Characterization, Activation and Reactivity of Natural Pozzolans for Use as Supplementary Cementitious Materials

Licentiatavhandling, 2024

Supplementary cementitious materials (SCMs) represent one of the most practicable ways to reduce the negative environmental impact of cement. Natural pozzolans like clays and volcanic materials (VMs) offer promising alternatives to industrial by-products such as blast furnace slags and fly ashes, whose availability cannot meet the growing demand for SCMs globally. However, comprehensive implementation of these pozzolans in the built sector, raises unanswered questions. One key concern is understanding the activation requirements of pozzolans with diverse compositions, which can impact their physicochemical properties and reactivity. In this context, the present thesis investigates how commonly used activation methods affect particle size, surface areas, and chemical properties, influencing the reactivity of multiple samples of heterogeneous clays and volcanic materials from the Nordic region, differing in mineralogical characteristics. In the context of heterogeneous natural clays, it is frequently noted that either traditional thermal activation (TA) or mechanochemical activation (MCA) can fully dehydroxylate minerals, a process crucial for optimal clay reactivity. However, findings from the current investigations highlight that combining these methods brings notable changes in key parameters. Notably, integrating 20 mins of MCA at 500 rpm with prior thermal treatment at 800°C led to 158% increase in specific surface area compared to MCA on un-calcined clays. This was associated with a 127% improvement in reactivity levels, when compared to the levels possible from traditional activations. Regarding volcanic materials (VMs), prolonged MCA durations of up to 20 mins demonstrate significant modifications in physical and chemical parameters. Compared to 5 mins of MCA at 500 rpm, 20 mins of MCA resulted in a notable reduction of up to 76% in D50, a substantial increase of up to 225% in surface area, and a rise of up to 47% in amorphous content, accompanied by observable increases in reactivity levels.