FA
F. Aghabeyk
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1
Mechanisms of long-term drying shrinkage in blended alkali-activated materials
The synergistic role of curing, microstructure, and gel chemistry
The shrinkage behavior of alkali-activated materials (AAMs) is governed by the combined effects of precursor type, activator chemistry, and curing conditions, which control microstructure development and hydration gel formation. The synergistic interaction between these two factors ultimately dictates the material’s shrinkage behavior. Due to the varying reaction kinetics of raw materials, short-term shrinkage measurements often fail to capture the long-term effects of these influencing factors on the material’s dimensional stability. In this work, slag/fly ash-based AAM with varying alkali contents were cast and subjected to different durations of sealed curing before long-term drying shrinkage tests (up to one year). Pore structure and gel chemistry were analyzed to decouple their roles in shrinkage behavior. Results show that prolonged initial curing drastically reduces shrinkage, while early exposure to drying accelerates shrinkage kinetics. When exposed to drying at an early age, mixes with higher fly ash content exhibited the greatest shrinkage after one year, whereas if cured for a longer duration, mixes with higher slag content exhibited the highest shrinkage strain. Shrinkage–mass loss relationships followed a three-stage S-curve, reflecting the combined effects of pore structure and gel characteristics. By isolating specimens with comparable pore structures at the time of exposure, gel characteristics were shown to directly govern shrinkage, with higher Na/Si ratios disrupting the C-(N)-A-S-H gel network and increasing shrinkage. Thus, this work bridges microstructural insights with practical mix design, enabling the development of AAM binders with reduced shrinkage and improved durability.
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The shrinkage behavior of alkali-activated materials (AAMs) is governed by the combined effects of precursor type, activator chemistry, and curing conditions, which control microstructure development and hydration gel formation. The synergistic interaction between these two factors ultimately dictates the material’s shrinkage behavior. Due to the varying reaction kinetics of raw materials, short-term shrinkage measurements often fail to capture the long-term effects of these influencing factors on the material’s dimensional stability. In this work, slag/fly ash-based AAM with varying alkali contents were cast and subjected to different durations of sealed curing before long-term drying shrinkage tests (up to one year). Pore structure and gel chemistry were analyzed to decouple their roles in shrinkage behavior. Results show that prolonged initial curing drastically reduces shrinkage, while early exposure to drying accelerates shrinkage kinetics. When exposed to drying at an early age, mixes with higher fly ash content exhibited the greatest shrinkage after one year, whereas if cured for a longer duration, mixes with higher slag content exhibited the highest shrinkage strain. Shrinkage–mass loss relationships followed a three-stage S-curve, reflecting the combined effects of pore structure and gel characteristics. By isolating specimens with comparable pore structures at the time of exposure, gel characteristics were shown to directly govern shrinkage, with higher Na/Si ratios disrupting the C-(N)-A-S-H gel network and increasing shrinkage. Thus, this work bridges microstructural insights with practical mix design, enabling the development of AAM binders with reduced shrinkage and improved durability.
The growing incineration of municipal solid waste results in hazardous byproducts, particularly municipal solid waste incineration (MSWI) fly ash and air pollution control (APC) residues. The high toxicity of these residues limits their potential for recycling, leading to their direct disposal in landfills. This landfilling poses a significant environmental risk and presents a major challenge in countries with limited availability of land, such as the Netherlands. In this study, the physicochemical properties of Dutch MSWI fly ash and APC residues were evaluated, including, for the first time, an assessment of trace metal concentrations. High concentrations of heavy metals such as Zn, Pb, Cu, and Cd were identified in most MSWI fly ash and APC residues, along with notable concentrations of trace metals like Bi, suggesting new opportunities for resource recovery. The most hazardous residues were characterized by high contents of chloride, sulfate, alkali oxides, or carbonates, along with low calcium content in their chemical composition. These findings provide valuable insights for the targeted treatment and potential recycling of hazardous MSWI fly ash and APC residues currently being landfilled in the Netherlands.
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The growing incineration of municipal solid waste results in hazardous byproducts, particularly municipal solid waste incineration (MSWI) fly ash and air pollution control (APC) residues. The high toxicity of these residues limits their potential for recycling, leading to their direct disposal in landfills. This landfilling poses a significant environmental risk and presents a major challenge in countries with limited availability of land, such as the Netherlands. In this study, the physicochemical properties of Dutch MSWI fly ash and APC residues were evaluated, including, for the first time, an assessment of trace metal concentrations. High concentrations of heavy metals such as Zn, Pb, Cu, and Cd were identified in most MSWI fly ash and APC residues, along with notable concentrations of trace metals like Bi, suggesting new opportunities for resource recovery. The most hazardous residues were characterized by high contents of chloride, sulfate, alkali oxides, or carbonates, along with low calcium content in their chemical composition. These findings provide valuable insights for the targeted treatment and potential recycling of hazardous MSWI fly ash and APC residues currently being landfilled in the Netherlands.
Journal article
(2025)
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Mayank Gupta, Seyed Hasan Hajiabadi, Farnaz Aghabeyk, Yun Chen, Reinier van Noort, Mahmoud Khalifeh, Guang Ye
While ensuring the long-term integrity of wellbore sealants is critical for the success of geological carbon storage (GCS), the chemical degradation of conventional materials under CO₂-rich conditions remains a major challenge. This study investigates the carbonation behavior of a one-part granite-based geopolymer, integrating a novel pore-scale simulation framework with experimental validation. A new model, ReacSan, is developed to simulate CO₂ transport and carbonation reactions within the evolving microstructure of the geopolymer under GCS-relevant conditions. The framework incorporates CO₂ dissolution using the Redlich–Kwong equation of state, gel dissolution via transition state theory, ion transport using the Lattice Boltzmann Method, and chemical reactions through thermodynamic modeling. The model was validated through experiments exposing equivalent geopolymer samples to CO₂ under in-situ conditions. The experimentally observed rapid carbonation, leading to a decrease in pore fluid pH and the precipitation of CaCO₃ matched the numerical simulations well, demonstrating the ability of the novel ReacSan framework to capture both temporal and spatial variations in the microstructure and carbonation mechanisms of alkali-activated materials (AAMs) exposed to supercritical CO₂. Based on the demonstrated validity of the model, the model is capable of providing detailed predictions of carbonation progression of AAMs or any other sealants over longer time- and length-scales required to ensure long-term GCS integrity.
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While ensuring the long-term integrity of wellbore sealants is critical for the success of geological carbon storage (GCS), the chemical degradation of conventional materials under CO₂-rich conditions remains a major challenge. This study investigates the carbonation behavior of a one-part granite-based geopolymer, integrating a novel pore-scale simulation framework with experimental validation. A new model, ReacSan, is developed to simulate CO₂ transport and carbonation reactions within the evolving microstructure of the geopolymer under GCS-relevant conditions. The framework incorporates CO₂ dissolution using the Redlich–Kwong equation of state, gel dissolution via transition state theory, ion transport using the Lattice Boltzmann Method, and chemical reactions through thermodynamic modeling. The model was validated through experiments exposing equivalent geopolymer samples to CO₂ under in-situ conditions. The experimentally observed rapid carbonation, leading to a decrease in pore fluid pH and the precipitation of CaCO₃ matched the numerical simulations well, demonstrating the ability of the novel ReacSan framework to capture both temporal and spatial variations in the microstructure and carbonation mechanisms of alkali-activated materials (AAMs) exposed to supercritical CO₂. Based on the demonstrated validity of the model, the model is capable of providing detailed predictions of carbonation progression of AAMs or any other sealants over longer time- and length-scales required to ensure long-term GCS integrity.
Review
(2024)
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Boyu Chen, Priyadharshini Perumal, Farnaz Aghabeyk, Adeolu Adediran, Mirja Illikainen, Guang Ye
The pursuit of low-carbon binders as alternatives to Portland cement has sparked interest in developing alkali-activated materials (AAM).1 Using municipal solid waste incineration (MSWI) bottom ash as precursor for AAM has attracted increasing attention as it offers a sustainable, resource-efficient solution to mitigate the environmental impacts associated with the landfill of MSWI bottom ash. However, the varying properties of MSWI bottom ash present challenges in its wide application as AAM precursor. This review provides a comprehensive overview of advances in MSWI bottom ash-based AAM,2 with a particular focus on the relationship between the physicochemical properties of MSWI bottom ash and the engineering properties of MSWI bottom ash-based AAM. This work consolidates the most up-to-date understanding of the reaction mechanism and reaction products of MSWI bottom ash, along with the existing knowledge about mix design and microstructure formation of MSWI bottom ash-based AAM. The factors influencing the engineering properties of MSWI bottom ash-based AAM are detailed, and the environmental impacts of MSWI bottom ash-based AAM are reviewed. Ultimately, this review provides recommendations for the standardized and effective use of MSWI bottom ash as AAM precursor.
...
The pursuit of low-carbon binders as alternatives to Portland cement has sparked interest in developing alkali-activated materials (AAM).1 Using municipal solid waste incineration (MSWI) bottom ash as precursor for AAM has attracted increasing attention as it offers a sustainable, resource-efficient solution to mitigate the environmental impacts associated with the landfill of MSWI bottom ash. However, the varying properties of MSWI bottom ash present challenges in its wide application as AAM precursor. This review provides a comprehensive overview of advances in MSWI bottom ash-based AAM,2 with a particular focus on the relationship between the physicochemical properties of MSWI bottom ash and the engineering properties of MSWI bottom ash-based AAM. This work consolidates the most up-to-date understanding of the reaction mechanism and reaction products of MSWI bottom ash, along with the existing knowledge about mix design and microstructure formation of MSWI bottom ash-based AAM. The factors influencing the engineering properties of MSWI bottom ash-based AAM are detailed, and the environmental impacts of MSWI bottom ash-based AAM are reviewed. Ultimately, this review provides recommendations for the standardized and effective use of MSWI bottom ash as AAM precursor.