Laboratory Test to Evaluate the Resistance of Cementitious Materials to Biodeterioration in Sewer Network Conditions

Abstract

The biodeterioration of cementitious materials in sewer networks has become a major economic, ecological, and public health issue. Establishing a suitable standardized test is essential if sustainable construction materials are to be developed and qualified for sewerage environments. Since purely chemical tests are proven to not be representative of the actual deterioration phenomena in real sewer conditions, a biological test–named the Biogenic Acid Concrete (BAC) test–was developed at the University of Toulouse to reproduce the biological reactions involved in the process of concrete biodeterioration in sewers. The test consists in trickling a solution containing a safe reduced sulfur source onto the surface of cementitious substrates previously covered with a high diversity microbial consortium. In these conditions, a sulfur-oxidizing metabolism naturally develops in the biofilm and leads to the production of biogenic sulfuric acid on the surface of the material. The representativeness of the test in terms of deterioration mechanisms has been validated in previous studies. A wide range of cementitious materials have been exposed to the biodeterioration test during half a decade. On the basis of this large database and the expertise gained, the purpose of this paper is (i) to propose a simple and robust performance criterion for the test (standardized leached calcium as a function of sulfate produced by the biofilm), and (ii) to demonstrate the repeatability, reproducibility, and discriminability of the test method. In only a 3-month period, the test was able to highlight the differences in the performances of common cement-based materials (CEM I, CEM III, and CEM V) and special calcium aluminate cement (CAC) binders with different nature of aggregates (natural silica and synthetic calcium aluminate). The proposed performance indicator (relative standardized leached calcium) allowed the materials to be classified according to their resistance to biogenic acid attack in sewer conditions. The repeatability of the test was confirmed using three different specimens of the same material within the same experiment and the reproducibility of the results was demonstrated by standardizing the results using a reference material from 5 different test campaigns. Furthermore, developing post-testing processing and calculation methods constituted a first step toward a standardized test protocol.

In situ concrete sewer performance: comparison of Portland cement, calcium sulfoaluminate cement, and calcium aluminate cement

“…7(B) shows continuous microcracking parallel to the exposed surface, yet not fully demarcating the deteriorated zone from the transition zone. , ettringite formation, due to CSA hydration and sulphate penetration, as pointed out by Aboulela [39]. CSA concrete microstructure also has a high concentration of aggregate phases, followed by ettringite, Ca-aluminate, gibbsite, Portlandite, and gypsum.…”

“…7 SEM-BSE image for CSA concrete after two years of exposure at NAS: B is the zoomed section in A QEMSCAN analysis of CSA concrete (Fig 8) also does not clearly demarcate the deteriorated and transition zones. This is possibly associated with the superposition of ettringite in the transition zone, i.e., ettringite formation, due to CSA hydration and sulphate penetration, as pointed out by Aboulela[39]. CSA concrete microstructure also has a high concentration of aggregate phases, followed by ettringite, Ca-aluminate, gibbsite, Portlandite, and gypsum.…”

“…At NAS, CEM II had pHs between 5 and 4.5, and CSA and CAC had around 4. At this stage, CAC had the lowest pH, possibly linked to decreased calcium ion leaching [32] and gibbsite production, which is stable at pH 3-4. LPS concrete, in contrast, had surface pHs between 5.5 and 5.0 higher than NAS concrete because of corrosion deposit removal due to sewer hydraulic actions [33] This implies that concrete surface pH does not necessarily reflect sewer aggressivity but rather the interaction between concrete alkaline reactive components and acid production.…”

“…Under XRD analysis, gibbsite was not readily observed in the deteriorated zone, although significantly mapped under QEMSCAN analysis. According to Aboulela [39], only amorphous gibbsite is formed in the deteriorated zone of CSA concrete, which could not be detected under XRD analysis. This is because amorphous phases produce wide X-ray scattering profiles, which are difficult to detect in XRD patterns with high peaks of crystalline phases [46].…”