PhD in materials sciences (M/F) – Optimization of Cementitious Materials through Mechano-Activation of Clays: Study of Microstructural Modifications

Population and urban growth are driving increasing concrete consumption in the construction sector, resulting in significant cement production responsible for 7% of global CO₂ emissions (Czigler et al., 2020). A global plan for the concrete and cement sector has led to the definition of a roadmap toward carbon neutrality by 2050 (GCCA, 2026). Decarbonization is a major challenge for the cement industry, with the objective of reducing greenhouse gas (GHG) emissions by 90% by 2050, corresponding to a reduction of 10.6 MtCO₂e. According to a report by the United Nations Environment Programme (Scrivener et al., 2016), partial substitution of clinker in cement is the most promising short-term approach, particularly through two technologies: low-CO₂ supplementary cementitious materials and limestone fillers. While some supplementary materials have been well known and used for several decades, their availability is insufficient, and the use of new alternative materials must now be considered and adopted.

Currently, calcined clay and limestone cements are an emerging technology that is gradually being implemented worldwide, although several challenges remain. In practice, calcined clay cements rely on a specific type of highly reactive clay (kaolinite) and on a calcination method (flash calcination). However, this technology is much less effective for other clay types (smectite and illite), which are far more abundant globally. Moreover, from an environmental standpoint, calcination remains energy-intensive and generates associated emissions.
As an alternative solution, mechanical activation by grinding appears to be a promising technology for effectively activating clays with low kaolinite content, although the scientific basis still needs clarification. Mechano-activation induces structural disorder, the formation of crystalline defects, and partial amorphization, which may enhance pozzolanic reactivity. However, the relationships between the applied mechanical energy, the multi-scale structural modifications of clays, their dissolution kinetics, and, more broadly, the final cementitious performance remain to be elucidated.

The objective of this PhD work is to define the optimal conditions for the mechano-activation of TOT-type clays (smectites, illites, etc.) in order to optimize their reactivity in blended cements. During the study, and drawing on the expertise of both research teams, the PhD candidate will combine: monitoring of structural transformations in clays during mechano-activation (using calorimetry, X-ray diffraction (XRD) with Rietveld analysis, solid-state NMR (²⁹Si, ²⁷Al, ¹H), thermal analysis, and infrared spectroscopy); monitoring of the evolution of physical properties (specific surface area, particle size distribution, and interfacial particle properties); assessment of their reactivity in cement pore solution; and evaluation of the rheological and mechanical behavior of cementitious materials incorporating these additives.

This PhD project combines a fundamental understanding of the effects of this activation method on the atomic structure of clays, the study of their reactivity in alkaline environments, and the evaluation of their impact on the mechanical and transport properties of cementitious matrices.