When Feedstock Changes, So Does Performance: Feedstock variability, QA/QC, and the hidden cost of compositional drift.*

Industrial by-products are not static materials.

They evolve.

In recent work, a peer-reviewed study published in Materials Today Communications by Skane & Gildenhuys et al. investigated how Western Australian fly ash sourced from the same region changed composition over a 15-year period. The study examined how these changes altered geopolymer performance.

The findings from the research, titled Compositional shifts in fly ash over a decade and its effect on geopolymer properties, have important implications for quality control, standardisation, and commercial deployment. These findings can be extrapolated for considerations when using any by-product material.

The Hidden Variable: Compositional Drift

Fly ash from Collie (WA) collected in 2023 was compared to material sourced from the same region in 2007–2009. Despite originating from the same geographic area, significant differences were observed:

• Mullite content increased from approximately 13.7 wt% to 21.2 wt%

• Amorphous fraction decreased from approximately 64 wt% to 52 wt%

• Amorphous Si/Al ratio shifted from approximately 1.7 to 2.5

• Mullite stoichiometry shifted (x ≈ 0.32 → 0.273)

  
  

These changes are attributed to evolving coal seam sourcing and altered furnace conditions during power generation. The key takeaways are as follows:

Even intra-source feedstocks can drift significantly over time; and

You cannot assume reproducibility across time, even from the same supplier.

Processed fly ash XRF data from Western Australia between 2019 to the present study (last Muja data point) as blue circle and orange cross markers, respectively. Long and short dashed trends are provided only as visual guides to indicate general scatter in bulk molar Si/Al ratios and are not statistically significant (R2 ≤ 0.10).

Why This Matters for Industry

If compositional drift is not accounted for, several issues may arise:

• Activator dosage may be increased unnecessarily

• Longer or heated curing may be applied to compensate

• Additional milling or blending may need to be introduced, which can skyrocket costs

• Embodied carbon and cost per MPa increases

  
  

In other words, poor feedstock control increases both cost and carbon emissions.

The QA/QC Imperative

This study reinforces the importance of:

• Ongoing material characterisation methods, such as fully quantitative XRD phase analysis

• Routine intra-source monitoring

• Database-driven mix redesigning

  
  

Feedstock characterisation is not a one-off exercise. It must be continuous. As coal-fired generation declines and sourcing patterns shift, variability may increase rather than decrease.

Scanning Electron Microscopy (SEM) of Western Australian fly ash at the micrometer scale. Reformix (c).

The Broader Implication

Geopolymer systems are often described as sensitive to activator chemistry and curing regimes. This work demonstrates that precursor drift alone can fundamentally alter binder and strength behaviour.

Standardisation begins at the feedstock.

Conclusion

In conclusion, the evolution of industrial by-products such as fly ash is a critical factor that must be considered in the development of sustainable materials. The research highlights the necessity for continuous monitoring and adaptation in material sourcing and processing. By understanding the implications of compositional drift, industries can better control costs and reduce carbon emissions.

As we move towards a more sustainable future, it is imperative to embrace the principles of the circular economy. Reformix aims to revolutionize industries by transforming industrial by-products into sustainable, high-performance commercial materials. We seek to lead the way in circular economy solutions, helping partners reduce waste and CO2 emissions while building a more eco-friendly future.

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Citation: R. Skane, H. Gildenhuys, A. van Riessen, E. Jamieson, J. Allery, X. Sun, and W. D. Rickard, “Compositional shifts in fly ash over a decade and its effect on geopolymer properties,” Materials Today Communications, vol. 50, p. 114567, 2026.