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<p>The cement industry accounts for nearly 8–10% of global CO<sub>2</sub> emissions, driving the need for sustainable alternatives to ordinary Portland cement. This study evaluates the feasibility of fully replacing commercial sodium hydroxide (CA-SH) with recovered caustic solution (RCS), a textile industry waste, as an alkaline activator in geopolymer concrete. The RCS was used in its as-received state (0.81&#xa0;M NaOH-equivalent) and experimentally characterized for alkalinity speciation, electrical conductivity, organic content, and trace metals to ensure consistency and reproducibility. Two geopolymer systems were investigated, namely fly ash-based (F-RCS) and binary fly ash–GGBS-based (GF-RCS) mixes, with RCS substitution levels ranging from 0 to 100%, while 50% natural river sand was replaced with manufactured sand to enhance sustainability. Mechanical performance, water absorption, and thermal stability up to 900&#xa0;°C were evaluated under ambient curing, supported by SEM and normalized Raman spectroscopy.As The results indicate that increasing RCS content reduced compressive strength in F-RCS mixes, with F-RCS100 showing a 27% strength loss due to lower effective hydroxide activity, whereas the binary GF-RCS system exhibited improved performance, with GF-RCS100 achieving 16% higher compressive strength, 14% higher split tensile strength, and 15% higher flexural strength than the control. Raman analysis confirmed enhanced polymerization and greater formation of calcium-enriched C–A–S–H/N–A–S–H hybrid gels, which correlated with improved mechanical properties. This study demonstrates the direct utilization of recovered caustic solution (RCS) generated from textile processing wastes as a sustainable alkaline activator for geopolymer concrete without chemical purification. GF-RCS100 also showed 46% lower water absorption and retained a residual compressive strength of 24.7&#xa0;MPa after high-temperature exposure. Economic and environmental analyses revealed over 50% cost savings and approximately 15% reduction in global warming potential compared with NaOH-activated systems, demonstrating the technical feasibility of RCS as a sustainable alkaline activator for binary geopolymer concrete, while highlighting long-term durability as future research scope.</p> Graphical Abstract <p></p>

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Sustainable Fly Ash-GGBS Geopolymer Concrete Using Industrial Caustic Waste: Raman-Enhanced Microstructural and Performance

  • 期刊论文

  • 发表日期：

    2026年3月19日

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  • Shani Singh,
  • Raman Nateriya,
  • Juned Raheem

摘要

The cement industry accounts for nearly 8–10% of global CO2 emissions, driving the need for sustainable alternatives to ordinary Portland cement. This study evaluates the feasibility of fully replacing commercial sodium hydroxide (CA-SH) with recovered caustic solution (RCS), a textile industry waste, as an alkaline activator in geopolymer concrete. The RCS was used in its as-received state (0.81 M NaOH-equivalent) and experimentally characterized for alkalinity speciation, electrical conductivity, organic content, and trace metals to ensure consistency and reproducibility. Two geopolymer systems were investigated, namely fly ash-based (F-RCS) and binary fly ash–GGBS-based (GF-RCS) mixes, with RCS substitution levels ranging from 0 to 100%, while 50% natural river sand was replaced with manufactured sand to enhance sustainability. Mechanical performance, water absorption, and thermal stability up to 900 °C were evaluated under ambient curing, supported by SEM and normalized Raman spectroscopy.As The results indicate that increasing RCS content reduced compressive strength in F-RCS mixes, with F-RCS100 showing a 27% strength loss due to lower effective hydroxide activity, whereas the binary GF-RCS system exhibited improved performance, with GF-RCS100 achieving 16% higher compressive strength, 14% higher split tensile strength, and 15% higher flexural strength than the control. Raman analysis confirmed enhanced polymerization and greater formation of calcium-enriched C–A–S–H/N–A–S–H hybrid gels, which correlated with improved mechanical properties. This study demonstrates the direct utilization of recovered caustic solution (RCS) generated from textile processing wastes as a sustainable alkaline activator for geopolymer concrete without chemical purification. GF-RCS100 also showed 46% lower water absorption and retained a residual compressive strength of 24.7 MPa after high-temperature exposure. Economic and environmental analyses revealed over 50% cost savings and approximately 15% reduction in global warming potential compared with NaOH-activated systems, demonstrating the technical feasibility of RCS as a sustainable alkaline activator for binary geopolymer concrete, while highlighting long-term durability as future research scope.

Graphical Abstract