Hydrogen Sulfide Induced Degradation of Mortars and Cement Paste: A Multi-Scale Investigation

Abstract

Cementitious materials used in sewer networks face aggressive biogenic environments that significantly reduce their service life. This study presents a multi-scale evaluation of cementitious materials exposed to biogenic sulfuric acid attack using an accelerated test that simulates sewer-like conditions. Three cement types, CEM I, CEM V/A, and CAC, were tested in both mortar and cement paste forms. Specimens (2x2x2 cm3) were exposed to an H2S-enriched microbial environment for 180 days with microorganisms. Degradation was assessed through macroscopic monitoring (pH, weight, dimensions), SEM-EDS, and micro-Raman spectroscopy coupled with chemometric analysis. CEM I exhibited structural disaggregation and complete mineralogical transformation by day 180. CEM V showed delayed deterioration, preserving its core phases, while CAC demonstrated outstanding durability, with negligible sulfur ingress and stable phase composition. Across all binders, a consistent degradation zonation was observed, comprising sulfur-rich outer layers, chemically altered transition zones, and intact cores. Mortars consistently showed more severe deterioration than pastes, highlighting the role of porosity and microstructural heterogeneity. Micro-Raman spectroscopy, supported by PCA and MCR-ALS, provided detailed spatial insights into sulfate-related phase formation and biodeterioration fronts. Additional tests conducted on larger specimens (4x4x4 cm3) confirmed the reproducibility and scalability of the degradation mechanisms and zonation patterns. Notably, the degradation depths and phase changes matched those seen after 49-month in situ exposure, supporting the test’s predictive power. These results highlight the importance of binder composition and microstructural features in long-term durability and validate the accelerated test as an efficient and representative tool for material selection in aggressive sewer environments.

Keywords: Sewerage Network, Accelerated Biodeterioration, H2S, High-Resolution Microanalysis, chemometrics