Engineering Chemically Stable Geopolymer Activators Through Thermodynamic Modelling*

Peer-Reviewed Research Underpinning Reformix Process Design

Reformix’s approach to geopolymer system design is grounded in materials science, engineering and thermodynamics - not wishful thinking in the laboratory.

'Predicting the stability of geopolymer activator solutions for optimised synthesis through thermodynamic modelling' is a case study written by Skane et. al. and published recently in the esteemed peer-reviewed Chemical Engineering Journal. In this work, the team developed and experimentally validated a dynamic mathematical model to predict the stability of geopolymer activator solutions during preparation. While activators are often treated as simple mixtures of sodium hydroxide and sodium silicate, the dissolution process is highly exothermic and thermochemically dynamic.

Why Activator Stability Matters

Activator preparation directly influences:

"Two activator solutions with identical feedstock compositions, dynamic environmental and mixing conditions, but very different final physicochemical compositions due to different feedstock sequencing. Note that whilst the right activator solution precipitates into a non-stable and highly viscous slurry, the left remains relatively clearer and stabilised with a better flowability, which is better combined with a geopolymer precursor for effective synthesis."

• Reaction kinetics

• Flow behaviour

• Setting profiles

• Strength development

• Industrial scalability

Many laboratory protocols assume extended equilibration periods (e.g. 24 hours). Our experimental calorimetry and modelling demonstrated that:

• NaOH(aq) systems stabilise in under 30 seconds

• NaOH(s) systems stabilise in approximately 1 minute

Despite this, inappropriate mixing or sequencing can induce temperature overshoot, instability and downstream variability.

From Modelling to Industrial Insight

The study integrated:

• Dissolution enthalpy of NaOH

• Heat transfer dynamics and losses

• Activator composition

• Molar ratio (SiO₂/Na₂O) effects

The resulting framework predicts temperature evolution, cooling behaviour and stability windows for activator solutions.

This modelling approach reduces:

• Preparation time

• Safety risk

• Batch variability

• Scaling uncertainty

Most importantly, it provides a reproducible pathway toward activator standardisation; a key requirement for industrial adoption of geopolymer technologies.

"Temperature and differential enthalpy profiles for the experimental activator solution with blue circles and solid black and purple lines representing the experimental measurements and model outputs for the temperature and solution enthalpy, respectively. Red dashed lines are added to clarify the different thermodynamic milestones within the activator solution."

Beyond Academia

While developed within an academic research context, this work directly informs Reformix’s applied engineering methodology. Low-carbon binder systems require control at the solution phase. Strength testing happens days later. Instability begins in minutes.

Understanding the thermodynamics of activator preparation is foundational to reliable geopolymer deployment - and any material you're trying to assess.

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*Citation: R. Skane, P. A. Schneider, F. Jones, A. van Riessen, E. Jamieson, X. Sun and W. D. A. Rickard, “Predicting the Stability of Geopolymer Activator Solutions for Optimised Synthesis through Thermodynamic Modelling,” Chemical Engineering Journal, vol. 515, p. 163543, 2025.