The present study investigates the corrosion development and induced cracks in reinforced concrete specimens submitted to an accelerated corrosion test. The accelerated chloride-induced corrosion test was performed using an impressed current mode. Three current densities (50, 100 and 200 µA/cm2 of steel) and different exposure times were considered. The objective of the experiments is to analyse two distinct types of damage: firstly, internal damage near the steel/concrete interface, which can be observed in the distribution of corrosion products, as well as damage within the concrete cover, which manifests as cracking. Secondly, external damage, which can be observed in the form of rust spots and concrete surface cracks. The aim of this analysis is to elucidate the relationship between internal damage and external damage. The study confirmed that the corrosion products are non-uniformly distributed around and along the steel reinforcing bar. It also highlighted that the accelerated corrosion test conditions, such as current density, duration, environmental conditions and the specimen geometry, have a significant influence on the distribution of the corrosion products and their thickness around the steel reinforcement and therefore on the internal and external crack patterns. The data analysis revealed a substantial dispersion and contrast in terms of the data, which precluded the establishment of a definitive correlation between internal and external deterioration.

The corrosion of carbon steel reinforcements is the main cause of deterioration in reinforced concrete structures. Stainless steel can be a solution to increase the service life of structures exposed to severe chloride environments. This paper describes the results obtained in an experimental study seeking to monitor corrosion over a long-term period (10 years) without the use of accelerated tests. Concrete samples containing admixed chloride and reinforced with 5 different steel grades were exposed to high temperature and high relative humidity in a climatic chamber for 10 years. Visual inspection, corrosion potential, linear polarisation resistance and electrochemical impedance spectroscopy measurements were carried out throughout this period. Corrosion current density was calculated to monitor the evolution of corrosion. The methodology was validated on a martensitic stainless steel (grade 1.4021) with the original finding that corrosion occurs over three time steps. None of the duplex steels (grades 1.4062, 1.4362 and 1.4462) showed corrosion after 10 years, making them a very interesting solution for structures located in severe chloride environments. Mass loss corrosion laws over time were determined. Prediction of corrosion was discussed.Please check and confirm the edit made in the article title.confirmedKindly check and confirm the organization name for affiliations 1 and 2.affiliation 1: OK affiliation 2: OK

Regulations on wastewater treatment (UWWTD-1991; WFD 2000) have evolved considerably over the past 25 years with the development of increasingly efficient bioprocesses that limit environmental risks. High-performance bio-physico-chemical wastewater treatment technologies were implemented for the plants of the main urban areas i.e. biofiltration, membrane bioreactors. Thus, over the last ten years, new types of degradation of concrete structures were observed in wastewater treatment plants, mainly in nitrification basins treating nitrogen compounds (ammonium) in effluents. The exact origins of these degradations are not yet determined. In order to understand the degradation mechanisms of concrete in nitrogen compound treatment basins, mortar specimens based on CEM V and CAC cements were exposed (i) in situ of one nitrogen treatment basin and (ii) in reactor for biological lab test. The design and implementation of the biological test were developed to reproduce were developed to reproduce nitrogen biological treatment and evaluate the degradation of mortars in a more controlled environment than the full-scale process. This laboratory test allows the evaluation of the biotic aspect of nitrification and in particular, the influence of acid production during biotic reactions and the influence of carbonates on mortar specimens. These two approaches allow highlighting the significant impact of the biomass and the modification of the environmental conditions at the biofilm/material interface.

The objective of this study is to reproduce, with large size laboratory concrete specimen, the non-uniform heating that is naturally observed in some civil engineering structures. The aim is to obtain a reliable predictive model, making it possible to evaluate the risk of developing certain pathologies such as Delayed Ettringite Formation (DEF) due to the temperatures reached and their distribution in the concrete. To this end, the dimensions and characteristics of the formwork were first determined from numerical simulations. Then, the formwork was supplemented with sensors to record the temperatures in the three spatial directions over time. The results showed that the sensors recorded a high temperature in the core of the specimens, exceeding 80 ℃, and that there were large temperature variations between the surface and the core of the concrete.

The industrial adoption of new supplementary cementitious materials requires the understanding of their effects on the hydration and on the long-term properties of concrete , in order to adapt design and construction methods. Although the evolution of properties differs from that of Portland cement systems, the constructability of glass powder (GP) blended-cement systems was found to be maintained (i.e., similar 2-day strength) and gains were observed in the long-term performances (i.e., similar strength but higher resistivity, suggesting higher durability). This paper aims to understand and describe the mechanisms responsible for these behaviours using a multi-technique investigation approach (calorimetry, XRD-Rietveld-PONKCS, thermodynamic modelling , quantitative chemical analyses, and more). The results disclose the chemo-physical effects of GP on early age hydration kinetics , the impact of cement dilution on phase assemblage, and the long-term pozzolanic reaction of GP leading to C-S-H with a lower calcium content, a higher alkali uptake and a refined porosity.

In a context of ageing reinforced concrete structures, electrochemical chloride extraction (ECE) is an interesting treatment for structures damaged by chloride-induced corrosion. This paper summarises the state of the art by presenting the concept of ECE, assessing available measurement techniques and discussing influencing factors. The determination of ECE efficacy requires the consideration of different results, and particularly those pertaining to chloride extraction, corrosion mitigation and evolution of pH. This literature review also highlights the potential side effects and risks to the concrete structure. Further work is needed to ascertain the long-term performance of ECE.

In wastewater treatment plants, nitrification is a biological treatment stage, which leads to the production of nitrate ions from nitrate ions using nitrifying bacteria. The structures in which the nitrification takes place are built with cementitious materials, which have degradations more and more apparent in recent years. In the literature, only one study from a Swiss team is available about the deterioration of concrete in nitrification structures. It is reported in this study that the observed degradations have a biological origin and resulted from the acidity generated by the nitrifying biological activity at the interface concrete/biofilm. However, other parameters that are not discussed in this study may be responsible for the degradation of concrete. A detailed study of the degradation mechanisms is necessary in order to qualify and quantify the degradation in nitrification structures. Indeed, the degradations may have a chemical origin, a mechanical origin or a biological origin. This bibliographical article aims to describe and to analyze the different chemical, biological and mechanical parameters which may have an influence on the degradation of concrete in nitrification structures.

Le changement climatique et les modifications de pratiques induisent une augmentation de la teneur en hydrogène sulfuré dans les réseaux d’assainissement. Outre l’aspect sanitaire, l’H2S peut être responsable de la dégradation des canalisations et/ou infrastructures en béton, en particulier lorsqu’il est oxydé par des micro-organismes sulfo-oxydants avec formation d’acide sulfurique. Cet acide réagit avec les composés alcalins du béton et notamment avec l’hydroxyde de calcium pour former du gypse, composé expansif. Dans ces conditions et en fonction de la teneur en H2S, des dégradations importantes sont observées qui peuvent quelquefois conduire à l’effondrement du béton dans la partie aérienne. Des recommandations sur le choix des ciments sont proposées pour ces environnements, mais ne donnent pas entière satisfaction compte tenu du manque de données sur le comportement des matériaux cimentaires en fonction de la teneur en H2S. Dans cette étude, trois mortiers formulés avec des ciments différents ont été exposés sur six sites différents en France afin d’essayer de mieux définir les classes d’exposition définies dans le fascicule FD P18-011 relatif aux environnements contenant de l’H2S. L’utilisation de teneur moyenne en H2S ne semble pas la donnée la plus judicieuse pour classer les environnements, l’utilisation du 3e quartile apparaît comme un paramètre plus approprié. Il est ainsi possible de former trois classes : la classe 1, le 3e quartile est inférieur à 8 ppm ; la classe 2, le 3e quartile est compris entre 8 et 15 ppm ; et la classe 3, le 3e quartile est supérieur à 15 ppm.

Polymer-modified mortars are cementitious materials that integrate polymers from 5 to 20 wt.%. Those materials are widely used for protecting and/or repairing concrete surfaces among which building facades, civil engineering structures, or sewage networks. In this context, polymer-modified mortars are applied into thin layers of about 1–3 cm. However, previous studies performed regarding such materials were carried out on massive pieces and did not consider the interactions between polymer-modified mortars and microorganisms. Nevertheless, such interactions can lead to undesired aesthetical or structural modifications of those materials. As a result, the main objective of this paper is to evaluate the resistance to biocolonisation of polymer-modified mortars applied into thin layers in environmental conditions that are representative of the on-site applications. Two formulations of polymer-modified mortars and a polymer-free mortar are characterised in the hardened state. Then, the resistance of those mortars to biocolonisation is tested by means of two laboratory accelerated tests. The first experiment is performed in order to recreate biofouling at the surface of the specimens, while the second one exposes the materials to biodeterioration. The results and analyses show that in the presence of polymer, both porosity and capillary absorption of mortars are reduced, but this does not allow preventing or slowing down biocolonisation. In addition, this study suggests that the nature of the polymer has an influence on bioreceptivity of polymer-modified mortars. Finally, our results suggest that in the presence of polymer, the global material may have an improved inner cohesion.

The influence of sewage sludge ash (SSA) on the hydration of Portland cement (OPC) was investigated in this study. Blending OPC with SSA was found to influence the kinetic of hydration, notably the alite dissolution. This retardation effect has been attributed to the presence of the orthophosphate ions (PO43−). However, SSA releases only a small fraction of PO43− into solution, which is deemed insufficient to precipitate calcium phosphates compounds on noticeable levels at least. On the other hand, an enhancement of the engineering-scale properties (i.e. mechanical and durability) and portlandite consumption are observed when SSA is used. This is explained by the formation of AFm phases, which leads to changes in the total volume of the solid and thus the properties of the systems. These experimental results were confirmed by thermodynamic modelling, showing that the additional alumina released by SSA results in the formation of higher amount of AFt and AFm phases.

The objective of this study was to evaluate the use of rhamnolipids (RLs) extracted from Pseudomonas aeruginosa as a possible eco-friendly inhibitor for the corrosion protection of rebars in concrete. Two application methods were tested: application of RLs as a coating on the steel (conditioning method) and addition of the RLs directly to the aggressive environment (addition method). Both methods were evaluated for their ability to protect steel in simulated concrete pore solution containing 0.5M NaCl. The results highlight a delay in the initiation of local corrosion followed by a rapid propagation rate of corrosion for conditioning method. This evolution is in relation with the heterogeneity of the formed RLs layers. The addition method provides a different film formation and better protection against corrosion. Using a 1gL concentration, the inhibition effect was observed at least for 24h of immersion.

X-ray diffraction (XRD) is a prominent technique to characterise cement-based materials. The combination of the Rietveld refinement with the Partial Or No Known Crystal Structure (PONKCS) approach now enables the quantification of both crystalline phases and amorphous contribution of SCMs. This paper describes the application of Rietveld-PONKCS to determine the amount of reacted glass powder (GP) in blended cement pastes. The accuracy and precision of the method were compared to the results of independent methods such as selective acid dissolution, thermogravimetric analysis (TGA) combined to energy-dispersive spectroscopy (EDS) or inductively coupled plasma (ICP) applied to GP-lime mixtures. For blended cement, the consistency of the method was internally checked using the standard addition method. Overall, an average precision of 1.6 wt% and accuracy better than 1.5 wt% were found for Rietveld-PONKCS applied to GP containing systems.

En assainissement, la nitrification est une étape de traitement biologique qui permet, par l’intermédiaire de bactéries nitrifiantes, de transformer les ions ammonium en ions nitrate. Les ouvrages dans lesquels se déroule la nitrification sont construits avec des matériaux cimentaires qui subissent des dégradations de plus en plus visibles ces dernières années. Dans la littérature, il n’existe qu’une seule étude réalisée par une équipe suisse qui s’est intéressée à la détérioration du béton dans les ouvrages de nitrification. Il est reporté dans ces travaux que les dégradations observées sur les ouvrages ont une origine biologique et résultent de l’acidité générée par l’activité biologique nitrifiante à l’interface paroi en béton/biofilm. Néanmoins, d’autres paramètres qui ne sont pas pris en compte peuvent être responsables de la dégradation du béton, ce qui signifie qu’une étude plus détaillée des mécanismes de dégradation est nécessaire pour bien qualifier et quantifier les dégradations dans les ouvrages de traitement biologique. En effet, les dégradations peuvent avoir une origine chimique, une origine mécanique ou une origine biologique. Cet article bibliographique a ainsi pour objectif de décrire et d’analyser les différents paramètres chimiques, biologiques et mécaniques susceptibles d’avoir une influence sur la dégradation du béton dans les ouvrages de nitrification.

Civil engineering structures and historical buildings can suffer from corrosion of the embedded reinforcing steel once the concrete cover is totally carbonated and/or when chloride ions reach the steel/concrete interface. On field, these two types of contamination can be encountered separately or combined requiring implementation of proper repair methods. In this study, in a first step, corrosion of both chlorinated and carbonated reinforced concrete specimens were followed during casting and accelerated contaminations. In a second step, electrochemical chloride extraction was performed as a repair treatment (cathodic polarization, 1 A/m² of steel surface during 8 weeks). The efficiency of the treatment and its impact on the cement matrix and at the concrete-steel interface were studied during the treatment, after rebar depolarization and in the long term (several months) in order to evaluate its durability. In order to achieve these aims, three analysis means were used: electrochemical characterization, scanning electron microscopy and Raman microspectroscopy. In this paper, results obtained on specimens cast with CEM III cement (often encountered on reinforced concrete historical monuments) with chlorides addition into the mix water and further accelerated carbonation are presented. Study of rebar’s electrochemical characteristics during the artificial aging highlighted an increase of corrosion rate from negligible value of 0.1 µA/cm² after fabrication to about 10 µA/cm² after carbonation. SEM observations confirmed this phenomenon with the identification of a corrosion layer on most of the concrete/steel interface after carbonation. The ECE efficiency was demonstrated by a chloride extraction of about 97% at the rebar level which yields a decrease of chloride ions concentration below the theoretical threshold value of 0.4 % by mass of cement after two weeks. Simultaneously a realkalisation ring was observed on concrete around the reinforcement bar which reached almost 1 cm after 56 days. After depolarization, results showed that a duration of 28 days of ECE treatment allowed the stabilization of the corrosion state of the rebar. Raman microspectroscopy allowed to study in situ, thanks to specific cells, the corrosion products’ reduction during the treatment.

The use of glass powder (GP) as an alternative SCM offers a viable opportunity to partially substitute OPC, and therefore provides economic and environmental benefits. Moreover, the predominant siliceous amorphous phase provides the required component for its use as pozzolanic material. In this work, the mechanism and the products of the finely ground GP reaction with lime are investigated. The released silica, from glass dissolution, reacts with calcium hydroxide (CH) to form C-(N)-S-H with different compositions depending on the system. In the studied CH-GP binder systems, the fineness of GP ensures a higher surface for silica to react, leaving time for the pozzolanic reaction to take place. However, the glass continues to react even after the consumption of CH, which may lead to the apparition of alkali-silica gels around the particles in the long term.