Investigation of test methods to qualify cementitious materials subjected to biological attack in sewer conditions

Author(s): Amr Aboulela, Matthieu Peyre-Lavigne and Alexandra Bertron
Paper category: Proceedings
Book title: Proceedings of the Final Conference of RILEM 253-MCI Microorganisms-Cementitious Materials Interactions Volume I
Editor(s): Alexandra Bertron and Henk Jonkers
ISBN: 978-2-35158-207-7 (Set)
ISBN: 978-2-35158-209-1 (Volume1)
e-ISBN: 978-2-35158-206-0
Publisher: RILEM Publications SARL
Publication year: 2018
Pages: 45-56
Total Pages: 288
Language : English

Abstract: In sewers, biogenic sulfuric acid is produced from the oxidization of the hydrogen sulfide - present in the air phase - by microorganisms on the concrete surface, leading to the progressive dissolution of cementitious materials and to deleterious secondary precipitations of gypsum and/or ettringite. Standards intended for the assessment of cementitious materials and products in sewer environments recommend chemical tests by immersion in sulfuric acid (H2SO4) solution. However, the comparison of in-situ and chemical laboratory tests’ results showed different performance ranking for cementitious materials. Moreover, the scientific literature widely recognizes that purely chemical tests are not representative of the real phenomenon. Hence, the purpose of this study was to compare chemical and biological tests in terms of kinetics and mechanisms of alteration to evaluate the relevance and the representativeness of different test designs.
Different cementitious binders were subjected to a biological test (BAC-test) and a chemical test (adapted from French Standard NF EN 598), with chemical conditions similar to the biological test. The leaching solutions were monitored during the testing period by pH measurements and quantification of leached calcium, aluminum and sulfate. At the end, the cement samples were analyzed by SEM+EDS and XRD to evaluate the degraded depth and to identify the chemical alteration mechanisms of the cementitious matrix.
Degraded depths were observed and found to be deeper on specimens exposed to biological test. Leached cations were different in terms of kinetics and quantification. Crystallized elemental sulfur was found only on the surface of the specimens exposed to biological deterioration. Generally, the purely chemical test under-estimated the degradation phenomenon and, therefore, the biological aspect must be taken into account to assess cementitious materials intended for sewage networks.

Online publication : 2018
Publication type : full_text
Public price (Euros) : 0.00