Utilisation d'une souche bactérienne alcalino-résistante productrice de CaCO3 pour l'amélioration de la qualité des granulats de béton recyclé

Microbiologically induced CaCO3 production (MICP) is a process employed in several domains. Biocarbonatation was first study and employ to preserve and repair calcareous ornamental stones. Then, studies have been conducted to use MICP with concrete, with the aim to improve the quality of the material, repair cracks, or produce a self-healing concrete. The aim of this study is to evaluate the interest of using MICP with cement-based road construction. Because recycled concrete aggregate (RCA) are widely used in road construction, this study will focus on the improvement of RCA quality by MICP. So, after the selection of an alkalophilic bacterial strain, there was an analysis and a quantification of its CaCO3 production. Then, X-ray diffraction (XRD) and thermogravimetric analysis (TGA) have been conducted on precipitate formed. After that, selected bacteria have been contacted with RCA to study their influence on RCA's properties.La production de carbonates de calcium par les bactéries est un processus utilisé dans différents domaines. Ce procédé de biocarbonatation a d'abord été étudié et employé pour traiter les pierres ornementales calcaires dans le but de les préserver et de les réparer. Des recherches ont ensuite été menées afin d'utiliser cette capacité des micro-organismes à produire des carbonates de calcium dans le béton. L'objectif est d'améliorer la qualité du béton, réparer les fissures formées ou encore produire un matériau capable d'autoréparation. Une étude pour évaluer l'intérêt de telles bactéries pour les matériaux routiers à base de ciment a débuté. Une des premières pistes envisagées est l'utilisation des bactéries pour améliorer les performances des granulats de béton recyclé pour améliorer leur recyclage dans les matériaux routiers. Après avoir sélectionné une souche bactérienne alcalino-résistante, nous nous sommes intéressés à qualifier et quantifier la production de carbonate de calcium au cours des différentes phases de croissance de la bactérie d'étude. Les précipités formés ont ainsi été analysés par diffraction des rayons X (DRX) et analyses thermogravimétrique (ATG). Dans un second temps, les bactéries ont été mises en contact avec du sable de béton recyclé, et leur effet sur les propriétés d'usage du sable ont été mesurées

Utilisation d’une souche bactérienne alcalino-résistante productrice de CaCO

La production de carbonates de calcium par les bactéries est un processus utilisé dans différents domaines. Ce procédé de biocarbonatation a d’abord été étudié et employé pour traiter les pierres ornementales calcaires dans le but de les préserver et de les réparer. Des recherches ont ensuite été menées afin d’utiliser cette capacité des micro-organismes à produire des carbonates de calcium dans le béton. L’objectif est d’améliorer la qualité du béton, réparer les fissures formées ou encore produire un matériau capable d’autoréparation. Une étude pour évaluer l’intérêt de telles bactéries pour les matériaux routiers à base de ciment a débuté. Une des premières pistes envisagées est l’utilisation des bactéries pour améliorer les performances des granulats de béton recyclé pour améliorer leur recyclage dans les matériaux routiers. Après avoir sélectionné une souche bactérienne alcalino-résistante, nous nous sommes intéressés à qualifier et quantifier la production de carbonate de calcium au cours des différentes phases de croissance de la bactérie d’étude. Les précipités formés ont ainsi été analysés par diffraction des rayons X (DRX) et analyses thermogravimétrique (ATG). Dans un second temps, les bactéries ont été mises en contact avec du sable de béton recyclé, et leur effet sur les propriétés d’usage du sable ont été mesurées

Modelling of the sulfuric acid attack on different types of cementitious materials

A chemical-reactive transport model was used to simulate the sulfuric acid attack of cement pastes based on ordinary Portland cement (CEM I), blended Portland cements (CEM III, CEM IV, and CEM V), and calcium aluminate cement (CAC). This model accounts for the dissolution of cement hydrates (portlandite, C-S-H, hydrogarnet), and the precipitation of deterioration products (ettringite and gypsum). Moreover, diffusion of the aqueous species in the pore space in the material is considered. With this model, we can get the hydrate contents, the porosity, and the deterioration phase contents throughout a sulfuric acid attack. Two indicators are defined to predict the service life of the cementitious materials: the deterioration depth and the dissolved calcium content. These two indicators showed that calcium aluminate cement provide a better resistance to sulfuric acid attack than that of Portland cements. This better resistance is mainly due to the partial dissolution of CAC hydrate as opposed to the total dissolutions of CH and C-S-H

Evaluation of the ability of alkalophilic bacteria to form a biofilm on the surface of Portland cement-based mortars

This paper investigates bacteria colonisation through biofilm formation, based on the premise that biofilm helps bacteria to have a better development. The aim is to homogenize bacterial growth on recycled concrete aggregates (RCA) to obtain a homogeneous precipitation of calcium carbonate (CaCO3). In previous studies, Bacillus halodurans C-125 was selected to perform biocarbonation on RCA to generate a coat of CaCO3 and diminish water absorption. Contrary to expectations, its poor development led to an heterogeneous CaCO3 precipitation, resulting in an inefficient treatment. Within the framework of this criterion the genetic information of B. halodurans C-125 was compared with a homologous specie “Bacillus subtilis str. 168” to know if it possessed the genes to encode Tas A and Tap A proteins. These proteins consolidate a robust biofilm in Bacillus subtilis str. 168, which promotes bacterial development and adhesion to a surface. Remarkably, B. halodurans C-125 lacks the genes to produce Tas A and Tap A. B. halodurans C-125 was also compared with a group of bacteria isolated from RCA to produce biofilm on MSgg media. Curiously, B. halodurans C-125 did not form a robust biofilm while the bacteria isolated from RCA did. Because of the capacity of the isolated bacteria to form biofilm, they were inoculated on a mortar disk with nutrient and MSgg broth. The results showed traces of bacterial development and precipitation of CaCO3 in form of calcite

Abiotic interaction between hydrogen sulphide and cementitious materials

Concrete deterioration is extensively observed due to hydrogen sulphide emission in sewerage networks. The presence of this gas leads to the development of sulphur-oxidizing bacteria which produce sulphuric acid. Local deterioration of concrete sewer pipes, based on dissolution-precipitation mechanisms and the formation of ettringite and gypsum, degrades their mechanical properties and prevents optimum waste water collection. Due to expensive rehabilitation works, innovative sewerage network construction or repair approaches must be established and evaluated. The main final objective of this study is to put forward a representative, quick and standardized test and to develop a predictive model for the service life of different types of concrete in the environment of sewer pipes. This study focuses on interaction between cementitious materials and hydrogen sulphide (H2S) which is the first step of the degradation mechanism. Mortars based on different types of cement (CEM I, CEM IV and CAC) were exposed to H2S under various conditions (relative humidity, pre-exposure to H2S or otherwise). Changes in the H2S concentration were monitored as a function of time and the H2S adsorption rate was calculated. After 6 months of exposure, the state of deterioration of mortars was assessed. Some gypsum crystals on mortar surfaces based on CEM I and CAC cements and a mix of elemental sulphur and gypsum crystals on mortar surfaces based on CEM IV cement were observed by SEM-EDS. The decrease in the H2S adsorption rate, highlighted when the relative humidity decreased and when gypsum was present, must be taken into account in the modelling process.La détérioration du béton dans les réseaux d'assainissement est très souvent obserÎe en raison des émissions de sulfure d'hydrogène. La présence de ce gaz conduit au développement de bactéries oxydant le soufre et produisant de l'acide sulfurique. La détérioration locale des canalisations en béton, basée sur les mécanismes de dissolution-précipitation et la formation de l'ettringite et du gypse, dégrade leurs propriétés mécaniques et empêche la collecte optimale des eaux usées. En raison des travaux de réhabilitation coûteux, il faut établir et évaluer des approches novatrices de construction ou de réparation du réseau d'assainissement. L'objectif final de cette étude est de proposer un test représentatif, rapide et standardisé et de développer un modèle prédictif pour la durée de vie de différents types de béton dans l'environnement des tuyaux d'égout. Cette étude se concentre sur l'interaction entre les matériaux de ciment et le sulfure d'hydrogène (H2S), qui est la première étape du mécanisme de dégradation. Les mortiers à base de différents types de ciment (CEM I, CEM IV et CAC) ont été exposés à H2S dans diverses conditions (humidité relative, pré-exposition à H2S). Les évolutions de la concentration de H2S ont été mesurées en fonction du temps et le taux d'adsorption de H2S a été calculé. Après 6 mois d'exposition, l'état de détérioration des mortiers a été évalué. Des cristaux de gypse sur des surfaces de mortier à base de ciments CEM I et CAC et un mélange de cristaux de soufre et de gypse élémentaires sur des surfaces de mortier à base de CEM IV ont été obserÎs par MEB-EDS. La diminution du taux d'adsorption H2S, mise en évidence lorsque l'humidité relative a diminué et lorsque le gypse était présent, doit être pris en compte dans le processus de modélisation

Aromatic amino acids as precursors of antimicrobial metabolites in Geotrichum candidum

Geotrichum candidum ATCC 204307 was previously found to generate phenyllactic acid (PLA) and indoleacetic acid (ILA) in complex culture media. In this study, a relationship between concentrations of PLA, ILA, and hydroxy PLA (OH-PLA) and initial concentrations of phenylalanine, tryptophan, and tyrosine, added respectively as unique sources of nitrogen in synthetic medium, was established. Phenylpyruvic acid (PPA), an intermediate compound of PLA metabolism, was able to induce not only PLA but also phenylethyl alcohol (PEA) production when used separately as initial substrate. Under pH, temperature, and salt concentrations used for cheese-making, phenylalanine was found to be the most efficient substrate for antimicrobial metabolite production. In excess of substrate, different yeast strains of Geotrichum candidum, Yarrowia lipolytica, Candida natalensis, and Candida catenulata were shown here to produce 1.6 0.5–5.0 0.2 mM of PLA from phenylalanine, 5.0 0.1–10.9 0.3 mM of ILA from tryptophan, and 1.3 0.3–7.0 0.02 of PLA and 0.1 0.0–2.22 0.09 mM of PEA from PPA. Geotrichum candidum ATCC 204307 was the highest producer. This is the first time these antimicrobial metabolites PLA, OH-PLA, ILA, and PEA are being reported as the reaction products of aromatic amino acids catabolism in G. candidum. Antilisterial metabolite; Geotrichum candidu

Behaviour of different cementitious material formulations in sewer networks

Sewer networks are subjected to degradation, including biodeterioration of materials, in the presence of biogenic sulfuric acid, leading to costly repairs. To ensure durable structures, it is essential to select the best adapted materials. Two cementitious materials based on ordinary Portland cement (OPC) or calcium aluminate cement (CAC), were subjected to biodeterioration in the headspace of an operating sewer network. After a few month OPC materials started to deteriorate whereas CAC materials were still intact. The better durability of CAC materials is due to the presence of alumina providing a combination of protective mechanisms. On-site environmental parameters were monitored and analysed in the context of the biological and chemical mechanisms involved in material degradation. These data will eventually feed into the development of a representative, reproducible and accelerated laboratory test

Definition of an appropriate cementitious material formulation for sewer networks

Sewer networks are subjected to many degradations including biodeterioration of materials in the presence of biogenic sulfuric acid, leading to costly rehabilitation. To ensure durable structures, it is necessary to select the most adapted materials. Two cementitious materials based on ordinary Portland cement (OPC) or Calcium Aluminate Cement (CAC), were submitted to biodeterioration in the headspace of an operating sewer network. After few months OPC materials start to deteriorate whereas CAC materials are still intact. The better durability of CAC materials is due to the presence of alumina providing a combination of protective mechanisms. On-site environmental parameters have been monitored and analysed in the context of the biological and chemical mechanisms involved in material degradation. These data will eventually feed the development of a representative, reproducible and accelerated laboratory test

Development of a reproducible, representative and accelerated biogenic corrosion test to reach sustainable structures in sewer networks

Cementitious materials biodeterioration in sewer networks is an important problem for sewer networks managers. This deterioration process is due to the implication of two biofilm involved in the sulfur cycle. Microorganisms of the first biofilm will reduce sulfate and organic sulfur compounds into H2S in the effluent and then, the second biofilm oxidizes it into sulfuric acid in the structure headspace. This biogenic acid usually leads to the cementitious matrix dissolution. However, cementitious materials do not equivalently face biogenic acid attack. In very aggressive conditions, those made of ordinary Portland cement are highly deteriorated while those based on calcium aluminate cement show good on-site performances. So far, only chemical testing standard procedures are available to predict service life of materials intended for sewer networks but they are not representative of the phenomenon because they do not consider microbial development. Nowadays, it is necessary to develop a new test that could be standardiable involving microorganisms. Such a test has been developed at Ifsttar and provides interesting results

Biogenic corrosion mechanism: study of parameters explaining calcium aluminate cement durability

Sewer networks should withstand several aggressions, including biodeterioration processes. This study is focusing on cementitious materials since, depending on their composition, these materials do not display the same behaviour when biogenic sulfuric acid attack occurs. In severe conditions, ordinary Portland cement materials can be deteriorated, while calcium aluminate cement (CAC) materials show good resistance to biogenic corrosion. Results show that this durability difference is due to the difference of cement mineralogy. Firstly, the H2S abiotic oxidation into elemental sulfur is less favourable on CAC. Hence it provides much less nutrients for sulfur-oxidizing microorganisms. Then, the presence of high aluminium content in CAC provides a combination of interesting properties to face biogenic acid attack. The hydrated alumina reacts with acid to create an alumina gel layer, stable up to pH 3-4. The acid attack leads to the release of aluminium ions displaying a bacteriostatic effect on neutrophilic sulfur-oxidizing microorganisms. Finally, an alumina gel precipitates on the surface. This gel has an impact on cement surface porosity which therefore reduces the acid impact and probably limiting biofilm adhesion