site life cycle analysis showed that fly ash and OSA contribute &lt; 1% to the composite’s embodied carbon, yielding a very low carbon footprint. Peak eco-strength efficiency of 0.107&#xa0;MPa/ (kg CO₂/kg)) was obtained at 2.5% OSA, demonstrating that moderate OSA additions improve structural performance relative to emissions.</p>

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Mechanical and sustainability assessment of the influence of oily sludge ash on fly ash-based geopolymer composites

  • 期刊论文

  • 发表日期：

    2025年7月28日

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  • Tharshini Suriya Kumar,
  • Abiola Usman Adebanjo,
  • Nasir Shafiq,
  • Vicky Kumar,
  • Siti Nooriza Abd Razak,
  • Adamu Abubakar Sani,
  • Priyanka Singh

摘要

Incorporating oily sludge ash (OSA) into fly-ash based geopolymers addresses environmental disposal issues and enhances sustainability. Geopolymer mortars were synthesized to identify the optimal alkali activator ratio. Thereafter, OSA content (0–10%) were incorporated to explore the effects on some technical properties of the mortar. Compressive and flexural strengths were measured at 7, 14, and 28 days, and durability was assessed via water absorption; microstructural properties were analysed by X-ray Fluorescence (XRF), Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDX) and Fourier Transform Infrared Spectroscopy (FTIR). The geopolymer with 35% NaOH and 65% Na₂SiO3 had the optimal alkali activator ratio as evident by the compressive and flexural strengths of 30.98 MPa and 5.90 MPa, respectively. Incorporating 2.5% OSA into this mix further improved densification and strength, but higher replacements (5 − 10%) reduced strength due to excess unreacted carbon and alkali imbalance. XRF indicated OSA contains high CaO (33.9%) and Fe₂O₃ (25.4%), complementing the SiO₂ (47.2%) and Al₂O₃ (17.4%) of fly ash. SEM-EDS of the optimal geopolymer revealed well-dispersed angular OSA particles filling voids and major binder elements (Oxygen:42%, Carbon:34% and Silicon: 9%), confirming aluminosilicate gel formation. FTIR spectra exhibited a dominant Si–O–Si/Al band (1009 cm⁻¹) and no characteristic petroleum-hydrocarbon peaks. Cradle-to-site life cycle analysis showed that fly ash and OSA contribute < 1% to the composite’s embodied carbon, yielding a very low carbon footprint. Peak eco-strength efficiency of 0.107 MPa/ (kg CO₂/kg)) was obtained at 2.5% OSA, demonstrating that moderate OSA additions improve structural performance relative to emissions.