Natural Low-Kaolinite Clays and Volcanic Materials as SCMs: Activation, Hydration Pathways and Porosity Evolution

Doktorsavhandling, 2026

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.