Natural Low-Kaolinite Clays and Volcanic Materials as SCMs: Activation, Hydration Pathways and Porosity Evolution
Doctoral thesis, 2026
This thesis investigates the viability of naturally heterogeneous low-kaolinite clays and volcanic materials as supplementary cementitious materials (SCMs) for low-carbon binders. The work is motivated by the need to reduce clinker content in cement under climate constraints and in view of the declining availability of conventional SCMs such as fly ash and slag. In contrast to the kaolinite-rich clays that dominate much of the literature, the materials studied here are mineralogically complex and more representative of abundant natural aluminosilicate resources. The thesis therefore examines how activation modifies their structure and reactivity, and how these changes govern hydration, aluminium partitioning, strength development, and pore structure evolution in blended cement systems.
The results show that the two pozzolan groups respond differently to activation routes. For the clays, a combined thermo-mechanochemical activation (TA-MCA) was effective in improving pozzolanic reactivity. Compared to conventional thermal activation (TA), the TA-MCA improved reactivity by up to 353% and by 127% relative to mechanochemical activation alone (MCA). This was accompanied by increases in amorphization of up to 124%, specific surface areas increases up to 374%, and pronounced atomic-scale Al-Si network disruption. TA–MCA produced the greatest structural disruption, together with high atomic-scale Al–Si network disruption. TA-MCA caused reduction of crystalline Al(VI) by 88% compared with TA and by 94% compared with MCA and the strongest broadening of 27Al/29Si resonances. For the volcanic materials, MCA improved reactivity across mineralogically diverse precursors, increasing MR3 reactivity from about 40-60 to 400 J/g SCM. In blended cements, the activated clays produced dense microstructures and strong later-age performance, with binary blends at 20-40 wt.% replacement reaching up to 125% of ordinary Portland cement (OPC) strength at 56 days and the 30 wt.% blend showing a 42% reduction in total porosity. Aluminium was found to be incorporated preferentially into C-(A)-S-H rather than predominantly into AFm phases, which promoted pore refinement but limited limestone synergy. The volcanic blends hydrated through a more distributed assemblage involving C-(A)-S-H, AFt, possibly strätlingite, and Mg-Al layered double hydroxide-type phases. Although their strength development was slower, 30 wt.% replacement reached OPC-comparable strength at 56 days, while 40 wt.% replacement still achieved about 92% of OPC strength. Overall, the thesis highlights the potential of complex heterogeneous natural pozzolans to be viable SCMs if mechanisms of their activation and hydration are adequately understood.
The results show that the two pozzolan groups respond differently to activation routes. For the clays, a combined thermo-mechanochemical activation (TA-MCA) was effective in improving pozzolanic reactivity. Compared to conventional thermal activation (TA), the TA-MCA improved reactivity by up to 353% and by 127% relative to mechanochemical activation alone (MCA). This was accompanied by increases in amorphization of up to 124%, specific surface areas increases up to 374%, and pronounced atomic-scale Al-Si network disruption. TA–MCA produced the greatest structural disruption, together with high atomic-scale Al–Si network disruption. TA-MCA caused reduction of crystalline Al(VI) by 88% compared with TA and by 94% compared with MCA and the strongest broadening of 27Al/29Si resonances. For the volcanic materials, MCA improved reactivity across mineralogically diverse precursors, increasing MR3 reactivity from about 40-60 to 400 J/g SCM. In blended cements, the activated clays produced dense microstructures and strong later-age performance, with binary blends at 20-40 wt.% replacement reaching up to 125% of ordinary Portland cement (OPC) strength at 56 days and the 30 wt.% blend showing a 42% reduction in total porosity. Aluminium was found to be incorporated preferentially into C-(A)-S-H rather than predominantly into AFm phases, which promoted pore refinement but limited limestone synergy. The volcanic blends hydrated through a more distributed assemblage involving C-(A)-S-H, AFt, possibly strätlingite, and Mg-Al layered double hydroxide-type phases. Although their strength development was slower, 30 wt.% replacement reached OPC-comparable strength at 56 days, while 40 wt.% replacement still achieved about 92% of OPC strength. Overall, the thesis highlights the potential of complex heterogeneous natural pozzolans to be viable SCMs if mechanisms of their activation and hydration are adequately understood.
Supplementary cementitious materials
thermo-mechanochemical activation
volcanic materials
low-kaolinite clays
low-carbon binders.
hydration
aluminium partitioning
pozzolanic reactivity
pore structure
SB-Hall 6 Samhällsbyggnnad 1, Sven Hultings gata 6, Chalmers University of Technology, Göteborg
Opponent: Iveta Novakova, Associate Professor, The Arctic University of Norway, Norway
Author
Amrita Hazarika
Chalmers, Architecture and Civil Engineering, Structural Engineering
Characterisation, activation, and reactivity of heterogenous natural clays
Materials and Structures/Materiaux et Constructions,;Vol. 57(2024)
Journal article
Characterization, activation and reactivity – A case study of Nordic volcanic materials for application as Supplementary Cementitious Materials
Case Studies in Construction Materials,;Vol. 22(2025)
Journal article
Evolution of hydration in cement blends with incorporation of activated low-kaolinite clays: Insights into the preferred aluminum uptake by C-(A)-S-H
Cement and Concrete Research,;Vol. 201(2026)
Journal article
Amrita Hazarika, Hegoi Manzano, Juan Gaitero Redondo, Eduardo Duque Redondo, Liming Huang, Joao Figueira, and Arezou Babaahmadi. “Insights into the atomic-scale structural disorder in low-kaolinite heterogenous natural clays under combined thermo-mechanochemical activation.”
Amrita Hazarika, Johan Dalene, Klaartje de Weerdt, Ingemar Löfgren, Liming Huang, Joao Figueira, and Arezou Babaahmadi. “Hydration, Phase Assemblage, and Elemental Partitioning in Cement Blends with Activated Volcanic Materials as SCMs.”
Natural Low-Kaolinite Clays and Volcanic Materials as SCMs for Cleaner Cement
Like flour in a cake, at the heart of concrete is cement which is the key binding ingredient that turns loose particles into a rock-like material. It is produced in billions of tonnes every year and makes possible the homes, bridges, railways, water systems, and energy infrastructure on which modern life depends. At the same time, cement production generates very high carbon emissions, making the cement industry the world’s third-largest CO2 emitting sector. Demand for cement-based construction is only expected to grow as the world sees increasing infrastructure-led stimulus projects across many regions. This thesis begins from a central tension: concrete is indispensable for continued infrastructural and human progress, yet the cement that makes it possible must become far less carbon-intensive.
One of the most practical ways to reduce cement’s climate impact is to replace part of it with other reactive mineral materials. But the conventional substitutes long used by industry, such as fly ash and slag, are becoming less available. This thesis therefore explores a different path by studying abundantly available natural materials, specifically low-kaolinite clays and volcanic materials as realistic alternatives for lower-carbon construction.
A central idea in the work is that nature does not usually provide “perfect” raw materials. Much of the scientific literature focuses on ideal, highly reactive clays, but real deposits are often far more mixed and complex. Instead of studying only the easiest materials, this thesis focuses on mineralogically heterogeneous clays and volcanic materials that better represent what is actually abundant in the world. It examines how these materials can be “activated” by using heat, grinding, or a combination of both, so that they become reactive enough to participate in cement chemistry. It then follows the consequences across scales, from changes in atomic structure to their effects on hydration, strength, and the tiny pore networks that influence how strong and durable a binder becomes.
The thesis shows that through activation, these natural materials can be made significantly more useful for low-carbon cement, but that each group of pozzolan requires a different treatment. The natural clays performed best when activated through a combination of heat and intensive grinding regime proposed in this thesis, while the volcanic materials responded strongly to grinding alone. Once treated, both were able to replace part of ordinary cement while still producing strong, dense binders over time. The work also explains the chemistry behind this behaviour. In the clay-based systems, aluminium dominantly entered the main binding phase of the cement known as C-(A)-S-H, that contributes to strength. In the volcanic systems, elements such as reactive magnesium and iron can influence how the materials reacted and hardened. Overall, the thesis shows that abundant natural resources can be transformed into practical ingredients for cleaner cement and more sustainable construction.
Like flour in a cake, at the heart of concrete is cement which is the key binding ingredient that turns loose particles into a rock-like material. It is produced in billions of tonnes every year and makes possible the homes, bridges, railways, water systems, and energy infrastructure on which modern life depends. At the same time, cement production generates very high carbon emissions, making the cement industry the world’s third-largest CO2 emitting sector. Demand for cement-based construction is only expected to grow as the world sees increasing infrastructure-led stimulus projects across many regions. This thesis begins from a central tension: concrete is indispensable for continued infrastructural and human progress, yet the cement that makes it possible must become far less carbon-intensive.
One of the most practical ways to reduce cement’s climate impact is to replace part of it with other reactive mineral materials. But the conventional substitutes long used by industry, such as fly ash and slag, are becoming less available. This thesis therefore explores a different path by studying abundantly available natural materials, specifically low-kaolinite clays and volcanic materials as realistic alternatives for lower-carbon construction.
A central idea in the work is that nature does not usually provide “perfect” raw materials. Much of the scientific literature focuses on ideal, highly reactive clays, but real deposits are often far more mixed and complex. Instead of studying only the easiest materials, this thesis focuses on mineralogically heterogeneous clays and volcanic materials that better represent what is actually abundant in the world. It examines how these materials can be “activated” by using heat, grinding, or a combination of both, so that they become reactive enough to participate in cement chemistry. It then follows the consequences across scales, from changes in atomic structure to their effects on hydration, strength, and the tiny pore networks that influence how strong and durable a binder becomes.
The thesis shows that through activation, these natural materials can be made significantly more useful for low-carbon cement, but that each group of pozzolan requires a different treatment. The natural clays performed best when activated through a combination of heat and intensive grinding regime proposed in this thesis, while the volcanic materials responded strongly to grinding alone. Once treated, both were able to replace part of ordinary cement while still producing strong, dense binders over time. The work also explains the chemistry behind this behaviour. In the clay-based systems, aluminium dominantly entered the main binding phase of the cement known as C-(A)-S-H, that contributes to strength. In the volcanic systems, elements such as reactive magnesium and iron can influence how the materials reacted and hardened. Overall, the thesis shows that abundant natural resources can be transformed into practical ingredients for cleaner cement and more sustainable construction.
New era for cement replacement materials: Importance of service life design (NewDurCem)
Formas (2020-01061), 2021-01-01 -- 2024-12-31.
Subject Categories (SSIF 2025)
Other Civil Engineering
Other Materials Engineering
DOI
10.63959/chalmers.dt/5875
ISBN
978-91-8103-418-9
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5875
Publisher
Chalmers
SB-Hall 6 Samhällsbyggnnad 1, Sven Hultings gata 6, Chalmers University of Technology, Göteborg
Opponent: Iveta Novakova, Associate Professor, The Arctic University of Norway, Norway