Étude de l'impact de la biomasse sur les matériaux cimentaires en assainissement par analyses micro-Raman

Biogenic sulfuric acid (BSA) deterioration poses a critical threat to sewer infrastructure, as the microbial oxidation of hydrogen sulfide (H2S) produces sulfuric acid, which aggressively attacks cementitious matrices and leads to the precipitation of expansive sulfate minerals such as gypsum and ettringite. This thesis investigates the degradation mechanisms of various cementitious materials under both mild and severe H2S exposure conditions.Using a multi-scale analytical approach, the work established correlations between macroscopic indicators (mass loss, surface pH drop, dimensional variations) and microstructural and mineralogical transformations. A novel aspect of this study is the application of high-resolution micro-Raman spectroscopic mapping combined with multivariate analysis (PCA, MCR-ALS), alongside SEM-EDS, to spatially resolve biodegradation fronts.The first part reviews chemical and microbiological deterioration mechanisms, exposure conditions (e.g., H2S levels, humidity, biofilms), mitigation strategies (e.g., acid-resistant binders), and Raman spectroscopy applications in cement chemistry.Long-term field studies (~4 years), focusing on selected binder formulations exposed to low (~1-2 ppm) and high (~14 ppm) H2S levels, revealed that even moderate exposure can induce significant mineralogical transformations in the absence of visible degradation. Under severe conditions, extensive gypsum and ettringite formation, along with various calcium carbonate (CaCO3) polymorphs, were identified in all the studied formulations. In addition, secondary phases such as aluminum hydroxide (Al(OH)3), specific to CAC matrices, were also observed. CAC consistently outperformed Portland-based cements by showing thinner degradation fronts and better matrix retention.An accelerated in vivo test was developed, exposing specimens to ~250 ppm H2S in a controlled bioreactor. This test reproduced field-like degradation within 180 days and confirmed the influence of binder chemistry on degradation kinetics. micro-Raman mapping detected early phase changes, confirming the test's predictive value.Overall, this thesis provides new insights into Biogenic sulfuric acid-induced degradation, highlighting the critical role of cement composition. The integration of micro-Raman imaging with chemometric tools enabled a detailed mineralogical characterization with enhanced spatial insight. These findings offer both scientific advances and practical tools for designing more durable sewer infrastructure