review · Cement and Concrete Composites
Volcanic ash offers a promising, lower-energy feedstock for sustainable construction binders, requiring less processing energy than alternatives like fly ash or calcined clay. When activated with alkalis, the material displays low natural reactivity because of limited amorphous content and poor metal solubility at high pH levels, though mechanochemical processing can improve these properties. In contrast, acid phosphate activation delivers higher reactivity and superior engineering properties at ambient temperatures due to better solubility of iron, calcium, and magnesium. While acid-activated variants perform well, constraints around phosphate availability limit their use in large-scale building construction. Consequently, acid-activated formulations are better suited for hazardous waste encapsulation, such as nuclear or heavy metal containment. Meanwhile, alkali-activated ash remains viable for binders, brick stabilisation, and rapid concrete repairs, provided further research addresses durability, life cycle impacts, and economic feasibility.
Traditional cement production is energy-intensive and carbon-heavy. Volcanic ash represents an abundant, non-disruptive natural alternative that demands less energy to prepare. Understanding whether to process it with alkalis or acids helps researchers and manufacturers select the best chemical routes for greener structural building products or specialised containment solutions for toxic and nuclear waste.
This research outlines early-stage to applied pathways for construction material manufacturers, civil contractors, and waste management operators. Potential applications include low-energy binders, brick stabilisation, rapid concrete repair, and hazardous waste encapsulation. However, commercial adoption remains at an early stage, as full deployment requires further investigation into long-term durability, life cycle assessments, techno-economic viability, and the supply constraints associated with phosphate activators.
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This review provides a comprehensive study of the fundamentals of the alkaline and acid activation of volcanic ashes (VA), for mainstreaming their use as a conventional feedstock for developing geopolymers and their applications. The low reactivity in an alkaline environment is driven by the low content of the amorphous phase and the low solubility of iron, calcium and magnesium at pH > 12. Nevertheless, techniques such as mechanochemical activation has significantly improved the reactivity and the properties of the resulting products. In the acid phosphate medium, the high solubility of iron, calcium and magnesium ensures good reactivity and a high reaction rate at room temperature. As a result, the engineering properties of acid-phosphate-activated volcanic ash are superior to those of alkali-activated volcanic ash. The resulting materials have great potential for use as binders in concrete design, for the stabilization of compressed earth bricks and for the rapid repair of deteriorated concrete structures. However, significant research is required to fully understand their durability performances, life cycle and techno-economic viability for large-scale utilisation. Further, the limited availability of phosphate resources makes acid activation not a viable route to activate volcanic ash for building purposes. The acid-activated volcanic ash has potential in waste management applications such as nuclear waste or heavy metal encapsulation. Finally, volcanic ash emerges as a promising raw material for developing sustainable building materials through alkali and acid activation. This holds as its exploitation is non-disruptive, and processing requires less energy compared to calcined clay or fly ash.
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DOI: 10.1016/j.cemconcomp.2024.105660
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